Self-recoverable covering material and method for fabricating the same

BACKGROUND OF THE INVENTION
The present invention relates to a process and composition of matter capable of recovering cracks generated in mechanical structural components.
When metals, carbon/carbon-fiber composites (hereinafter, referred to as "C/C composite") and non-oxide ceramics are used in high temperature oxidizing atmospheres, the surfaces thereof are oxidized. To prevent the oxidization, the surfaces of the above materials are covered with isolating layers having protective materials therein (hereafter sometimes referred to as "PMs", for example, zirconium dioxide). For example, a method of covering zirconium dioxide as an isolating layer on the surface of a metal member is disclosed in Unexamined Japanese Patent Publication Nos. SHO 55-28351 and SHO 58-87273. A method of covering a carbon member with zirconium dioxide as an isolating material is disclosed in Unexamined Japanese Patent Publication No. SHO 58-125679; and a method of covering a silicon nitride member with zirconium dioxide as an isolating layer is disclosed in Examined Japanese Patent Publication No. HEI 5-8152. Further, it is known to cover a cutting tool with a boride and then with alumina for increasing the adhesiveness of the covering.
In non-oxide ceramics, it is also known that they are heated in the atmospheric air at high temperatures to recover voids and cracks generated on the surface.
The above-described references, however, do not examine the reliability under the actual service environment. For example, if a base material is covered with an oxide, such as zirconium dioxide, at the time when the covering layer is cracked, due to its inherently brittle nature, the base material, having a poor resistance to an environmental reactive material (here, oxygen), is exposed and is rapidly oxidized. The base material is oxidized by the generation of cracks, resulting in reduced mechanical strength.
Accordingly, there is a need for an isolating layer which when used will resist reaction of a base material with an environmentally reactive material (hereafter sometimes referred to as "ERM") when the isolating layer is cracked. An object of the present invention, therefore, is to provide a self-recoverable isolating layer having a reactive material (hereafter sometimes referred to as an "RM") which, when exposed to an environmental reactive material ("ERM") reacts with the ERM to recover cracks generated on an outermost surface of the isolating layer.
SUMMARY OF THE INVENTION
To achieve the above object, according to an embodiment of the present invention, the surface of a member formed of a base material (for example: ceramics, metals and/or C/C composites) is covered with an isolating layer having a reactive material therein, wherein the reactive material reacts upon exposure to the environmental reactive material to form a protective material.
According to a more specific embodiment, the isolating layer comprises a reactive material and a protective material, distributed such that there is more protective material near the environmental reactive material and more reactive material near the base material. According to still a more specific embodiment, the isolating layer comprises two distinct layers, wherein the layer closest to the environmental reactive material comprises a protective material and the layer closest to the base material comprises a reactive material.
In a more specific embodiment of the present invention, the surface of a member formed of at least one kind of ceramics, metals and C/C composites, is covered with an outermost surface oxide protective layer having a stability against the environment in the atmospheric air at 1500.degree. C., and a self-recoverable layer of reactive material formed between the outermost surface oxide covering layer and the surface of the member. According to one such embodiment, the self-recoverable layer has an oxidizing rate greater than that of the outermost surface covering layer for recovering cracks generated on the outermost surface covering layer, and a compound produced by the self-recoverable layer has the same phase as in the outermost surface covering layer. To achieve the optimum self-recovering function at high temperatures in one such embodiment, the outermost surface oxide covering layer comprises a stable oxide having a vapor pressure of 1.times.10.sup.-4 N/m.sup.2 or less in the atmospheric air at 1500.degree. C., and the oxidized product material from the self-recoverable layer contains an oxide having the same composition as that of the outermost surface oxide covering layer.

DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and for further advantages thereof, reference is made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a top view showing the concept of a self-recoverable covering material according to an example of the present invention;
FIG. 2 is a life diagnostic circuit diagram showing another example of the present invention;
FIG. 3 is a three-dimensional view showing the construction of a self-recoverable layer by a laminating method according to a further example of the present invention;
FIG. 4 is a view showing the appearance of a ceramic gas turbine moving blade to which the present invention is applied;
FIG. 5 is a view showing the appearance of a ceramic gas turbine stator blade to which the present invention is applied;
FIG. 6 is a schematic view of a continuous hot dip metal plating apparatus to which the present invention is applied;
FIG. 7 is a view showing the appearance of a tile for combustor to which the present invention is applied, and also showing the concept of a life diagnostic function;
FIG. 8 are electron micrographs showing the crystal structures of SiC before and after an oxidizing test;
FIG. 9 are electron micrographs showing the crystal structures of Si.sub.3 N.sub.4 before and after an oxidizing test; and
FIG. 10 is a diagram showing the change of weight in the thermal analysis made for a self-recoverable covering material according to an example of the present invention.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION
Prior to the description of specific embodiments, the feature of a self-recoverable covering material of the present invention will be described below.
One embodiment of a self-recoverable layer according to the present invention includes a boron compound or silicon compound. The compound reacts with an oxidizing atmosphere, and produces a reaction product material capable of recovering cracks. In the present invention, to achieve the self-recovering function, the oxidized product material generated from the self-recoverable layer contains an oxide having the same composition as that of the outermost surface oxide covering layer. Moreover, in order that the self-recoverable layer can fully achieve the self-recovering function, the outermost surface covering layer resisting the environment is made of an oxide.
For example, according to one embodiment of the invention, the surface of a gas turbine moving blade made of silicon nitride is covered with a self-recoverable layer made of ZrB.sub.2 and an outermost surface made of ZrO.sub.2. In such a structure, cracks are given on the surface of the ZrO.sub.2 layer. The structure is then kept in a high temperature oxidizing atmosphere at 1500.degree. C. In this example, the ZrB.sub.2 layer is oxidized to produce compounds of ZrO.sub.2, B.sub.2 O.sub.3 and ZrBO, and the cracks on the outermost ZrO.sub.2 layer are recovered by the compounds containing the ZrO.sub.2 component. The covering layer thus obtained has a reliability higher than that in an conventional structure covered with only the ZrO.sub.2 layer. Here, the oxidizing rate of ZrB.sub.2 is more than that of ZrO.sub.2. ZrO.sub.2 is stable at high temperatures, which has a vapor pressure of 5.6.times.10.sup.-8 N/m.sup.2 in the atmospheric air at 1500.degree. C. FIG. 1 is a view showing the concept of the self-recovering function.
According to various embodiments of the present invention, the surface of a member formed of at least one kind of ceramics, metals and C/C composites is covered with an oxide, and a layer containing at least a boron compound or silicon compound between the oxide and the member. In this member, thermal expansion coefficients of the member, intermediate layer, and oxide layer are gradually changed. This is because the thermal impact generates a lot of cracks, due to the difference in the thermal expansion coefficient, not only on the outermost surface oxide but also on the self-recoverable layer. In particular, when the difference in the thermal expansion coefficient is large, not only vertical cracks but also transverse cracks are generated, which causes the peeling of the layers.
To achieve the self-recovering function in some specific embodiments of the present invention, the self-recoverable layer comprises at least one kind of borides of Zr, Hf, Ta, Al and Y or at least one kind of silicates of Zr, Hf, Ta, Al and Y, in an amount of 30 vol % or more. When the content of the borides or silicates is less than 30 vol %, the dispersibility is poor as a whole, and, therefore, the recovering function cannot be fully achieved.
According to some embodiments, the self-recoverable layer includes one or more layers. To enhance the reliability, two or three layers are preferably provided.
According to yet a further embodiment of the invention, reaction product material obtained by the self-recovering function, mainly comprises one kind or more crystalline materials selected from a group consisting of: ZrO.sub.2, Al.sub.2 O.sub.3, HfO.sub.2, zircon (ZrO.sub.2 /SiO.sub.2), mullite (3Al.sub.2 O.sub.3 /2SiO.sub.2), ZrO.sub.2 and B.sub.2 O.sub.3, Al.sub.2 O.sub.3 and B.sub.2 O.sub.3, zircon (ZrO.sub.2 /SiO.sub.2) and B.sub.2 O.sub.3, mullite (3Al.sub.2 O.sub.3 /2SiO.sub.2) and B.sub.2 O.sub.3, HfO.sub.2 and B.sub.2 O.sub.3, Y.sub.2 O.sub.3 and B.sub.2 O.sub.3, Ta.sub.2 O.sub.5 and B.sub.2 O.sub.3, HfO.sub.2 and SiO.sub.2, Y.sub.2 O.sub.3 and SiO.sub.2, and Ta.sub.2 O.sub.5 and SiO.sub.2. Alternately, the reaction product material comprises one kind or more of crystalline materials selected from a group consisting of Al.sub.2 O.sub.3 --BaO, Al.sub.2 O.sub.3 --BeO, Al.sub.2 O.sub.3 --MgO, Al.sub.2 O.sub.3 --MnO, Al.sub.2 O.sub.3 --SiO.sub.2, Al.sub.2 O.sub.3 --TiO.sub.2, Al.sub.2 O.sub.3 --ZnO, Al.sub.2 O.sub.3 --ZrO.sub.2, ZrO.sub.2 --TiO.sub.2, ZrO.sub.2 --SiO.sub.2, ZrO.sub.2 --Nb.sub.2 O.sub.5, K.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2, MgO--Al.sub.2 O.sub.3 --SiO.sub.2, Al.sub.2 O.sub.3 --CeO.sub.2, CaO--Al.sub.2 O.sub.3 --SiO.sub.2, BaO--Al.sub.2 O.sub.3 --SiO.sub.2, FeO--Al.sub.2 O.sub.3 --SiO.sub.2, CaO--MgO--SiO.sub.2, CaO--ZrO.sub.2 --SiO.sub.2, MgO--CaO, MgO--SiO.sub.2, Hexacelsian, MgO--TiO.sub.2, MgO--ZrO.sub.2, and SiO.sub.2 --TiO.sub.2. The above oxides such as ZrO.sub.2, Al.sub.2 O.sub.3, MgO, Y.sub.2 O.sub.3 are stable at high temperatures, which have vapor pressures of 1.times.10.sup.-4 N/m.sup.2 or less in the atmospheric air at 1500.degree. C.
When the self-recoverable layer is formed of vitreous oxides of B, Ba, Mg, Ti, Li, Na, Nb, K, and V, the temporary recovering is possible; however, the glass having a high vapor pressure disappears by vaporization, and does not act as the recoverable layer. The product material generated from the self-recovering layer must be stable in the service environment.
The present invention is not dependent on the structure to be covered. Therefore, the structure to be covered is not particularly limited, and, according to example embodiments comprise ceramics, metals and/or C/C composites. Examples of ceramic structure to be covered includes: SiC, mullite, Si.sub.3 N.sub.4, sialon, AlN, and Si.sub.2 N.sub.2 O, and composite materials, for example: SiC, ZrO.sub.2, mullite, Si.sub.3 N.sub.4, AlN, Al.sub.2 O.sub.3, B.sub.4 C, BN, Si.sub.2 N.sub.2 O, or Y.sub.2 O.sub.3. According to embodiments of the invention, covered composites have a nanocomposite structure where different particles are dispersed within matrix particles and/or at the grain boundaries. According to other embodiments, composites to be covered include, for example, a reaction-sintered composite material containing 5 to 60 vol % of inorganic compound composed of at least one kind of oxide, carbide, nitride and carbide-nitride and 95 to 40 vol % of metal nitride, which has a structure where the inorganic compound particles are bonded with each other by means of the metal nitride. According to still further embodiments, composites to be covered include metals and alloys such as Fe alloy, Al alloy, Ti alloy, Ni alloy, intermetallic compound, one-way solidified metal monocrystalline metal, cast iron, carbon steel, and heat-resisting steel.
As yet a further example of an embodiment of the present invention, there is provided a life diagnostic circuit on a mechanical structural component having a self-recoverable covering layer. In this case, the life diagnostic circuit is not provided throughout the whole component, but is provided only near the portion where the maximum stress is generated or only at the plane where oxidization is generated. However, the life diagnostic circuit must be provided near the surface of the self-recoverable layer (within 5 mm from the surface). In the structural member, cracks are first generated on the surface and generates the breakage; accordingly, it is required to sensitively detect the generation of the cracks on the surface of the self-recoverable layer. A bundle of fibers (usually: 100 to 1000) are provided as a resistance measuring circuit for life diagnosis. As cracks propagated from the surface cut the fibers, the resistivity is increased. When the resistivity exceeds the set-up threshold value, it is judged that maintenance is required. The equipment is stopped and the parts are exchanged. In the case of a bundle of long fibers, a bundle of combined short fibers or a bundle of fibers of combined particles, cracks cut the fibers in the bundle little by little, so that the resistivity is also increased little by little.
A conductive circuit may be provided near the covering layer of a mechanical structural component having a self-recoverable covering layer. The life of the self-recovering function can be predicted by measuring the change in the resistivity of the conductive circuit (FIG. 2). The conductive circuit for measuring the life is formed of fibers and particles having a low resistivity such as C, SiC, TiN, TiC, ZrN and Cr.sub.2 N. It may be formed of two kinds of fibers or particles having different elasticities for enhancing the efficiency of the life diagnosis. In particular, it is important that the conductive circuit for measuring a life serves as a reinforcing material for the mechanical structural component. The resistivity of the conductive circuit for measuring a life is changed due to the phenomena generated on a bundle of fibers constituting the conductive circuit, such as drawing, cutting, interface (contact) change, deformation, chemical corrosion, and temperature change. The conductive circuit measures the above change in the resistivity, and compares it with a threshold value, thus performing the prediction of a life, diagnosis of the life and the diagnosis of maintenance. For example, when cracks are generated on the surface and the self-recoverable layer is oxidized for achieving the recovering function, the further the oxidization proceeds, the conductive circuit for measuring the life is oxidized, thus increasing the resistance. The value thus obtained is read out, and is compared with a threshold value by a computer provided on the outside of the system. When the value exceeds the threshold value, the stopping signal is automatically outputted. Thus, it becomes possible to stop the equipment before breakage of the mechanical structural component, and to exchange the parts.
The change in the resistance value is supplied to a system, and the system is automatically stopped when the resistance value exceeds a threshold value, thereby performing the maintenance and checking.
Various embodiments of the covering method of the present invention include spraying, chemical deposition, physical deposition, coating, dipping, laminating, and the like. According to some embodiments, the actual covering method is selected based on adhesiveness and does not exert an effect on the self-recovering function. For metals and C/C composites, plasma spraying is desirable. For ceramics, plasma spraying, laminating and chemical deposition are desirable.
According to still a further embodiment of the present invention, a barrier for preventing oxidization is interposed between the surface of the structure made of a ceramic or C/C composite and the self-recoverable layer.
The present invention will be more clearly understood with reference to the following examples:
EXAMPLES 1 TO 95
The surface of each of structures made of ceramics and C/C composites shown in Table 1 was covered with each self-recoverable layer shown in Table 1 to a thickness of 200 .mu.m, and each outermost surface layer such as ZrO.sub.2 shown in Table 1 to a thickness of 200 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost surface layer thus obtained were dense with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the outermost surface of the structure. The structure was then kept for 100 hr in the atmospheric air at 1500.degree. C. As a result, the crack portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500 degrees C. Each component of the recovered portion was shown in Tables 1 to 3. The concept of the recovering function is shown in FIG. 1.
As a comparative example, a SiC sintered body was covered with ZrO.sub.2 to a thickness of 200 .mu.m without any self-recoverable layer. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the outermost surface of the SiC sintered body. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C.
FIG. 8 shows electron micrographs of the above SiC sintered body before and after the oxidizing test. In these micrographs, multiple large voids were generated because SiO.sub.2 was produced on the cracked portion of the surface of the SiC sintered body and then evaporated, as a result of which the SiC sintered body was eroded. As another comparative example, a Si.sub.3 N.sub.4 sintered body was covered with ZrO.sub.2 to a thickness of 200 .mu.m without any self-recoverable layer. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the outermost surface of the Si.sub.3 N.sub.4 sintered body. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C.
FIG. 9 shows electron micrographs of the above Si.sub.3 N.sub.4 sintered body before and after the oxidizing test. In these micrographs, a SiO.sub.2 oxide film was produced on the cracked portion of the surface of the Si.sub.3 N.sub.4 sintered body and simultaneously an oxide of Yb as a sintering assist agent was melted and precipitated on the surface layer, as a result of which the Si.sub.3 N.sub.4 sintered body was eroded. Consequently, it was revealed that the surface of SiC or Si.sub.3 N.sub.4 sintered body with no self-recoverable layer was eroded by oxidization. The erosion causes the reduction in the reliability.
In these examples, it is important that the oxidizing rate of the self-recoverable layer is more than that of the outermost surface layer. The effect of the self-recoverable layers of the present invention is not limited to the ceramics and C/C composites used in these examples, but may be applied to all of ceramics, C/C composites and metals.
The outermost surface layer may be made of a compound resisting an outer environment, preferably, a compound such as ZrO.sub.2, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, HfO.sub.2 or Ta.sub.2 O.sub.5 for a high temperature environment. In combination with the above compound, a self-recoverable layer is suitably selected from a boron of Zr, Al, Y, Hf or Ta.
B.sub.4 C, B.sub.4 C+B, or the like used for a self-recoverable layer has no self-recovering function. The reason for this is that CO gas is generated when B.sub.2 O.sub.3 glass is produced by the reaction between B.sub.4 C, or B.sub.4 C+B, and oxygen in the atmospheric air; the reaction gas generates voids or cracks at the recovered portion; and the B.sub.2 O.sub.3 glass is vaporized because of its large vapor pressure.
TABLE 1______________________________________ Self- Recoverable OutermostNo. Structure Layer Surface Layer Recovered Product______________________________________1 Si.sub.3 N.sub.4 ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.32 Si.sub.3 N.sub.4 TiB.sub.2 TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.33 Si.sub.3 N.sub.4 ZrB.sub.2 + HfB.sub.2 ZrO.sub.2 ZrO.sub.2, HfO.sub.24 Si.sub.3 N.sub.4 CaB.sub.2 CaO CaO, B.sub.2 O.sub.35 Si.sub.3 N.sub.4 WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.36 Si.sub.3 N.sub.4 LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.37 Si.sub.3 N.sub.4 HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.38 Si.sub.3 N.sub.4 TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.39 Si.sub.3 N.sub.4 NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.310 Si.sub.3 N.sub.4 FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.311 Si.sub.3 N.sub.4 AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.312 Si.sub.3 N.sub.4 ZrB.sub.2 + SiO.sub.2 ZrO.sub.2 ZrO.sub.2, ZrSiO.sub.413 Si.sub.3 N.sub.4 HfB.sub.2 + SiO.sub.2 HfO.sub.2 HfO.sub.2, HfSiO.sub.414 Si.sub.3 N.sub.4 ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.215 Si.sub.3 N.sub.4 ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.216 SiC ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.317 SiC TiB.sub.2 TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.318 SiC CaB.sub.2 CaO CaO, B.sub.2 O.sub.319 SiC WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.320 SiC LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.321 SiC HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.322 SiC TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.323 SiC NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.324 SiC FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.325 SiC AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.326 SiC ZrB.sub.2 + SiO.sub.2 ZrO.sub.2 ZrO.sub.2, ZrSiO.sub.427 SiC HfB.sub.2 + SiO.sub.2 HfO.sub.2 HfO.sub.2, HfSiO.sub.428 SiC ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.229 SiC ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3,ZrO.su b.230 AlN ZrB.sub.2 ZrO.sub.2 ZrO.sub.2,B.sub.2 O.sub.331 AlN TiB.sub.2 TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.332 AlN CaB.sub.2 CaO CaO, B.sub.2 O.sub.333 AlN WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.334 AlN LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.335 AlN HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.336 AlN TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.337 AlN NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3______________________________________
TABLE 2______________________________________ Self- Recoverable OutermostNo. Structure Layer Surface Layer Recovered Product______________________________________38 AlN FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.339 AlN AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.340 AlN ZrB.sub.2 + SiO.sub.2 ZrO.sub.2 ZrO.sub.2, ZrSiO.sub.441 AlN HfB.sub.2 + SiO.sub.2 HfO.sub.2 HfO.sub.2, HfSiO.sub.442 AlN ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.243 AlN ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.244 Sialon ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.345 Sialon TiB.sub.2 TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.346 Sialon CaB.sub.2 CaO CaO, B.sub.2 O.sub.347 Sialon WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.348 Sialon LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.349 Sialon HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.350 Sialon TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.351 Sialon NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.352 Sialon FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.353 Sialon AlB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.354 Sialon ZrB.sub.2 + SiO.sub.2 ZrO.sub.2 ZrO.sub.2, ZrSiO.sub.455 Sialon HfB.sub.2 + SiO.sub.2 HfO.sub.2 HfO.sub.2, HfSiO.sub.456 Sialon ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.257 Sialon ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.258 Mullite ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.359 Mullite TiB.sub.2 ZrO.sub.2, TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.360 Mullite CaB.sub.2 CaO CaO, B.sub.2 O.sub.361 Mullite WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.362 Mullite LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.363 Mullite HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.364 Mullite TaB.sub.2 Ta.sub.2 O.sub.5 TaO.sub.5, B.sub.2 O.sub.365 Mullite NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.366 Mullite FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.367 Mullite AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.368 Mullite ZrB.sub.2 + SiO.sub.2 ZrO.sub.2 ZrO.sub.2, ZrSiO.sub.469 Mullite HfB.sub.2 + SiO.sub.2 HfO.sub.2 HfO.sub.2, HfSiO.sub.470 Mullite ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.271 Mullite ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.272 Sialon + SiC ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.373 Sialon + TiN TiB.sub.2 ZrO.sub.2, TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.3______________________________________
TABLE 3______________________________________ Self- Outermost Recoverable SurfaceNo. Structure Layer Layer Recovered Product______________________________________74 Sialon + ZrO.sub.2 CaB.sub.2 CaO CaO, B.sub.2 O.sub.375 Si.sub.3 N.sub.4 + SiC WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.376 Si.sub.3 N.sub.4 + AlN LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.377 Si.sub.3 N.sub.4 + ZrO.sub.2 HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.378 Si.sub.2 N.sub.2 O TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.379 Si.sub.3 N.sub.4 + TiCN NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.380 Si.sub.3 N.sub.4 + TiN FeB.sub.2 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.381 Si.sub.3 N.sub.4 + Mo AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.382 Sialon + Mo ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.283 TiN ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.284 BN AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.385 C/C composite ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.386 C/C composite TiB.sub.2 TiO.sub.2 TiO.sub.2, B.sub.2 O.sub.387 C/C composite CaB.sub.2 CaO CaO, B.sub.2 O.sub.388 C/C composite WB WO.sub.2 WO.sub.2, B.sub.2 O.sub.389 C/C composite LaB.sub.2 La.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.390 C/C composite HfB.sub.2 HfO.sub.2 HfO.sub.2, B.sub.2 O.sub.391 C/C composite TaB.sub.2 Ta.sub.2 O.sub.5 Ta.sub.2 O.sub.5, B.sub.2 O.sub.392 C/C composite NbB.sub.2 Nb.sub.2 O.sub.5 Nb.sub.2 O.sub.5, B.sub.2 O.sub.393 C/C composite ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.394 C/C composite ZrB.sub.2 + TiB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.295 C/C composite ZrB.sub.2 + FeB.sub.2 ZrO.sub.2 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.2______________________________________
EXAMPLES 96-102
Tests were made to examine the suitability of self-recoverable layers. The surface of a sample (10.times.10.times.5 mm) made of each structure shown in Table 4 was covered with each self-recoverable layer shown in Table 4 to a thickness of 200 .mu.m, and each outermost surface layer such as ZrO.sub.2 shown in Table 4 to a thickness of 200 .mu.m by a powder type plasma spraying. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the surface of the sample. The sample was then kept for 100 hr. in the atmospheric air at 1500.degree. C., which gave the result shown in Table 4. It was revealed that single B.sub.4 C, single B and (B.sub.4 C+SiO.sub.2) are evaporated and they had no recovering function for cracks.
Next, the change of a self-recoverable layer by the high temperature oxidization was measured by a thermobalance, which gave the result shown in FIG. 10. From this figure, it was confirmed that single B.sub.4 C, single B were perfectly evaporated by oxidization and (B.sub.4 C+SiO.sub.2) was reduced in weight by 50 wt % by oxidization.
TABLE 4______________________________________ Self- Outermost Recoverable SurfaceNo. Structure Layer Layer Recovered Product______________________________________96 Si.sub.3 N.sub.4 B.sub.4 C ZrO.sub.2 Absence of recovering function Si.sub.3 N.sub.4, eroded97 SiC BN ZrO.sub.2 Absence of recovering function SiC, eroded98 SiC B ZrO.sub.2 Absence of recovering function SiC, eroded99 C/C B.sub.4 C + SiO.sub.2 SiC Absence of recovering function C/C, eroded100 C/C BN + SiO.sub.2 SiC Absence of recovering function C/C, eroded101 C/C B + SiO.sub.2 SiC Absence of recovering function C/C, eroded102 C/C ZrB.sub.2 ZrO.sub.2 Presence of recovering function C/C, recovered by ZrO.sub.2 and the like______________________________________
EXAMPLES 103-132
The surface of each of the structures made of ceramics and C/C composites shown in Table 5 was covered with each self-recoverable layer shown in Table 5 to a thickness of 200 .mu.m, and an outermost surface layer made of each oxide shown in Table 5 to a thickness of 150 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost layer thus obtained were dense with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 150 .mu.m was given on the outermost surface of the structure. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air. Each component of the recovered portion was shown in Table 5.
TABLE 5______________________________________ Self- Recoverable OutermostNo. Structure Layer Surface Layer Recovered Product______________________________________103 Si.sub.3 N.sub.4 ZrB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3104 Si.sub.3 N.sub.4 TiB.sub.2 TiO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, B.sub.2 O.sub.3105 SiC CaB.sub.2 CaO, Al.sub.2 O.sub.3 CaO, B.sub.2 O.sub.3106 Mullite WB WO.sub.2, Al.sub.2 O.sub.3 WO.sub.2, B.sub.2 O.sub.3107 Sialon LaB.sub.2 La.sub.2 O.sub.3, Al.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.3108 C/C HfB.sub.2 HfO.sub.2, Al.sub.2 O.sub.3 HfO.sub.2, B.sub.2 O.sub.3 composite109 Si.sub.3 N.sub.4 + SiC TaB.sub.2 Ta.sub.2 O.sub.5, Al.sub.2 O.sub.3 Ta.sub.2 O.sub.5, B.sub.2 O.sub.3110 Si.sub.3 N.sub.4 NbB.sub.2 Nb.sub.2 O.sub.5, Al.sub.2 O.sub.3 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3111 Si.sub.3 N.sub.4 FeB.sub.2 Fe.sub.2 O.sub.3, Al.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3112 Si.sub.3 N.sub.4 AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3113 Si.sub.3 N.sub.4 ZrB.sub.2 + ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, HfO.sub.2, Al.sub.2 O.sub.3 HfB.sub.2 + AlB.sub.2114 Si.sub.3 N.sub.4 + ZrB.sub.2 + TlB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.3 ZrO.sub.2115 Si.sub.3 N.sub.4 + AlN ZrB.sub.2 + FeB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.2116 SiC ZrB.sub.2 Zircon ZrO.sub.2, B.sub.2 O.sub.3117 SiC TlB.sub.2 TiO.sub.2, Cr.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3118 Si.sub.3 N.sub.4 + SiC CaB.sub.2 CaO, Cr.sub.2 O.sub.3 CaO, B.sub.2 O.sub.3119 AlN WB WO.sub.2, TiO.sub.2 WO.sub.2, B.sub.2 O.sub.3120 Mullite LaB.sub.2 La.sub.2 O.sub.3, SiO.sub.2 La.sub.2 O.sub.3, B.sub.2 O.sub.3121 Sialon YB.sub.2 Y.sub.2 O.sub.3 Y.sub.2 O.sub.3, B.sub.2 O.sub.3122 C/C YB.sub.2 ZrO.sub.2, Y.sub.2 O.sub.3 Y.sub.2 O.sub.3, B.sub.2 O.sub.3 composite123 SiC NbB.sub.2 Y.sub.2 O.sub.3 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3124 Si.sub.2 N.sub.2 O ZrB.sub.2 Zircon ZrO.sub.2, B.sub.2 O.sub.3125 Sialon + AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3 ZrO.sub.2126 Sialon + TiN ZrB.sub.2 + TiB.sub.2 ZrO.sub.2, Y.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.2127 Sialon + SiC ZrB.sub.2 + FeB.sub.2 ZrO.sub.2, Cr.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.2128 Si.sub.3 N.sub.4 + TiN FeB.sub.2 ZrO.sub.2, Cr.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3129 Si.sub.3 N.sub.4 + Mo AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3130 Sialon + Mo ZrB.sub.2 + TiB.sub.2 Zircon ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.2131 TiN ZrB.sub.2 + FeB.sub.2 ZrO.sub.2, Y.sub.2 O.sub.3 Fe.sub.2 O.sub.3, B.sub.2 O.sub.3, ZrO.sub.2132 BN AlB.sub.2 Al.sub.2 O.sub.3, TiO.sub.2 Al.sub.2 O.sub.3, B.sub.2 O.sub.3______________________________________
In these examples, it is important that the oxidizing rate of the self-recoverable layer is greater than that of the outermost surface layer. The effect of the self-recoverable layers of the present invention is not limited to the ceramics and C/C composites used in these examples, but may be applied to all of ceramics, C/C composites and metals.
In comparative examples, shown in Table 6, the oxidizing rate of the self-recoverable layer is less than that of the outermost surface layer. In such a covering structure, cracks generated on the outermost surface layer are temporarily recovered by the oxidizing reaction of the outermost surface layer; however, the essential recovering function cannot be obtained because the whole of the outermost surface layer is oxidized and eroded.
TABLE 6______________________________________Comparative Self-Recoverable Outermost RecoveredExample No. Structure Layer Surface Layer Product______________________________________1 Si.sub.3 N.sub.4 Al.sub.2 O.sub.3 ZrB.sub.2 None2 Si.sub.3 N.sub.4 Al.sub.2 O.sub.3 TiB.sub.2 None3 Si.sub.3 N.sub.4 SiC BN None4 SiC ZrO.sub.2 ZrB.sub.2 None______________________________________
EXAMPLES 133-155
The surface of each of the structures made of metals and alloys shown in Table 7 was covered with each self-recoverable layer shown in Table 7 to a thickness of 200 .mu.m, and an outermost surface layer made of each oxide shown in Table 7 to a thickness of 150 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost layer thus obtained were dense with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 150 .mu.m was given on the outermost surface of the structure. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C., while the interior of the structure was cooled by water. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air. Each component of the recovered portion was shown in Table 7.
From these examples, it becomes apparent that the self-recovering function of the present invention is not affected by a covering material. Structures to be covered may include ceramics, C/C composites, and metals and alloys.
TABLE 7__________________________________________________________________________ Self- Recoverable OutermostNo. Structure Layer Surface Layer Recovered Product__________________________________________________________________________133 Stainless Steel ZrB.sub.2 ZrO.sub.2 ZrO.sub.2,B.sub.2 O.sub.3134 Stainless Steel TiB.sub.2 TiO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, B.sub.2 O.sub.3135 Stainless Steel CaB.sub.2 CaO, ZrO.sub.2 CaO, B.sub.2 O.sub.3136 Cast iron WB WO.sub.2, Al.sub.2 O.sub.3 WO.sub.2, B.sub.2 O.sub.3137 Nb.sub.3 Al LaB.sub.2 La.sub.2 O.sub.3, Al.sub.2 O.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.3138 Ni alloy HfB.sub.2 HfO.sub.2, Al.sub.2 O.sub.3 HfO.sub.2, B.sub.2 O.sub.3139 Ni alloy TaB.sub.2 Ta.sub.2 O.sub.5, Al.sub.2 O.sub.3 Ta.sub.2 O.sub.5, B.sub.2 O.sub.3140 Cr alloy NbB.sub.2 Nb.sub.2 O.sub.5, Al.sub.2 O.sub.3 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3141 Carbon steel AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3142 Cr--Ni alloy ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3143 Cr--Ni alloy ZrB.sub.2 + AlB.sub.2 Al.sub.2 O.sub.3 ZrO.sub.2, Al.sub.2 O.sub.3144 Fee Cutting steel; ZrB.sub.2 + FeB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 FeO.sub.3, B.sub.2 O.sub.3, ZrO.sub.2145 Heat-resisting steel ZrB.sub.2 + TiB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.2146 Rolled steel NbB.sub.2 Nb.sub.2 O.sub.5, Al.sub.2 O.sub.3 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3147 Inconel NbB.sub.2 Nb.sub.2 O.sub.5, ZrO.sub.2 Nb.sub.2 O.sub.5, B.sub.2 O.sub.3148 Ni.sub.3 (Al, Ti) ZrB.sub.2 + TiB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, TiO.sub.2149 Fiber-reinforced Al AlB.sub.2 Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3150 SiC particle ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3 dispersion- strengthened Ti metal151 One-way eutectic TiB.sub.2 TiO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, B.sub.2 O.sub.3 alloy (Cr--TaC)152 Al alloy ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3153 Ti alloy ZrB.sub.2 ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3154 Al alloy ZrB.sub.2 ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3155 SiC particle dispersion- ZrB.sub.2 ZrO.sub.2, SiC ZrO.sub.2, B.sub.2 O.sub.3 strengthened Ti metal__________________________________________________________________________
EXAMPLES 156-164
The surface of each structure shown in Table 8 was covered with three or more layers including a self-recoverable layer having a thickness of 200 .mu.m, and an outermost surface layer having a thickness of 100 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost layer thus obtained were dense, with a porosity of 3% or less.
Each structure of the covering layers is shown in Table 8. Each layer such as the self-recoverable layer is dense, with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 100 .mu.m up to the self-recoverable layer was given on the outermost surface of the structure. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500 degrees C.
TABLE 8__________________________________________________________________________ Self-Recoverable Layer and Outermost RecoveredNo Structure Surface Layer Product__________________________________________________________________________156 Si.sub.3 N.sub.4 First layer: ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3 Second layer: ZrB.sub.2 self-recoverable layer Third layer: ZrO.sub.2157 Sialon First layer: Al.sub.2 O.sub.3, TiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3 Second layer: ZrB.sub.2 self-recoverable layer Third layer: ZrO.sub.2158 Sialon First layer: Al.sub.2 O.sub.3, TiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3 Second layer: Al.sub.2 O.sub.3 Third layer: ZrB.sub.2 self-recoverable layer Fourth layer: ZrO.sub.2159 Inconel First layer: Al.sub.2 O.sub.3, TiO.sub.2 Al.sub.2 O.sub.3, B.sub.2 O.sub.3 Second layer: AlB.sub.2 self-recoverable ZrO.sub.2, B.sub.2 O.sub.3 layer Third layer: Al.sub.2 O.sub.3 Fourth layer: ZrB.sub.2 self-recoverable layer Fifth layer: ZrO.sub.2160 SiC First layer:. Si.sub.3 N.sub.4 TiO.sub.2, B.sub.2 O.sub.3 Second layer: TiB.sub.2 self-recoverable ZrO.sub.2, B.sub.2 O.sub.3 layer Third layer: ZrB.sub.2 self-recoverable layer Fourth layer: ZrO.sub.2161 Sialon First layer: AlN Second layer: ZrB.sub.2 self-recoverable ZrO.sub.2, B.sub.2 O.sub.3 layer Third layer: ZrO.sub.2, Al.sub.2 O.sub.3162 Si.sub.3 N.sub.4 First layer: Ni alloy Nb.sub.2 O.sub.3, B.sub.2 O.sub.3 Second layer: NbB.sub.2 self-recoverable ZrO.sub.2, B.sub.2 O.sub.3 layer Third layer: ZrB.sub.2 self-recoverable layer Fourth layer: ZrO.sub.2163 Inconel First layer: Al.sub.2 O.sub.3, TiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3 Second layer: TiC Third layer: Al.sub.2 O.sub.3 Fourth layer: ZrB.sub.2 self-recoverable layer Fifth layer: ZrO.sub.2164 Nb.sub.3 Al First layer: Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3 Second layer: ZrB.sub.2 self-recoverable layer Third layer: ZrO.sub.2__________________________________________________________________________
EXAMPLES 165-173
Tests were made to examine what effect the difference in the thermal expansion coefficient between covering layers would exert on the self-recovering function.
The surface of each structure shown in Table 9 was covered with three or more layers including a self-recoverable layer having a thickness of 200 .mu.m, and an outermost surface layer having a thickness of 100 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost surface layer were dense, with a porosity of 3% or less. The structure of the covering layers is shown in Table 9. The structure thus covered was heated from room temperature to 500.degree. C. and then cooled by water. Thus, the structure was examined for the state of the interface between the covering layers.
As a result, it is revealed that when the difference in the thermal expansion coefficient between some covering layers including the self-recoverable layer is increased to be more than 4.times.10.sup.-6 /.degree.C., peeling is generated, which fails to achieve the self-recovering function with a high reliability. Accordingly, it is possible to obtain covering layers having a self-recovering function being excellent in the thermal shock resistance by controlling the thermal expansion coefficients between respective covering layers to be gradually changed.
TABLE 9__________________________________________________________________________ Self-Recoverable Layer and Outermost Surface Recovered Result ofNo. Structure Layer Product Test__________________________________________________________________________165 Si.sub.3 N.sub.4 Second layer: TiO.sub.2, B.sub.2 O.sub.3 Partial 3 .times. 10.sup.-6 /.degree.C. TiB.sub.2 (7.9 .times. 10.sup.-6 /.degree.C.) generation Third layer: of separation ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)166 Si.sub.3 N.sub.4 Second layer: ZrO.sub.2, B.sub.2 O.sub.3 Good 4 .times. 10.sup.-6 /.degree.C. ZrB.sub.2 (5.8 .times. 10.sup.-6 /.degree.C.) Third layer: ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)167 Sialon Second layer ZrO.sub.2, B.sub.2 O.sub.3 Good 3.2 .times. 1O.sup.-6 /.degree.C. ZrB.sub.2 (5.8 .times. 10.sup.-6 /.degree.C.) Third layer: ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)168 Si.sub.3 N.sub.4 Second layer: TiO.sub.2, B.sub.2 O.sub.3 Partial 3 .times. 10.sup.-6 /.degree.C. TiB.sub.2 (7.9 .times. 10.sup.-6 /.degree.C.) generation Third layer: of separation ZrO.sub.2, TiO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)169 Si.sub.3 N.sub.4 First layer: ZrO.sub.2, B.sub.2 O.sub.3 Good 3 .times. 10.sup.-6 /.degree.C. ZrB.sub.2 + Si.sub.3 N.sub.4 (4.0 .times. 10.sup.-6 /.degree.C.) Second layer: ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)170 Carbon steel First layer: TiO.sub.2, B.sub.2 O.sub.3 Good 12 .times. 10.sup.-6 /.degree.C. TiO.sub.2 (9.0 .times. 10.sup.-6 /.degree.C.) Second layer: TiB.sub.2 (7.9 .times. 10.sup.-6 /.degree.C.) Third layer: TiO.sub.2, ZrO.sub.2 (8.5 .times. 10.sup.-6 /.degree.C.)171 Carbon steel First layer: TiO.sub.2, B.sub.2 O.sub.3 Partial 12 .times. 10.sup.-6 /.degree.C. TiB.sub.2 (7.9 .times. 10.sup.-6 /.degree.C.) generation Second layer: of separation TiO.sub.2, ZrO.sub.2 (8.5 .times. 10.sup.-6 /.degree.C.)172 Stainless First layer: ZrO.sub.2, B.sub.2 O.sub.3 Good steel TiO.sub.2 (9.0 .times. 10.sup.-6 /.degree.C.) 13 .times. 10.sup.-6 /.degree.C. Second layer: ZrO.sub.2 (5.8 .times. 10.sup.-6 /.degree.C.) Third layer: ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)173 Stainless First layer: ZrO.sub.2, B.sub.2 O.sub.3 Partial steel TiB.sub.2 (7.9 .times. 10.sup.-6 /.degree.C.) generation 13 .times. 10.sup.-6 /.degree.C. Second layer of separation ZrB.sub.2 (5.8 .times. 10.sup.-6 /.degree.C.) Third layer: ZrO.sub.2 (8.0 .times. 10.sup.-6 /.degree.C.)__________________________________________________________________________
EXAMPLES 174-228
The surface of each structure shown in Table 10 was covered with each self-recoverable layer shown in Table 10 to a thickness of 200 .mu.m, and each outermost surface layer such as ZrO.sub.2 shown in Table 10 to a thickness of 200 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost layer thus obtained were dense with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the outermost surface of the structure. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500.degree. C. Each component of the recovered portion was shown in Tables 10 and 11.
TABLE 10__________________________________________________________________________ Self- Recoverable OutermostNo. Structure Layer Surface Layer Recovered Product__________________________________________________________________________174 Si.sub.3 N.sub.4 ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2175 Si.sub.3 N.sub.4 TiSi TiO.sub.2, ZrO.sub.2 TiO.sub.2, SiO.sub.2176 Si.sub.3 N.sub.4 MoSi ZrO.sub.2, SiO.sub.2 MoO, SiO.sub.2177 Si.sub.3 N.sub.4 FeSi ZrO.sub.2, SiO.sub.2 Fe.sub.2 O.sub.3, SiO.sub.2178 Si.sub.3 N.sub.4 CoSi ZrO.sub.2, SiO.sub.2 CoO.sub.2, SiO.sub.2179 Si.sub.3 N.sub.4 LaSi ZrO.sub.2, SiO.sub.2 La.sub.2 O.sub.3, SiO.sub.2180 Si.sub.3 N.sub.4 HfSi ZrO.sub.2, SiO.sub.2 HfO.sub.2, SiO.sub.2181 Si.sub.3 N.sub.4 TaSi ZrO.sub.2, SiO.sub.2 TaO.sub.2, SiO.sub.2182 Si.sub.3 N.sub.4 NbSi ZrO.sub.2, SiO.sub.2 Nb.sub.2 O.sub.5, SiO.sub.2183 Si.sub.3 N.sub.4 AlSi ZrO.sub.2, Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, SiO.sub.2184 Si.sub.3 N.sub.4 NiSi ZrO.sub.2, SiO.sub.2 NiO.sub.2, SiO.sub.2185 Si.sub.3 N.sub.4 ZrB.sub.2 + ZrSi ZrO.sub.2, SiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2186 Si.sub.3 N.sub.4 ZrSi + MoSi ZrO.sub.2, SiO.sub.2 ZrO.sub.2, SiO.sub.2, MoO187 Si.sub.3 N.sub.4 ZrSi + AlSi ZrO.sub.2, SiO.sub.2 ZrO.sub.2, SiO.sub.2, Al.sub.2 O.sub.3188 SiC AlSi Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, SiO.sub.2189 Mullite NiSi ZrO.sub.2, SiO.sub.2 NiO.sub.2, SiO.sub.2190 Sialon ZrB.sub.2 + Zrsi ZrO.sub.2, SiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2191 AlN ZrSi + MoSi ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, SiO.sub.2, MoO192 C/C composite ZrB.sub.2 + ZrSi ZrO.sub.2, SiO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2193 Sialon + SiC ZrB.sub.2 + ZrSi ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2194 Sialon + TiN ZrSi + B.sub.4 C ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3, SiC195 C/C composite AlSi Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, SiO.sub.2196 Sialon + ZrO.sub.2 ZrSi + MoSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, MoO197 Si.sub.3 N.sub.4 + SiC ZrSi + MoSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, MoO198 Si.sub.3 N.sub.4 + AlN TiB.sub.2 + ZrSi ZrO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2199 Si.sub.3 N.sub.4 + ZrO.sub.2 ZrB.sub.2 + ZrSi ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2200 Si.sub.2 N.sub.2 O ZrSi + B.sub.4 C ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3, SiC201 Si.sub.3 N.sub.4 + TiCN TiB.sub.2 + ZrSi ZrO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2202 Si.sub.3 N.sub.4 + TiN ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2203 Si.sub.3 N.sub.4 + Mo ZrB.sub.2 + ZrSi ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2204 Si.sub.3 N.sub.4 + WC TiB.sub.2 + ZrSi ZrO.sub.2 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2205 Sialon + WC ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3, SiC206 BN ZrB.sub.2 + ZrSi ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2207 TiN TiB.sub.2 + ZrSi ZrO.sub.2 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2208 TiC ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3, Si.sub.3 N.sub.4209 WC ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3,__________________________________________________________________________ SiC
TABLE 11__________________________________________________________________________ Self- Outermost RecoverableNo. Structure Layer Surface Layer Recovered Product__________________________________________________________________________210 Si.sub.3 N.sub.4 ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3, SiC211 Si.sub.3 N.sub.4 TiB.sub.2 + ZrSi ZrO.sub.2 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2212 Si.sub.3 N.sub.4 TiB.sub.2 + ZrSi ZrO.sub.2 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2213 C/C composite ZrSi Zircon ZrO.sub.2, SiO.sub.2214 Si.sub.3 N.sub.4 + SiC FeSi ZrO.sub.2, Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, SiO.sub.2215 Si.sub.3 N.sub.4 + ZrO.sub.2 ZrB.sub.2 + ZrSi ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2216 Si.sub.3 N.sub.4 + AlN ZrSi Zircon ZrO.sub.2, SiO.sub.2217 Si.sub.3 N.sub.4 + SiC TiSi ZrO.sub.2, SiO.sub.2 TiO.sub.2, SiO.sub.2218 AlN WSi WO.sub.2, TiO.sub.2 WO.sub.2, B.sub.2 O.sub.3, SiO.sub.2219 Mullite LaSi La.sub.2 O.sub.3, SiO.sub.3 La.sub.2 O.sub.3, B.sub.2 O.sub.3, SiO.sub.3220 Sialon HfSi HfO.sub.2, Y.sub.2 O.sub.3 HfO.sub.2, B.sub.2 O.sub.3, SiO.sub.3221 C/C composite TaSi ZrO.sub.2 + TaO.sub.2 TaO.sub.2, B.sub.2 O.sub.3, SiO.sub.2222 Si.sub.2 N.sub.2 O FeSi.sub.2 ZrO.sub.2, SiO.sub.2 Fe.sub.2 O.sub.3, SiO.sub.2223 Sialon + ZrO.sub.2 AlSi Al.sub.2 O.sub.3, MgO Al.sub.2 O.sub.3, B.sub.2 O.sub.3, SiO.sub.2224 Sialon + TiN ZrSi Zircon ZrO.sub.2, SiO.sub.2225 Sialon + SiC ZrB.sub.2 + ZrSi ZrO.sub.2, Al.sub.2 O.sub.3 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2226 Si.sub.3 N.sub.4 + TiN TiB.sub.2 + ZrSi ZrO.sub.2 TiO.sub.2, ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2227 Si.sub.3 N.sub.4 + Mo AlB.sub.2 Al.sub.2 O.sub.3, Y.sub.2 O.sub.3 Al.sub.2 O.sub.3, B.sub.2 O.sub.3228 Si.sub.3 N.sub.4 + WC TiSi TiO.sub.2, Al.sub.2 O.sub.3 TiO.sub.2, B.sub.2 O.sub.3, SiO.sub.2__________________________________________________________________________
EXAMPLES 229-244
The surface of each structure shown in Table 12 was covered with each self-recoverable layer shown in Table 12 to a thickness of 200 .mu.m, and each outermost surface layer such as ZrO.sub.2 shown in Table 12 to a thickness of 200 .mu.m by a powder type plasma spraying. The plasma spraying was performed by a method wherein plasma was generated using argon gas in a vacuum atmosphere. The self-recoverable layer and the outermost layer thus obtained were dense with a porosity of 3% or less. A crack having a width of 0.2 mm and a depth of 200 .mu.m was given on the outermost surface of the structure. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500 degrees C. Each component of the recovered portion was shown in Table 12.
TABLE 12______________________________________ Self- Outermost Recoverable Surface RecoveredNo. Structure Layer Layer Product______________________________________229 Stainless steel ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2230 Cast iron TiSi TiO.sub.2, ZrO.sub.2 TiO.sub.2, SiO.sub.2231 Nb.sub.3 Al MoSi ZrO.sub.2, SiO.sub.2 MoO, SiO.sub.2232 Ni alloy FeSi ZrO.sub.2, Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3, SiO.sub.2233 Cr alloy CoSi CoO.sub.2, ZrO.sub.2 CoO.sub.2, SiO.sub.2234 Carbon steel LaSi La.sub.2 O.sub.3, ZrO.sub.2 La.sub.2 O.sub.3, SiO.sub.2235 Cr--Ni alloy HfSi HfO.sub.2, ZrO.sub.2 HfO.sub.2, SiO.sub.2236 Tool steel TaSi Ta.sub.2 O.sub.5, ZrO.sub.2 TiO.sub.5, SiO.sub.2237 Al alloy NbSi Nb.sub.2 O.sub.5, ZrO.sub.2 Nb.sub.2 O.sub.5, SiO.sub.2238 Ti alloy AlSi Al.sub.2 O.sub.3, ZrO.sub.2 Al.sub.2 O.sub.3, SiO.sub.2239 Ni.sub.3 (Al, Ti) NiSi NiO.sub.2, ZrO.sub.2 NiO.sub.2, SiO.sub.2240 Inconel ZrB.sub.2 + ZrSi ZrO.sub.2 ZrO.sub.2, B.sub.2 O.sub.3, SiO.sub.2241 Fiber- ZrSi + MoSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, MoO reinforced Al242 One-way ZrSi ZrO.sub.2 ZrO.sub.2, SiO.sub.2, B.sub.2 O.sub.3 eutectic alloy Cr--TaC243 Free-cutting AlSi Al.sub.2 O.sub.3 Al.sub.2 O.sub.3, SiO.sub.2 steel244 SiC particle NiSi NiO.sub.2, ZrO.sub.2 NiO.sub.2, SiO.sub.2 dispersion- strengthened Ti metal______________________________________
EXAMPLE 245
The ceramic structures, self-recoverable layers, and outermost surface layers having the compositions shown in Examples 1 to 84, 156 to 158, and 162 were fabricated by a laminating method. A ceramic powder as a source of a structure having an average particle size of 0.5 .mu.m was dry-mixed by a mill (automatic mixer). The mixed powder was added with a specified amount of an organic solvent, being formed in a slurry, and was formed into a green sheet by a doctor blade method. Similarly, a ceramic source for a self-recoverable layer was formed into a green sheet by the doctor blade method. Moreover, a ceramic source for an outermost surface layer was formed into a green sheet by the doctor blade method. These green sheets were laminated, and then compressed with a pressure of 98 MPa in the laminating direction into a compact. The compact thus obtained was heated in an inert gas at a temperature ranging from 1400.degree. to 2100.degree. C. until it was densified, thus fabricating a structure covered with the self-recoverable layer (FIG. 3). A crack having a width of 0.3 mm was given on the outermost surface of the structure up to a depth of the self-recoverable layer. The structure was then kept for 100 hr. in the atmospheric air at 1500.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500.degree. C.
EXAMPLE 246
The self-recoverable layers and the outermost surface layers shown in Examples 1 to 132 were covered by a CVD (Chemical Vapor Deposition) process. For example, a structure was disposed in a reaction chamber, and a titanium halide gas and a boron halide gas were introduced in the reaction chamber at 1000.degree. C., to thus cover the surface of the structure with TiB.sub.2. Similarly, by changing the component of an introduced gas and the temperature of the reaction chamber, it is possible to cover the surface of the structure with the layer having each composition shown in the above-described examples. The covering layer thus obtained was dense with a porosity of 5% or less. A crack having a width of 0.3 mm was given on the outermost surface of the structure up to a depth of the self-recoverable layer. The structure was then kept for 1000 hr. in the atmospheric air at 1200.degree. C. As a result, the cracked portion was recovered by a product material generated by the reaction between the self-recoverable layer and oxygen in the atmospheric air at 1500 degrees C.
From this example, it is revealed that the self-recovering function of the present invention is not affected by the covering method. The covering methods include, other than the laminating method, the conventional known methods such as a covering method, printing method, PVD process, CVD process, electrophoresis method, and spraying method. The detail of the covering method is shown, for example, in "Ceramic Covering Technique" issued by General Technical Center.
EXAMPLES 247-254
To examine what effect the thickness of a covering layer exerts on the self-recovering function, tests were made for the structures shown in Example 1. The result is shown in Table 13. As is apparent from Table 13, the thickness of the self-recoverable layer is required to be at least 1/10 that of the outermost surface covering layer for sufficiently achieving the self-recovering function.
TABLE 13______________________________________ Thickness of Thickness of Self-Recoverable Outermost RecoveredNo. Structure Layer Surface Layer Product______________________________________247 Si.sub.3 N.sub.4 ZrB.sub.2 (150 .mu.m) ZrO.sub.2 (200 .mu.m) Good248 Si.sub.3 N.sub.4 ZrB.sub.2 (100 .mu.m) ZrO.sub.2 (200 .mu.m) Good249 Si.sub.3 N.sub.4 ZrB.sub.2 (80 .mu.m) ZrO.sub.2 (200 .mu.m) Good250 Si.sub.3 N.sub.4 ZrB.sub.2 (50 .mu.m) ZrO.sub.2 (200 .mu.m) Good251 Si.sub.3 N.sub.4 ZrB.sub.2 (40 .mu.m) ZrO.sub.2 (200 .mu.m) Good252 Si.sub.3 N.sub.4 ZrB.sub.2 (20 .mu.m) ZrO.sub.2 (200 .mu.m) Good253 Si.sub.3 N.sub.4 ZrB.sub.2 (10 .mu.m) ZrO.sub.2 (200 .mu.m) Unusable for a long time254 Si.sub.3 N.sub.4 ZrB.sub.2 (5 .mu.m) ZrO.sub.2 (200 .mu.m) Unusable for a long time______________________________________
EXAMPLE 255
A moving blade and a stator blade for a gas turbine shown in FIGS. 4 and 5 were fabricated using the members obtained in Examples 1, 16, 85, and 156 to 163. A gas turbine of a class of 1500.degree. C., which was incorporated with the member, was operated; and periodically stopped to examine the state of surface damage. There was no abnormality until 1000 hr, and cracks were generated after 2000 hr; however, the cracked portion was self-recovered by a compound produced from the self-recoverable layer. Even after 5000 hr, the cracks were buried by the self-recoverable layer, thereby preventing the oxidization of the structure as the base material.
EXAMPLE 256
A structural member, in which the surface of a Si.sub.3 N.sub.4 structure was covered with AlB.sub.2 as a self-recoverable layer and sialon was covered on the outermost surface, was applied to a roll shaft used for continuous hot dip zinc plating. FIG. 6 shows a continuous hot dip zinc plating apparatus. The member was used for a roll shaft 8 and a support roll 10 in FIG. 6. A C/C composite was used for a bearing 9. The apparatus in this example was used for continuous plating in a zinc bath at 500.degree. C. The sialon layer was worn after 1000 hr; however, the damaged portion was recovered by the intermetalic compound of Al--Zn produced by the reaction between AlB.sub.2 as the self-recoverable layer and zinc.
The service life of a conventional steel roll shaft and bearing due to wear was three days. However, the member in this embodiment did not suffer from abnormal wear even after continuous operation for three months or more, contributing to the uniform plating work.
As shown in this example, a product material generated by the reaction between molten metal in a service environment and a self-recoverable layer can achieve the recovering function.
EXAMPLE 257
A structural member, in which the surface of a Si.sub.3 N.sub.4 structure was covered with NbB.sub.2 as a self-recoverable layer and sialon was covered on the outermost surface, was applied to a roll shaft for continuous hot dip aluminum plating. The member was used for a roll shaft 8 and a support roll 10 in FIG. 6. A C/C composite was used for a bearing 9. The apparatus in this example was used for continuous plating in an aluminum bath at 680.degree. C. The sialon layer was worn after 1000 hr; however, the damaged portion was recovered by the intermetalic compound of Nb--Al produced by the reaction between NbB.sub.2 as the self-recoverable layer and aluminum. The service life of a conventional steel roll shaft and bearing was four days. However, the member in this embodiment did not suffer from abnormal wear even after continuous operation for three months or more, contributing to the uniform plating work.
EXAMPLE 258
A metal Si powder having an average particle size of 1 .mu.m (100 parts by weight) was added with a mixture of polyethylene, stearic acid and synthetic wax (13 parts by weight), and then kneaded, to form a source as a ceramic part. The source was extruded into a plate having a size of 100.times.100.times.10 mm by an extruder. A bundle (diameter: 1.5 mm) of carbon fibers (diameter: 10 .mu.m, length: 1000 .mu.m) was molded on this plate, to form a resistance measuring circuit for life diagnosis.
The compact was heated up to 1350.degree. C. with a temperature rising rate of 1.degree. C./min, and cooled in a furnace, to obtain a Si.sub.3 N.sub.4 reaction-sintered ceramic having a resistance measuring circuit for life diagnosis. The degreasing for a binder was performed in the temperature rising process. The surface layer portion of the reaction-sintered ceramic thus obtained was covered with ZrB.sub.2 as a self-recoverable layer to a thickness of 200 .mu.m by plasma spraying. A dense film of ZrO.sub.2 was formed thereon to a thickness of 200 .mu.m for ensuring the heat resistance by plasma spraying. In the reaction-sintered body, since the surface layer portion was porous and ZrB.sub.2 was produced in voids, a film with a high bonding strength could be obtained. A copper wiring was brazed to the end portion of the inner circuit, which was connected to an external measuring apparatus.
The ceramic part was applied to a lining part in a combustor for a 1500.degree. C. class gas turbine. As a result, in the ceramic part, when the ZrO.sub.2 film was broken by a combustion test, ZrB.sub.2 was simultaneously oxidized to recover the ZrO.sub.2 film. At the same time, the resistance of the resistance measuring circuit for life diagnosis changed. The changed resistance was compared with a threshold for performing life diagnosis for the lining part in the combustor (FIG. 7).
Similarly, a complex ceramic (Si.sub.3 N.sub.4 /Si.sub.2 N.sub.2 O, Si.sub.3 N.sub.4 /AlN, Si.sub.3 N.sub.4 /Al.sub.2 O.sub.3, Si.sub.3 N.sub.4 /ZrO.sub.2, Si.sub.3 N.sub.4 /mullite, Si.sub.3 N.sub.4 /SiC or the like) having a resistance measuring circuit for life diagnosis was fabricated by the reaction sintering method using the above Si powder mixed with powders or whiskers of Si.sub.3 N.sub.4, Si.sub.2 N.sub.2 O, AlN, Al.sub.2 O.sub.3, ZrO.sub.2, B.sub.4 C, BN, mullite and the like. The complex ceramic thus obtained was applied to the lining part in the combustor, which gave the same result as the above-described ceramic part, that is, which achieved the life diagnosis by the excellent self-recovering function.
The formation of the ceramics used in the present invention may be performed by methods of doctor blade, die compacting, CIP, injecting molding, slip-casting, extrusion and the like according to the shapes of the parts.
As the binder for molding the above-described green sheet, there may be used known binders for molding ceramics, which include high polymer materials such as polyvinyl butyryl and polyethylene, silicone-family compounds, and polysilane-family compounds. The degreasing method for these binders is not limited, but it is preferably performed by controlling the temperature rising rate during sintering.
EXAMPLE 259
Powders of ZrO.sub.2 (50 parts by weight), SiO.sub.2 (30 parts by weight), Al.sub.2 O.sub.3 (20 parts by weight) were mixed with triethanol amine (1 part by weight) and distilled water (65 parts by weight), to form a source for a ceramic part. Using the source thus obtained, there were fabricated, by slip casting, a tonguedish for molten metal, a refractory for mold inlet, and a mold. In molding, a bundle of carbon fibers (diameter: 100 .mu.m, length: 50 cm, number: 100) were inserted in each member, to form a resistance measuring circuit for life diagnosis.
The above molded product was heated up to 1650.degree. C. with a temperature rising rate of 5.degree. C./min in an oxidizing atmosphere, being kept for 2 hr, and was cooled in a furnace, thus obtaining a ceramic having a resistance measuring circuit for life diagnosis. The degreasing for a binder was performed in the temperature rising process. The end portion of the life diagnosis circuit was connected to an external circuit by way of a copper wiring. Moreover, the life diagnosis circuit was insulated by an Al.sub.2 O.sub.3 protecting tube.
The surface layer portion of the ceramic thus obtained was covered with LaB.sub.2 as a self-recoverable layer by plasma spraying, and a dense film of sialon was formed thereon to a thickness of 200 .mu.m for ensuring a heat resistance by plasma spraying.
The ceramic parts were applied to an aluminum continuous casting machine. As a result of the testing, when each ceramic part was worn out and cracked, the cracked portion was recovered by a LaAl layer and simultaneously the resistance was changed. The change in the resistance was detected, to give the life of the part to an operator. This makes it possible to effectively perform the maintenance of the continuous casting machine.
EXAMPLE 260
An outer wall tile and nose cone for a space shuttle were fabricated using the inventive members obtained in Examples. 85, 94 and 95. The members were subjected to a burner test at 2000.degree. C., and the equipment was periodically stopped to examine the damaged state on the surface. There was no abnormality until 50 hr, and cracks were generated at the ZrO.sub.2 layer after 100 hr; however, the cracked portion was recovered by a product material generated from the self-recoverable layer, thus preventing the oxidization of the structure as the base material.
EXAMPLE 261
Using oxides produced from the self-recoverable layers, other than those shown in the above-described examples, have also the self-recovering function. For example, when the oxides shown in Table 14 were used in environments having temperature lower than the melting points thereof, there could be obtained the stable recovered portions. In particular, a Al.sub.2 O.sub.3 system and MgO system are stable. As the self-recoverable layers, borides and silicates capable of producing the compounds shown in Table 14 by oxidization may be selected.
TABLE 14______________________________________Recovered Product from Self- Recovered Product from Self-Recoverable Layer and Melting Recoverable Layer and Melting PointPoint (.degree.C.) (.degree.C.)______________________________________Al.sub.2 O.sub.3 --BaO 1425 Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 1400Al.sub.2 O.sub.3 --BeO 1835 K.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 1686Al.sub.2 O.sub.3 --CaO 1400 MgO--Al.sub.2 O.sub.3 --SiO.sub.2 1470Al.sub.2 O.sub.3 --CeO.sub.2 1800 CaO--Al.sub.2 O.sub.3 --SiO.sub.2 1553Al.sub.2 O.sub.3 --FeO 1310 BaO--Al.sub.2 O.sub.3 --SiO.sub.2 1750Al.sub.2 O.sub.3 --MgO 1995 FeO--Al.sub.2 O.sub.3 --SiO.sub.2 1560Al.sub.2 O.sub.3 --MnO 1520 CaO--MgO--SiO.sub.2 1500Al.sub.2 O.sub.3 --Na.sub.2 O 1410 CaO--TiO.sub.2 --SiO.sub.2 1352Al.sub.2 O.sub.3 --SiO.sub.2 1595 BaO--TiO.sub.2 --SiO.sub.2 1400Al.sub.2 O.sub.3 --TiO.sub.2 1705 CaO--ZrO.sub.2 --SiO.sub.2 1453Al.sub.2 O.sub.3 --ZnO 1700 .beta.-Spodumene 1000Al.sub.2 O.sub.3 --ZrO.sub.2 1885 Barium Osumilite 1250MgO--CaO 2370 Mullite 1500MgO--SiO.sub.2 1543 Hexacelsian 1700MgO--TiO.sub.2 1583 MgO--GeO.sub.2 1099MgO--ZrO.sub.2 1500 ZrO.sub.2 --SiO.sub.2 1687ZrO.sub.2 --TiO.sub.2 1760 ZrO.sub.2 --Nb.sub.2 O.sub.5 1430SiO.sub.2 --BaO 1370 SiO.sub.2 --CaO 1436SiO.sub.2 --SrO 1358 SiO.sub.2 --TiO.sub.2 1550SiO.sub.2 --ZnO 1432 TiO.sub.2 --BaO 1317______________________________________
Moreover, the compounds shown in Table 14 may be used as they are. In this case, the environmental temperature must be lower than the melting points of the self-recoverable layers.
A barrier may be inserted between the surface of a structure of a ceramic or C/C composite and a self-recoverable layer, as needed.
According to further embodiments of the invention the self-recoverable layer of the present invention can be formed into a complex shape, and therefore, it is easily applied to parts required for high reliability (for example, engine parts, parts for a continuous metal plating apparatus, first wall parts of a nuclear fusion reactor in an atomic power plant, moving blade and stator blade of a gas turbine, parts for combustor, shroud parts and the like).

Number	Name	Date
4399168	Kullander et al.	Aug 1983
5035923	Sarin	Jul 1991
5290354	Haluska	Mar 1994
5338577	Burdette	Aug 1994

Self-recoverable covering material and method for fabricating the same

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