Patent Application
20120134615
The present invention relates to a high-temperature axle bearing, and more particularly to a high-temperature axle bearing made of an intermetallic compound alloy containing Ni3(Si, Ti) as a basic composition (hereinafter referred to as Ni3(Si, Ti)-based intermetallic compound alloy”), and a method for producing the same.
Axle bearings are mechanical elements used in many industrial fields, and they are also used in a machine, such as a turbine or an engine, which requires an operation at high temperature. An axle bearing used under high temperature is made of a material such as a martensite stainless steel or a heat-resistant steel for an axle bearing. The upper limit temperature for a satisfactory operation of this type of axle bearing is about 300-400° C. Therefore, research and development for an axle bearing that can operate at high temperature have been made. As an axle bearing having a long life even under a high-temperature special environment, there has been known an axle bearing having rolling elements, wherein a base material of the rolling elements is a bearing steel or stainless steel, and a nitride process is performed on its surface (see, for example, Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication No. 2002-221227
Recently, axle bearings that can operate even at high temperature are demanded in a manufacturing domain of a semiconductor device or a liquid crystal, or in industrial facilities with heat treatment. Axle bearings having excellent property under high-temperature environment are demanded, and further, axle bearings having excellent life are demanded.
The present invention is accomplished in view of the foregoing circumstance, and aims to provide an axle bearing having excellent life under high temperature.
The present invention provides a high-temperature axle bearing made of an Ni3(Si, Ti)-based intermetallic compound alloy, wherein the Ni3(Si, Ti)-based intermetallic compound alloy contains from 25 to 500 ppm by weight of B with respect to a total weight of a composition of 100 at. % containing Ni as a major component, from 7.5 to 12.5 at. % of Si, from 4.5 to 10.5 at. % of Ti, from 0 to 3 at. % of Nb, and from 0 to 3 at. % of Cr, and has a Vickers hardness from 210 to 280 at 800° C.
Generally, hardness of materials decreases with increasing temperature. With this knowledge, the inventors of the present invention have considered that a material having excellent hardness at room temperature is not always suited as a material for an axle bearing having long life at high temperature, and they have earnestly made studies. As a result, they have found that an axle bearing, which is made of Ni3(Si, Ti)-based intermetallic compound alloy (hereinafter referred to as “intermetallic compound”) containing from 7.5 to 12.5 at. % of Si, from 4.5 to 10.5 at. % of Ti, from 0 to 3 at. % of Nb, and from 0 to 3 at. % of Cr, has excellent life at high temperatures such as 400° C.-800° C., thus completing the present invention. The axle bearing according to the present invention can well be used at high temperature.
a) is an X-ray diffraction profile of the embodiment sample 1 (as-cast material) that does not undergo the homogenization heat-treatment, and (b) is an X-ray diffraction profile of the embodiment sample 1 (homogenization-heat-treated material) that undergoes the homogenization heat-treatment for 48 hours at 1050° C.
a) is a top view of a rolling life test piece used for the thrust rolling life testing machine, and (b) is a sectional view of the same.
A high-temperature axle bearing according to one embodiment of the present invention is made of an Ni3(Si, Ti)-based intermetallic compound alloy, wherein the Ni3(Si, Ti)-based intermetallic compound alloy contains from 25 to 500 ppm by weight of B with respect to the total weight of the composition of 100 at. % containing Ni as a major component, from 7.5 to 12.5 at. % of Si, from 4.5 to 10.5 at. % of Ti, from 0 to 3 at. % of Nb, and from 0 to 3 at. % of Cr.
The content of each composition will firstly be described in detail. In the present specification, “from A to B” means that numerical values A and B are included in the range.
The content of Si is from 7.5 to 12.5 at. %, and more preferably from 10.0 to 12.0 at. %. The specific content of Si is, for example, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, or 12.5 at. %. The Si content may take a value between any two values of the aforementioned specific values.
The content of Ti is from 4.5 to 10.5 at. %, and more preferably, from 5.5 to 9.5 at. %. The specific content of Ti is, for example, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0 or 9.5 at. %. The Ti content may take a value between any two values of the aforementioned specific values.
Nb and Cr have characteristic of enhancing mechanical property at high temperature. Therefore, either one of Nb and Cr is preferably contained. The content thereof is preferably from 1.5 to 2.5 at. %. Both of Nb and Cr may be contained, and the content thereof may be from 1.5 to 2.5 at. %.
The content of Nb is from 0 to 3 at. %, and more preferably, from 1.5 to 2.5 at. %. The specific content of Nb is, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 at. %. The Nb content may take a value between any two values of the aforementioned specific values.
The content of Cr is from 0 to 3 at. %, and more preferably, from 1.5 to 2.5 at. %. The specific content of Cr is, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 at. %. The Cr content may take a value between any two values of the aforementioned specific values.
The content of Ni is from 78.5 to 81.0 at. %, and more preferably, from 78.5 to 80.5 at. %. The specific content of Ni is, for example, 78.5, 79.0, 79.5, 80.0, 80.5, or 81.0 at. %. The Ni content may take a value between any two values of the aforementioned specific values.
The content of each element is appropriately adjusted such that the total of the contents of Si, Ti, Nb, Cr, and Ni becomes 100 at. %.
The content of B is from 25 to 500 ppm by weight, more preferably, from 25 to 100 ppm by weight. The specific content of B is, for example, 25, 40, 50, 60, 75, 100, 150, 200, 300, 400, or 500 ppm by weight. The B content may take a value between any two values of the aforementioned specific values.
The specific composition of the intermetallic compound used for the high-temperature axle bearing according to the present embodiment is obtained by adding B in the above-mentioned content to the compositions shown in Tables 1 to 3 (or the compositions within the range between two of the compositions in Tables 1 to 3.)
Although the Vickers hardness of Ni3(Si, Ti)-based intermetallic compound alloy that forms the high-temperature axle bearing according to one embodiment of the present invention is not particularly limited, the Vickers hardness at 800° C. is preferably from 210 to 280. More specifically, it is, for example, 210, 220, 230, 240, 250, 260, 270, or 280. The Vickers hardness at 800° C. may take a value between any two values of the aforementioned specific values.
The Vickers hardness at 600° C. is preferably from 300 to 360. More specifically, it is, for example, 300, 310, 320, 330, 340, 350, or 360. The Vickers hardness at 600° C. may take a value between any two values of the aforementioned specific values.
The Vickers hardness at 500° C. is preferably from 370 to 400. More specifically, it is, for example, 370, 380, 390, or 400. The Vickers hardness at 500° C. may take a value between any two values of the aforementioned specific values. The hardness may take a value between any two values of the aforementioned specific values.
The Vickers hardness at room temperature is preferably from 370 to 400. More specifically, it is, for example, 370, 380, 390, or 400. The Vickers hardness at room temperature may take a value between any two values of the aforementioned specific values. The hardness may take a value between any two values of the aforementioned specific values.
The Vickers hardness of Ni3(Si, Ti)-based intermetallic compound alloy may only be not less than some value, and an axle bearing may be made of Ni3(Si, Ti)-based intermetallic compound alloy having Vickers hardness exceeding 280 at 800° C., for example. This is similarly applied to the other temperatures. The Vickers hardness at 600° C. may be larger than 360, and the Vickers hardness at 500° C. may be larger than 400. The Vickers hardness at room temperature may be larger than 400. As described above, the axle bearing may be made of Ni3(Si, Ti)-based intermetallic compound alloy having Vickers hardness larger than the described numerical values.
The difference between the Vickers hardness at room temperature and the Vickers hardness at 800° C. is not particularly limited, but it is preferably from 50 to 200. Specifically, it is, for example, 50, 100, 150, 190, or 200. This difference may take a value between any two values of the aforementioned specific values.
The microstructure of the Ni3(Si, Ti)-based intermetallic compound alloy will next be described. The intermetallic compound alloy used for the high-temperature axle bearing according to the present embodiment preferably contains a single-phase microstructure including an L12 phase, or a microstructure including an L12 phase and a Ni solid solution phase. If a hard secondary phase such as Ni3Nb is dispersed, the portion where the hard secondary phase is present is easy to be peeled or cracked. Therefore, the intermetallic compound alloy having a single phase of the L12 phase or having a phase such as the Ni solid solution phase, which has almost the same hardness as the matrix, may be preferable for forming the axle bearing. The L12 phase is Ni3(Si, Ti) phase into which Nb is solidly dissolved, and the Ni solid solution phase has an fcc structure, wherein a lattice constant thereof is almost equal to that of the L12 phase.
From the viewpoint of the Vickers hardness, the single-phase microstructure including the L12 phase is preferable. On the other hand, from the viewpoint of productivity and processability of the axle bearing, the microstructure including the L12 phase and the Ni solid solution phase is preferable. From the viewpoint of uniformity in the microstructure or in the deformation, the L12 phase is more preferable than the Ni solid solution phase. Accordingly, the single-phase microstructure including the L12 phase is preferable from the viewpoint of the deformation of the axle bearing and the dimensional accuracy.
The axle bearing according to the present invention may be a roll bearing or a slide bearing. The axle bearing is not particularly limited, so long as it is a roll bearing or a slide bearing. It may be a ball bearing, roller bearing, journal bearing, radial bearing, or thrust bearing, for example.
A slide bearing will be taken as one embodiment. The portion (e.g., a sliding surface) supporting an axis of the bearing is made of the Ni3(Si, Ti)-based intermetallic compound alloy. The portion supporting the axis of the bearing is made of a material that can retain hardness at high temperature. Therefore, the bearing according to the present invention has a configuration difficult to be worn, and hence, it has an excellent life.
A roll bearing will be taken as another embodiment. The bearing according to another embodiment has an inner ring, an outer ring, and rolling elements that roll between the inner ring and the outer ring. The rolling elements are made of a ceramic material, and at least either one (i.e., one or both) of the inner ring and the outer ring is made of the Ni3(Si, Ti)-based intermetallic compound alloy. In the bearing according to the present embodiment, the inner ring, the outer ring, and the rolling elements are made of a material that can retain hardness at high temperature. Therefore, like the bearing according to the above-mentioned embodiment, the bearing according to the present invention has a configuration difficult to be worn, and hence, it has an excellent life. Specifically, a raceway component such as the inner ring or the outer ring is preferably made of the Ni-based intermetallic compound alloy, and the rolling elements are preferably made of the ceramic material. The raceway component means a raceway ring provided with a raceway surface or raceway groove. In the roll bearing, for example, the inner ring and the outer ring correspond to the raceway component, and in the thrust bearing, a raceway washer corresponds to the raceway component.
For example, silicon nitride is preferable for the ceramic material. The other examples of the ceramic material may include silicon carbide, alumina (aluminum oxide), or zirconia (zirconium oxide). The ceramic material is preferable for the rolling elements, because it has small linear expansion coefficient, and it hardly causes adhesion or damage. When the rolling elements are formed from the ceramic material, the axle bearing having the excellent life can be provided.
The axle bearing according to one embodiment of the present invention can well be used at high temperature. The high-temperature axle bearing indicates an axle bearing used at temperature within the range of 400° C. to 800° C. Specific values of the temperature are, for example, 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., and 800° C. The temperature may take a value between any two values of the aforementioned specific values.
From the viewpoint of the Vickers hardness, the bearing may preferably be used at 500° C. or higher, and more preferably, used at 600° C. or higher. The axle bearing can more preferably be used at 500° C. or higher, compared to SUS630 (Fe-17Cr-4Ni-4Cu-0.35Nb). The axle bearing can more preferably be used at 600° C. or higher, compared to SUS440 C (Fe-18Cr-1C).
From the viewpoint of the material of the Ni3(Si, Ti)-based intermetallic compound, the maximum operating temperature is preferably 800° C. or less.
An ingot of the Ni3(Si, Ti)-based intermetallic compound alloy that forms the axle bearing is produced. For example, raw metals of the respective elements are prepared with the composition in the above-mentioned embodiment. Thereafter, they are melted in a melting furnace, put in a mold, and solidified. With this process, the ingot having the microstructure comprised of the L12 phase, or the microstructure comprised of the L12 phase and the Ni solid solution phase is prepared. From the viewpoint of strength at high temperature and uniformity in deformation, it is preferable that a heat treatment is further performed to the cast ingot. The heat treatment (homogenization heat-treatment) is performed to remove inhomogeneous solidified microstructure, and the condition thereof is not particularly limited. For example, the ingot may undergo the heat treatment in vacuum from 950 to 1100° C. for 24-48 hours. With this heat treatment, solidification strain due to a solidification rate, or inhomogeneity in a cast structure caused in a large-sized ingot can be overcome. The Ni solid solution phase with fcc structure can be reduced, so that the Vickers hardness can be enhanced. Accordingly, the material for the axle bearing having more excellent life can be provided.
Next, the prepared ingot of the intermetallic compound alloy is processed into a predetermined shape so as to form an axle bearing. For example, the prepared ingot is cut, and the cutting work is carried out, whereby an axle bearing with a predetermined shape is formed. Here, the ingot is cut, and the cutting work is carried out. However, this is only illustrative, and the invention is not limited to the cutting work. For example, a known process, such as a plastic working, can appropriately be used. Alternatively, the ingot may directly be shaped into the inner ring or the outer ring by a method of directly melting and casting the ingot into the shape of the inner ring or the outer ring, or a powder metallurgy process.
Finally, the axle bearing is assembled by using the inner ring, the outer ring, and the rolling elements. The rolling elements may be selected and acquired from those having a size corresponding to a predetermined gap between the inner ring and the outer ring.
The heat treatment may be performed after the formed ingot is cut, and the cutting work is carried out.
The embodiment of the present invention will next be described with reference to the drawings.
The holder 5 is preferably made of a material having a lubrication action. For example, graphite, soft metal, ceramic, or a composite of these materials, is preferable.
Various features shown in the above-mentioned embodiments can be combined to one another. When one embodiment includes plural features, one or plural features are appropriately extracted, and the extracted one feature can solely applied to the present invention, or the extracted plural features can be combined and applied to the present invention.
A performance test of the present invention will next be described. In the following test, a sample made of the Ni3(Si, Ti)-based intermetallic compound alloy having the composition shown in the above-mentioned embodiment, and a sample made of SUS440C that is a hard material exhibiting the highest hardness out of stainless steels were employed. For both samples, a mechanical property, a rolling fatigue life test, and a heat-resistant rotation test were carried out to evaluate these samples, in order to verify that the high-temperature axle bearing according to the present invention has excellent property at high temperature.
A sample made of an intermetallic compound was formed with the process described below.
Raw metals of Ni, Si, Ti, and Nb (each having a purity of 99.9 wt. %) and B were weighed to have the composition shown in Table 4. An ingot with 78φ×280 mm (about 11 kg) was formed as the sample containing Nb by a vacuum induction melting (VIM) process, while an ingot with a thickness of 10 mm was formed as the sample not containing Nb by an arc melting process. A melting chamber for the arc melting process was firstly evacuated, and then, the atmosphere in the melting chamber was replaced with an inert gas (argon gas). Non-consumable tungsten electrodes were used as electrodes of the furnace, and a water-cooling copper hearth was employed as a mold. The homogenization heat-treatment was performed to the sample not containing Nb in order to eliminate cast segregation and to be homogenized. During the homogenization process, a vacuum heat treatment (furnace cool) was performed in which the sample was retained at 1050° C. for 48 hours.
The sample containing Nb is the Ni3(Si, Ti)-based intermetallic compound alloy that is the material used in the embodiment of the present invention, and it will be referred to as “embodiment sample 1” below. The sample not containing Nb is one example of the Ni3(Si, Ti)-based intermetallic compound alloy that is the material used for the axle bearing of the present invention, and it will be referred to as “embodiment sample 2” below.
The ingot of the embodiment sample 1 was cut into a predetermined thickness. The cutting work was performed to the obtained disk material, whereby an inner ring and an outer ring of the bearing were produced. A rough grinding process was performed to the inner diameter, outer diameter, and end face, and then, a super finishing grinding process that was the final finish was performed to the raceway surfaces of the inner ring and the outer ring.
A silicon-nitride-ceramic ball was assembled in order that the produced inner ring and the outer ring were arranged with a predetermined gap. A solid lubricant holder was attached. Thus, the ball bearing shown in
The sectional structure of the ingot of the embodiment sample 1 was evaluated.
In order to eliminate the cast segregation and attain homogenized microstructure, the homogenization heat-treatment was performed to the embodiment sample 1, and then, the microstructure was observed.
a) is an SEM photograph of the embodiment sample 1 to which the vacuum heat-treatment (furnace cool) has not been performed.
a) shows the result of the X-ray diffraction (XRD) measurement of the embodiment sample 1 to which the homogenization heat-treatment has not been performed, while
It is found from
As is apparent from
The inventors have found that the Ni solid solution phase same as that described above appears even in the Ni3(Si, Ti) alloy containing excessive Ni, and the Ni solid solution phase disappears when the Ni3(Si, Ti) containing excessive Ni is subjected to a low-temperature heat-treatment. Therefore, the temperature for the heat-treatment was dropped to 950° C. from 1050° C., and then, the change in the microstructure was observed.
It is found from
The Vickers hardness test was carried out at high temperature (300° C., 500° C., 600° C., and 800° C.) for the embodiment sample 1, the embodiment sample 2, and the embodiment sample 1 to which the vacuum heat-treatment (furnace cool) for 48 hours at 950° C. was performed. The Vickers hardness test at high temperature was simultaneously carried out for two materials that were SUS440C and SUS630. The SUS440C was subjected to the Vickers hardness test at high temperatures of 300° C., 500° C., and 800° C., while the SUS630 was subjected to the Vickers hardness test at high temperatures of 300° C., 500° C., 600° C., and 800° C. The load was 1 kg, and the retention time was 20 seconds. The measurement was carried out in a reduction atmosphere (Ar+about 10% H2), and the rate of temperature rise was 10° C. per minute. Prior to the measurement at high temperatures, the Vickers hardness of a test piece, which was the same as that used for the high-temperature Vickers hardness test, at room temperature was measured under the same measurement conditions (load: 1 kg, retention time: 20 seconds).
It is understood from
For example, in
It is also found that the Vickers hardness of the embodiment sample 1, the embodiment sample 2, and the embodiment sample 1 to which the vacuum heat-treatment (furnace cool) for 48 hours at 950° C. was performed are higher than the Vickers hardness of the SUS630 in the temperature region of 500° C. or more. It is also found that the Vickers hardness of the sample to which the homogenization heat-treatment has been performed is higher than the Vickers hardness of the SUS440C at 600° C. or more.
In light of the environment where the axle bearing is used, it is considered that the alloy such as the SUS440C is deteriorated at high temperature due to oxidation, or the microstructure thereof is changed or becomes coarse. Therefore, when the axle bearing is formed from such material, it can be supposed that the advantages of the embodiment samples appear in the lower temperature region.
It is also found that the Vickers hardness of the embodiment sample 2, and the embodiment sample 1 to which the vacuum heat-treatment (furnace cool) for 48 hours at 950° C. was performed are higher than the Vickers hardness of the embodiment sample 1. This is because the embodiment sample 1 (as-cast material) contains many Ni solid solution phases. From the viewpoint of the hardness at high temperature, the microstructure comprised of only L12 single phase is supposed to be desirable.
As can be understood from
On the other hand, the Vickers hardness of the ingot of the embodiment sample 1 formed by the vacuum induction process was about 400 at room temperature, about 390 at 300° C., about 370 at 500° C., about 300 at 600° C., and about 210 at 800° C., and the Vickers hardness of the embodiment sample 1 to which the vacuum heat-treatment (furnace cool) for 48 hours at 950° C. was performed was about 370 at room temperature, about 400 at 300° C., about 370 at 500° C., about 350 at 600° C., and about 280 at 800° C. The Vickers hardness of the embodiment sample 2 was about 370 at room temperature, about 380 at 300° C., about 400 at 500° C., about 360 at 600° C., and about 300 at 800° C.
Tables 6 to 8 show specific values of the Vickers hardness in
A rolling fatigue life test was carried out for the embodiment sample 1. Specifically, a thrust rolling fatigue life testing machine was used.
Firstly, the embodiment sample 1 was processed into a doughnut-shaped disk (outer diameter D of 60 mm×inner diameter d of 20 mm×thickness t of 6 mm) shown in
The test was carried out by using two types of axle bearings described below.
Table 9 shows the result of the rolling fatigue life test. Table 9 also shows the result of the rolling fatigue life test of the SUS630 (Fe-17-Cr-4Ni-4Cu-0.35Nb). The column of the “test result” indicates the rolling life of each material under each test condition.
It is found from Table 9 that the rolling life is almost equal to that of the SUS630 under the condition of the load of 250 kgf. The life time was 500 hours or more under the load of 43 kgf, which indicates that the embodiment sample 1 can sufficiently stand use at room temperature.
A heat-resistant rotation test was carried out for a ball bearing (embodiment) using an inner ring and an outer ring formed from the embodiment sample 1. Specifically, the ball bearing was rotated under high-temperature environment, and then, the appearance of the ball bearing was checked, and the size of the ball bearing was measured, whereby the ball bearing was evaluated. The same test was carried out for a ball bearing, which was assembled by an outer ring and an inner ring formed from SUS440C (Fe-18Cr-1C) and had the shape same as that formed from the embodiment sample. This ball bearing was also evaluated.
The condition of the test was as follows:
It is found from
Table 10 shows the result of the measurement of abrasion amount of the inner ring and the outer ring after the heat-resistant rotation test. It is found from Table 10 that the abrasion amount of the inner ring and the outer ring formed from the embodiment sample 1 is dramatically smaller than the abrasion amount of the inner ring and the outer ring formed from the SUS440C. It is understood from
The abrasion amount of the inner ring and the abrasion amount of the outer ring, formed from the material of the embodiment sample 1, due to the fatigue are considered to be the total abrasion amount of the axle bearing, and the life time of the axle bearing was calculated with the SUS440C being defined as a reference. With this calculation, it can be confirmed that the axle bearing whose inner ring and the outer ring were formed from the embodiment sample 1 took 8336 hours until the abrasion amount reached the amount equal to the abrasion amount of the axle bearing whose inner ring and the outer ring was formed from the SUS440C (Table 10). It is understood that the axle bearing formed from the embodiment sample 1 has extremely long life under high-temperature environment, and excellent heat resistance property.
As is understood from the results of the evaluation, the embodiment sample 1 is totally different from a general bearing material such as SUS440C in property, and the mechanical property of the embodiment sample 1 is hardly changed even with the temperature rise. The axle bearing formed from the embodiment sample 1 is equal to the SUS440C in the rolling fatigue life test at room temperature, but it has very long life and exhibits excellent heat resistance property in the heat-resistant rotation test under high-temperature environment. Accordingly, the axle bearing formed from the embodiment sample 1 is well adapted for the usage requiring long life at high temperature.
Since the Ni3(Si, Ti)-based intermetallic compound alloy has a non-magnetic property, the axle bearing formed from this intermetallic compound alloy is difficult to produce deposition of abrasion powders into the raceway ring, the deposition being caused by magnetization. Consequently, it has a property of suppressing acceleration of abrasion. This axle bearing is also well adapted to the usage (e.g., semiconductor manufacturing device) requiring non-magnetic property.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-175851 | Jul 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/062640 | 7/27/2010 | WO | 00 | 2/14/2012 |
