Patent Application
20090041609
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The present invention relates to sintered titanium metal matrix composites discontinuously-reinforced with dispersed ceramic and intermetallic particles such as silicon carbide, titanium borides, vanadium carbides, titanium aluminides, etc.
Titanium-based or titanium alloy-based metal matrix composites (TMMC) are of particularly great interest in the following areas: the aerospace and automotive industries, medical implants, armor, and chemical-resistant applications due to their high specific strength, high stiffness, low weight, and relatively high wear resistance. The titanium or titanium alloy matrix in these composites are reinforced by fibers or particles which have a substantially higher hardness and elastic modulus than the matrix alloy. Reinforcing components should be thoroughly and uniformly dispersed in the volume of the matrix alloy to achieve the maximum mechanical properties of the composite material. In addition, the optimum combination of the mechanical properties of the composite material depends upon the sizes of the reinforcing particles, strength of the bond between the hard particles and the matrix alloy, and the porosity of sintered composite materials.
Despite more than twenty years of experience in industrial applications, conventional TMMC are far from perfection and being used only on a limited scale. The limitation of their usage is mostly associated with non optimized combination of mechanical properties associated with remaining porosity, not uniform chemistry and distribution of hard particles as well as absence of well developed and optimized manufacturing processes.
For example, the method for manufacturing the Ti-6Al-4V/TiC composite disclosed in the U.S. Pat. No. 5,722,037 provides the density of the resulting material only about 93% of the theoretical value even after vacuum sintering for 4 hours at 1300° C. The method includes formation of reinforcing TiC particles in the titanium matrix by chemical reaction with hydrocarbon gas that is more effective in the porous matrix than in the dense one.
In the U.S. Pat. No. 4,731,115 granted to Abkowitz, et al., a TiC/titanium alloy composite cladding material and process for manufacturing the same are disclosed, in which blended components are compacted by cold isostatic pressing and sintered at 2200-2250° F. However, this method does not provide sufficient density of the material, and to improve the density, the invention further includes encasing the sintered pre-form and hot isostatic pressing (HIP) at 1650-2600° F. followed by finish forging, rolling, or extruding. This method is not so cost-effective due to the additional HIP step and requires encasing that should be further removed from the final product by grinding or chemical milling. Moreover, the HIP process does not permit production of articles with close tolerances of their sizes. Requirements for encapsulating are probably associated with the interconnected porosity which prevents full consolidation and extensive surface oxidation taking place during HIP process.
T. Kaba, et al. (U.S. Pat. No. 5,534,353) proposed compacting a powdered component blend by cold isostatic pressing, atomizing the product by melting and spraying, and finally, sintering the atomized powder by HIP at 1100° C. (2012° F.). The final product has improved bending strength at room temperature, but includes atomizing in a protective atmosphere, and it still has an interconnected porosity which requires additional encapsulating step for the HIP process which increases cost of manufacturing the high temperature consolidated components.
A method for manufacturing titanium matrix composites, according to the U.S. Pat. No. 5,458,705, is mainly based on the precipitations of reinforcing particles from the titanium alloy matrix during the solidification and cooling of the matrix alloy. This means, that this method should include melting and casting of titanium alloys at the temperature above 1600° C. (2900° F.) that limits the applications of the resulting TMMC. Any additions of actual ceramic or intermetallic hard particles degrade flow rate during casting of molten composite alloy, creates segregation during casting process and, as a result, the reinforcing particles are not uniformly distributed in a resulting TMMS alloy, restricts is not uniform and makes the process not applicable, when the designs of the cast TMMK structures require to have the thin cross sections.
All previous processes for manufacturing the dense titanium matrix composites consisting of matrix alloy and reinforcing particles by using powder metallurgy approaches have considerable drawbacks associated with porosity and non-uniformity of reinforcing particles distribution which degrade ductility and strength of the TMMC and restrict applications of these manufacturing processes. These powder metallurgy processes also require the expensive high temperature consolidation in capsules to prevent oxidation due to extensive porosity which escalate cost of the manufacturing processes and limit an ability to control the sizes of finished components.
A significant difference in structural and mechanical properties between sintered material and the capsule produced from non-reactive wrought metal results in non-uniform deformation and stress concentration in the TMMC during hot deformation. Cracks in various areas of the sintered material observed during the first cycles of hot deformation are caused by interconnected porosity and stress concentration. These cracks restrict maintaining a reliable and reproducible manufacturing process through subsequent forging, hot rolling, or other high temperature deformation.
Some of the known casting processes to produce TMMC exhibited limitation in manufacturing the components with thin cross sections.
Therefore, it would be desirable to provide (a) a high-strength and fully-dense titanium matrix composites having near full density or insignificant closed porosity after sintering or other high temperature processing of green components, and (b) a cost-effective method for producing such composites using blended elemental powders or combination of pre-alloyed and elemental metal powder blends, as well. A new composition and manufacturing method would improve the application performance of resulting materials, as well as eliminate destructive effect of opened porosity and oxidation taking place during subsequent high-temperature processing or eliminate a need for expensive encapsulation operation which is required in order to achieve a near full density TMMC alloy with acceptable mechanical properties.
This present invention achieves this goal by using the complex carbides and borides as additional reinforcing components in the Ti/TiC, Ti/TiB2, and Ti/(TiC, TiB2) composite structures, and by providing a method through which the sintered structure has only the closed porosity at the near full theoretical density, while at the same time, the composite material exhibits acceptable mechanical properties in the as-sintered conditions, and/or if the complex shaped parts are being manufactured by subsequent high temperature deformation,—no encasing, canning, or encapsulating are required.
It is therefore, an object of the invention is to produce a fully-dense, essentially uniform structure of flat and shaped titanium metal matrix composite consisting of high-strength and ductile matrix with uniformly distributed re-enforcing particles providing improved mechanical characteristics such as toughness, flexure strength, impact strength, elastic modulus, and wear resistance.
Another object of this invention is to avoid interconnected porosity and manufacture the sintered composite material which may have only closed porosity and near full density after sintering, e.g., over 98% of the theoretical value.
Yet, another object of this invention is to produce near-full density parts from a titanium matrix composite material that has acceptable mechanical properties without a need for further hot deformation.
It is yet another object of this present invention is to provide a powder metallurgy technique for manufacturing near-net shape sintered TMMC that can be used as final product in the as-sintered state or in the state after hot deformation without secondary operations such as machining, chemical milling, or others.
It is yet another additional object of the invention is to establish a continuous cost-effective process to produce fully-dense flat and shaped titanium alloy matrix composite parts with controlled size tolerances from either blended elemental powders or from a combination of the pre-alloyed and elemental powders blend.
The nature, utility, and features of this invention will be more apparent from the following detailed description with respect to preferred embodiments of the invented technology.
While the use of a number of manufacturing processes including sintering and hot deformation has previously been contemplated in the titanium matrix composite industry, as mentioned above, the processing limitations related to an ability to manufacture a near full density composite structure by low cost room-temperature consolidation, limited process stability, inability to manufacture the components with controlled sizes when components with close tolerances are being produced, high production costs, defective microstructure, residual porosity, and insufficient mechanical properties of not fully dense TMMC articles, established a need for development of the new low cost manufacturing processes for producing the TMMC with optimized mechanical properties and improved performance. This invention overcomes shortcomings in the prior art.
The goals of the invention are (a) to change the type of porosity of the sintered semi-product from the interconnecting porosity to only discontinuous porosity at near full density, e.g., over 98% of the theoretical value after sintering, and (b) to improve mechanical properties at reduced cost of production process for manufacturing fully-dense titanium matrix composites.
An attempt was made to produce discontinuously reinforced TMMC using a blended elemental powder metallurgy approach. A newly developed process allows uniform distribution of reinforcing particles in the ductile matrix while improving the bond strength between the reinforcing particulate and the matrix alloy.
One novelty of the invention is the use of soluble complex borides and carbides (such as AlV2C, AlTi2Si3, AlTi6Si3, AlTi4Si7, Al3B48Si, VB2, V3B2, V3B4, TiVSi2, TiVB4, Ti2AlC, Ti3AlC, AlCr2C, TiAlV2, (Ti,V)C, (Ti,V)(B,C), V2C, V4C3, VSi2, Ta3B4, Ta3B2, Ti2Al(B,C), TaTiB4, NbTiB4, and/or Al3U2C3) for the reinforcement of titanium alloy matrixes along with elemental carbide and boride particles such as SiC, TiB, TiB2, Ti3B4, Ti2B5, B4C, ZrC, ZrB2, TaC, TaB, TaB2, Ta3B2, VB, V2B, WC, NbC, NbB, Nb3B2, Nb3B4, Al4C3, Al4C3, AlB2, TiAl, Ti3Al, TiAl3, Al8V5, VC, Cr7C3, HfC, UC, U2C3, and/or TiCr2. Said complex borides and carbides not only reinforce effectively the matrix titanium alloy, but also prevent its grain growth during the sintering and subsequent heat treatment.
Another novelty of this invention is consolidation of the blend of matrix and reinforcing powders at room temperature, whereby the reinforcing particles are not finally formed. The incompletely formed intermetallic particles are not as brittle as finally-formed intermetallics that results in effective consolidation to high degree of green body density, and besides, in reducing number of defects in the final product. The composite reinforcing particles are finally formed during the hot stage of the manufacture: sintering, forging, hot rolling, HIP, etc. These dispersed particles are grown from the solid solution, and therefore, they are completely compatible with the matrix microstructure. The resulting microstructure provides significant gain in strength of produced composite material.
There are two innovative approaches are being used in this invention to produce the particulates for reinforcement. First approach is preparing the reinforcing powders by co-attrition or mechanical alloying the reinforcing elemental powders and second approach is dealing with pre-sintering/backing and grinding the reinforcing elemental powders. Both approaches allow application of low cost room temperature consolidation of the particulates for reinforcement after they are blended either with pure titanium powder or with titanium powder mixed with master alloys, followed by sintering operation resulting in near full density TMMC structures. Actual formation of these TMMC structures is being created during high temperature processing of green pre-forms, i.e. in-situ formation of reinforced particulates uniformly distributed in titanium or titanium alloy matrix alloy.
The preparation of pre-sintered cakes is being performed at the temperatures which result in partial formation of the particulate reinforcement, and the reinforcement is created during the subsequent high temperature processing such as sintering and/or high temperature deformation (forging, hot pressing or rolling). These pre-sintered cakes do not have not finally formed reinforcing particles in the matrix alloy.
These cakes are made from boron and/or carbon powders reacted with aluminum or aluminum-vanadium master alloy at 800-1100° C., boron carbide and boron silicide powders reacted with titanium powder at 1200-1400° C., and titanium boride and/or silicon carbide powders are preliminary reacted with aluminum or aluminum-vanadium master alloy at 900-1100° C. We discovered that reaction products such as TiB2, Ti3SiC2, and other complex borides, carbides and silicides have better compatibility with the crystal lattice of matrix titanium alloys that results in additional strength and toughness of the composite materials. The formation of such reinforcing particles as TiB2, Ti3SiC2, and other complex borides, carbides and silicides occurs during hot treatment and cooling of the previously green body. Therefore, the complete size and particle distribution are formed only in final products.
The co-attrition or mechanical alloying of the Al—V master alloy powder with hard reinforcing particles of above-mentioned ceramics and intermetallics is among other novelties of this invention.
A combination of unique properties of (i) high strength and stiffness at temperatures up to 820° C. (1500° F.), (ii) good mechanical properties at room temperature including good ductility, (iii) improved resistance to matrix cracking, and (iiii) very close controlled tolerances of sizes of the finished parts which is achieved in the resulting material by forming a discontinuous porosity of sintered semi-product followed by effective densification during subsequent high temperature deformation. Also, as sintered, near full density product may be high temperature deformed (HIPped, forged, or rolled) without a need for encapsulation.
The invented compositions and methods are suitable for the manufacture of flat or shaped titanium matrix composite articles having improved mechanical properties such as lightweight plates and sheets for aircraft and automotive applications, armor plates, heat-sinking lightweight electronic substrates, bulletproof structures for vests, partition walls and doors, as well as sporting goods such as helmets, golf clubs, sole plates, crown plates, etc.
The subsequent objects, features, and advantages of our invented material and process will be clarified by the following detailed description of the preferred embodiments of the invention.
As discussed, the present invention relates generally to the manufacture of titanium matrix composites that are reinforced by ceramic and/or intermetallic particles using a combination of elemental and pre-alloyed powders (obtained by atomization or other method), elemental metal powder blends, and/or titanium hydrides, or a combinations thereof (i.e. combination of pre-alloyed, elemental and/or hydrogenated powders as raw materials).
Use of preliminary prepared fine powder of Aluminum-Vanadium master alloy plays a unique role in this process and results in formation of highly-dense structure developed during sintering and manufacturing a semi-finished product or finished product having solely closed discontinuous porosity at density over 98% of the theoretical value. The co-attrition or mechanical alloying of the master alloy powder with hard reinforcing, ceramic and intermetallic particles plays important role in the formation of fine microstructure of the resulting composite material with good bonds between the matrix and reinforcing particles developed during subsequent sintering of room temperature consolidated (die pressed, or cold isostatic pressed or direct powder rolled) green pre-forms. No previously known methods, mentioned in References, allow producing such composite structure because they used finally structured, brittle reinforcing particles in the starting blend. This results in crushing those brittle particles during both room temperature consolidation and high-temperature processing (such as forging, rolling, and hot pressing) creating multiple defects in the composite material structure such as cracks, voids, and stress concentrators.
The addition of complex carbide- and/or silicide particles that are at least partially soluble in the matrix such as AlV2C, AlTi2Si3, AlTi6Si3, AlTi4Si7, Al3B48Si, VB2, V3B2, V3B4, TiVSi2, TiVB4, Ti2AlC, Ti3AlC, AlCr2C, TiAlV2, (Ti,V)C, (Ti,V)(B,C), V2C, V4C3, VSi2, Ta3B4, Ta3B2, Ti2Al(B,C), TaTiB4, NbTiB4, and/or Al3U2C3 dispersed in the matrix in the amount of ≦50 vol. % allows not only control ductility of the matrix during any hot deformation of the sintered pre-form, but also significantly improves the effect of particle reinforcement of the resulting composite material. The above mentioned dispersed particles are formed “in-situ” after final stages of the composite manufacture: hot treatment and cooling. In order to reach the effect of full compatibility of reinforcing particles with matrix alloy, the process includes following steps:
Complex carbides combine merits of both metals and ceramics. Like metals, they are resistant to thermal shock, but like ceramics, they have high strength, hardness, and thermal stability. Such complex carbides as AlTi2Si3, AlTi6Si3, TiVSi2, TiVB4, Ti2AlC, Ti3AlC, AlCr2C, TiAlV2 have unique compressive plasticity at room temperature and high temperature that allows plastic deformation of the reinforced matrix without cracking. When the sintered composite material pre-form is heated to 1500-1700° F. for forging or hot rolling, the complex carbides are partially dissolved in the matrix, and the matrix alloy being freed of the carbide reinforcements is easily deformed at these temperatures. We can use pre-sintering, so that the alloys may be easily subjected to high temperature deformation, but in the most cases we want to produce TMMC without any high temperature deformation, i.e. final carbides and other reinforcing particulates to be formed in-situ during sintering. Complex boride and carbide powders are manufactured separately for adding into the basic powder blend. Some of these phases can be precipitated during cooling after hot deformation and fix fine grain structure of forged or hot rolled composite material.
A novel method for preparation of reinforced composite structure was used in this invention. The composite components (especially reinforcing ceramic or intermetallic particles are prepared by grounding the preliminary reacted pre-sintered cakes. These cakes are made:
(a) from boron and/or carbon powders reacted with aluminum or aluminum-vanadium master alloy at 800-1100° C.,
(b) boron carbide and boron silicide powders reacted with titanium powder at 1200-1400° C., and
(c) titanium boride and/or silicon carbide powders reacted with aluminum or aluminum-vanadium master alloy at 900-1100° C.
These pre-sintered cakes are ground for dispersed particles which are subsequently mixed with the basic elemental powder blend. We discovered that reaction products such as TiB2, TiC, Ti3SiC2, and other complex borides, carbides and silicides have better compatibility with the crystal lattice of matrix titanium alloys that results in additional strength and toughness of the composite materials.
We found that boron carbide B4C powder reacts with titanium powder at 1200-1400° C. with the formation of both titanium boride phases TiB2, TiB, and titanium carbide TiC. If titanium powder is taken in the excessive amount, these reaction products are synthesized immediately in the contact with titanium particles that improve the bond between reinforcing borides and carbides with the main component of the matrix alloy.
Similar reaction occurs between silicon carbide SiC and titanium with the formation of very effective reinforcing particles of Ti3SiC2.
The co-attrition or mechanical alloying of the Al—V master alloy powder with hard reinforcing particles of above-mentioned ceramics and intermetallics is among other novelties of this invention.
The foregoing examples of the invention are illustrative and explanatory. The examples are not intended to be exhaustive and serve only to show the possibilities of the invented technology.
A TiB2— and SiC-reinforced titanium composite material based on the Ti-6Al-4V alloy matrix was manufactured by (a) preparing a basic powder blend containing titanium powder and having a particle size ≦200 mesh (≦74 microns) for 95% of the powder, 5% of graphite, 2.5% of dispersing SiC powder, 7.5% of dispersing TiB2 particles, and 2.5% of dispersing powders of AlTi2Si3, (Ti,V)(B,C), and TiVB4 complex intermetallic particles partially soluble in the matrix at 1500-2300° F., (b) making a powder of Al—V master alloy having a particle size of 10 μm and less, (c) co-attrition of 30% of this master alloy powder with reinforcing powders, (d) mixing the basic powder blend with the master alloy powder and reinforcing particles at the weight ratio between titanium powder and master alloy of 9:1 to obtain a chemical composition of titanium matrix composite material, (e) compacting the powder mixture at room temperature by cold isostatic pressing, (f) sintering at 2300° F., (g) forging at 1600° F., and (h) cooling.
Sintered semi-product had density 98.9% with closed discontinuous porosity that allowed to perform the forging operation in air without encapsulating the sintered preform. The resulting (TiB2—SiC)/Ti-6Al-4V composite material has 100% density, and exhibits improved yield strength at room temperature and at 930° F. (500° C.).
A carbide-reinforced titanium composite material based on the Ti-6Al-4V alloy matrix was manufactured by (a) preparing a basic powder blend containing titanium powder having a particle size ≦140 mesh (≦100 μm) for 95% of the powder, 2% of graphite, 15% of dispersing SiC powder, and 4% of dispersing AlV2C, Ti2AlC, and V2C particles partially soluble in the matrix at 1500-2300° F., (b) making a powder of Al—V master alloy having a particle size of 10 μm and less, (c) mixing the basic powder blend with the master alloy powder, in the ratio of 9:1 to obtain a chemical composition of titanium matrix composite material, (d) compacting the powder mixture at room temperature by die-pressing, (e) sintering at 2350° F., (f) forging at 1600° F., and (g) cooling.
Sintered semi-product had a density of 99% with closed discontinuous porosity that allowed it to carry out forging in open air without encapsulating (or encasing). The resulting carbide-reinforced Ti-6Al-4V matrix composite material has 100% density, and it exhibits improved yield strength at room temperature and at 930° F. (500° C.), and satisfied oxidation resistance up to 1470° F. (800° C.).
The titanium matrix composite was manufactured using the same raw materials for Ti-6Al-4V matrix alloy and carbide reinforcements, and the same mode of sintering as in Example 1. The final hot deformation was made by hot rolling at 1650° F. instead of forging.
The resulting TiC/Ti-6Al-4V composite material also had 100% density, and exhibited satisfied yield strength at room temperature and at 930° F. (500° C.).
The boride-reinforced titanium composite material based on the Ti-6Al-4V alloy matrix was manufactured by (a) preparing a basic powder blend containing titanium powder having a particle size ≦200 mesh (≦74 microns) for 95% of the powder, 5% of graphite, 12.5% of the dispersing TiB2 powder, and 2.5% of the dispersing VB2, TiVB4, and NbTiB4, complex boride particles partially soluble in the matrix at 1500-2300° F., (b) the TiB2 powder was prepared by reacting B4C powder with titanium powder at 2280° F. (1250° C.) followed by grinding the pre-sintered cake, (c) making a powder of Al—V master alloy having a particle size of 10 Mm and less, (d) mixing the basic powder blend with the master alloy powder at the ratio of 9:1 to obtain a chemical composition of titanium matrix composite material, (e) compacting the powder mixture at room temperature by cold isostatic pressing, (f) sintering at 2450° F., and (g) cooling.
The resulting composite material has density 99.3% of the theoretical value with closed discontinuous porosity and exhibits acceptable yield strength at room temperature and at 930° F. (500° C.). The cost-effective plate of this material was used as final product without hot deformation.
