Titanium boride

Abstract

A titanium metal or a titanium alloy having submicron titanium boride substantially uniformly dispersed therein and a method of making same is disclosed. Ti power of Ti alloy powder has dispersed within the particles forming the powder titanum boride which is other than whisker-shaped or spherical substantially uniformly dispersed therein.

Description

BACKGROUND OF THE INVENTION

Relatively small boron additions to conventional titanium alloys provide important improvements in strength, stiffness and microstructural stability. Because boron is essentially insoluble in titanium at all temperatures of interest, the titanium boride is formed for even very small boron additions. The density of titanium boride is nearly equal to those of conventional Ti alloys, but its stiffness is over four times higher than conventional titanium alloys. Thus, titanium boride offers significant improvements in stiffness, tensile strength, creep, and fatigue properties. Since titanium boride is in thermodynamic equilibrium with titanium alloys, there are no interfacial reactions to degrade properties at elevated temperature. Further, because the coefficient of thermal expansion of titanium boride is nearly equal to values for titanium alloys, residual stresses are nearly eliminated” Taken from JOM Article May 2004 “Powder Metallurgy Ti-6Al-4V Alloys: Processing, Microstructure, and Properties”, the entire disclosure of which is incorporated by reference.

Currently two approaches appear to be used to accomplish boron addition; 1) Blended elemental addition of TiB₂ and solid state reaction to produce the titanium boride which usually forms as whiskers with a 10 to 1 aspect ratio and 2) Pre-alloyed powders from a melt process.

Negatives of the blended elemental approach are the added effort to blend the powders to obtain a uniform distribution (which is never perfect) and the added time and temperature it takes the solid state reaction to transform TiB₂ to TiB (1300 C for 6 hours). Also, this approach has the potential to form larger Titanium boride particles or have residual titanium boride particles that adversely affect properties. The titanium boride whiskers that are formed can lead to anisotropic properties of the part depending on the type of process used to make the part.

A negative of the pre-alloyed approach is that it has a tendency to leave large primary borides in the pre-alloyed materials that cause low fracture toughness.

Representative examples of patents related to producing metal alloys with titanium boride are the Davies et al. U.S. Pat. No. 6,099,664 issued to Davies et al. Aug. 8, 2000, in which titanium boride particles in the 1-10 micron size range are produced in a molten reaction zone. The Blenkinsop et al. U.S. Pat. No. 6,488,073 issued Dec. 3, 2002 teaches the addition of an alloy in which tantalum boride or tungsten boride particles are added to a molten alloy material to form a molten mixture which upon cooling has the boride distributed therein. Another method of making boride containing titanium alloys is disclosed in the Abkowitz U.S. Pat. No. 5,897,830 in which titanium boride powders are mixed with the powders of various constituents to form a consumable billet which is thereafter cast or melted to form the article of manufacture. Each of these processes as described in the above-mentioned patents has a variety of shortcomings, not the least of which is the imperfect distribution of the boride as well as the size of the boride particles.

SUMMARY OF THE INVENTION

The Armstrong Process as disclosed in U.S. Pat. Nos. 5,779,761, 5,958,106 and 6,409,797, the entire disclosures of which are herein incorporated by reference appears very unexpectedly to give uniform distribution of very fine submicron titanium boride within the Ti or Ti alloy powder. This eliminates the need for blending and solid state reaction to form titanium boride; it also eliminates concerns regarding larger particles that can adversely affect fracture toughness and other mechanical properties. Because of the fineness of the titanium boride particles and the uniform distribution in most if not substantially all of the particles forming the powder, more isotropic mechanical properties may be achievable. None of the current approaches to boron addition to Ti powder can achieve this type of distribution of titanium boride, particularly in the submicron size ranges.

Accordingly, it is a principal object of the present invention to provide a titanium metal or a titanium alloy having submicron titanium boride substantially uniformly dispersed therein.

Another object of the invention is to provide a Ti powder or a Ti base alloy powder having submicron titanium boride substantially uniformly dispersed therein, wherein the Ti powder or Ti base alloy powder and titanium boride are made by the subsurface reduction of TiCI₄ and a boron halide and other chlorides and/or halides of the Ti base alloy constituents, if present, with liquid alkali or alkaline earth metal or mixtures thereof in a reaction zone.

A further object of the invention is to provide a Ti powder or a Ti base alloy powder having submicron titanium boride which is other than whisker-shaped or spherical substantially uniformly dispersed therein.

A final object of the invention is to provide a product having an SEM substantially as shown in one or more of FIGS. 1-8.

The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated.

FIG. 1 is an SEM of a titanium powder having submicron titanium boride substantially uniformly dispersed therethrough at a magnification of 50;

FIG. 2 is another SEM of a titanium powder having submicron titanium boride substantially uniformly dispersed therethrough at a magnification of 50;

FIG. 3 is a similar SEM of a titanium powder having submicron titanium boride substantially uniformly dispersed therethrough at a magnification of 3000;

FIG. 4 is another SEM of a titanium powder having submicron titanium boride substantially uniformly dispersed therethrough at a magnification of 3000;

FIG. 5 is a titanium base alloy having about 10% total of aluminum and vanadium with titanium boride with submicron titanium borides substantially uniformly dispersed throughout the particles forming the powder at a 40 magnification;

FIG. 6 is a titanium base alloy having about 10% total of aluminum and vanadium with titanium boride with submicron titanium borides substantially uniformly dispersed throughout the particles forming the powder at a 50 magnification;

FIG. 7 is a titanium base alloy having about 10% total of aluminum and vanadium with titanium boride with submicron titanium borides substantially uniformly dispersed throughout the particles forming the powder at a 3000 magnification;

FIG. 8 is a titanium base alloy having about 10% total of aluminum and vanadium with titanium boride with submicron titanium borides substantially uniformly dispersed throughout the particles forming the powder at a 3000 magnification (a different portion of the same sample as FIG. 7).

DETAILED DESCRIPTION OF THE INVENTION

Using the Armstrong method described in the above three identified patents and application Ser. No. 11/186,724 filed Jul. 21, 2005, the entire application is herein incorporated by reference.

The equipment used to produce the 6/4 alloy with submicron titanium boride substantially uniformly dispersed therein is similar to that disclosed in the aforementioned patents disclosing the Armstrong Process with the exception that instead of only having a titanium tetrachloride boiler 22 as illustrated in those patents, there is also a boiler for each constituent of the alloy connected to the reaction chamber by suitable valves. Boron addition is from a boiler for BCl₃. The piping acts as a manifold so that the gases are completely mixed as they enter the reaction chamber and are introduced subsurface to the flowing liquid sodium, preferably at least at sonic velocity, as disclosed in the incorporated patents. Upon subsurface contact with the liquid metal the halides immediately and completely react exothermically to form a reaction zone in which the reaction products are produced. The flowing liquid metal preferably sodium, sweeps the reaction products away from the reaction zone maintaining the reaction products at a temperature below the sintering temperatures of the reaction products. It was determined during production of the 6/4 alloy that aluminum trichloride is corrosive and required special materials not required for handling either titanium tetrachloride or vanadium tetrachloride. Therefore, Hastelloy C-276 was used for the aluminum trichloride boiler and the piping to the reaction chamber. The BCl₃ is not as corrosive as AlCl₃.

During most of the runs the steady state temperature of the reactor was maintained at about 400° C. by the use of sufficient excess sodium. Other operating conditions for the production of the 6/4 alloy powder with submicron titanium boride dispersed in most, if not substantially all, of the particles forming the powder were as follows:

A device similar to that described in the incorporated Armstrong patents was used except that a VCl₄ boiler, a AlCl₃ boiler and a BCl₃ boiler were provided and all three gases were fed into the line feeding TiCl₄ into the liquid Na. The typical boiler pressures and system parameters are listed hereafter in Table 1.

TABLE 1
					TiCl4					Boron			Bake
					Noz.	TiCl4	TiCl4	VCl4	AlCl3	Noz.	Boron	Distill	Temp(C.)/
	Boron	Aluminum	Vanadium	Oxygen	Dia.	Press.	Flow	Press.	Press.	Dia.	Press.	Temp	Time
Run#	Wt %	Wt %	Wt %	Wt %	(in)	(Kpa)	(Kg/min)	(Kpa)	(Kpa)	(in)	(Kpa)	(C.)	(hrs)
NR285	.82	—	—	.485	7/32	540	2.4	—	—	.040	640	575	750/24
	.89			.477
	.9			.605
	.82			.578
NR286	2.21	—	—	.874	7/32	500	2.3	—	—	.040	1400-1600	575	775/24
	3.17			.875
	3.15			.985
	3.18			.969
NR291	.25	7.08	2.84	.346	7/32	500	2.9	640	860	.040	600	575	775/24
	.38	6.91	2.5	.494
NR292	2.58	7.46	3.79	1.06	7/32	510	2.2	620	850	.040	1500	575	775/24
	2.49	7.72	3.59	1.33
A-308	.71	—	—	.304	7/32	500	2.5	—	—	.040	450-525	575	790/30
	.64			.303
A-328	1.24	—	—	.31	5/32	550	1.23	—	—	.040	570	575	790/36
Inlet Na temperature about 240° C.
Reactor Outlet Temperature about 510° C.
Na Flowrate about 40 kg/min

The reactor was generally operated for approximately 250 seconds injecting approximately 11 kg of TiCl₄. The salt and titanium alloy solids were captured on a wedge wire filter and free sodium metal was drained away. The product cake containing titanium alloy, sodium chloride and sodium was distilled at approximately 100 milli-torr at 550 to 575° C. vessel wall temperatures for 20 hours. Once all the sodium metal was removed via distillation, the trap was re-pressurized with argon gas and heated to 750° C. and held at temperature for 48 hours. The vessel containing the salt and titanium alloy cake was cooled and the cake was passivated with a 0.7 wt % oxygen/argon mixture. After passivation, the cake was washed with deionized water and subsequently dried in a vacuum oven at less than 100° C.

Table 2 below sets forth a chemical analysis of various runs for both Ti as well as 6/4 alloy with submicron titanium boride substantially uniformly dispersed therein from an experimental loop running the Armstrong Process. As used herein, titanium boride means principally TiB but does not exclude minor amounts of TiB₂ or other borides.

Similarly, the process described herein produces a novel powder in which most, if not substantially all, of the particles forming the powder have submicron titanium boride dispersed therein. While the boride dispersion may not always be perfect in every particle, the titanium boride is very small, submicron, and generally uniformly dispersed within the particles forming the powder, whether the powder is titanium or a titanium alloy.

As seen from Table 2 below, the sodium levels for 6/4 with submicron titanium boride are very low while the sodium level for Ti with submicron titanium boride are somewhat higher, but still less than commercially pure titanium, without submicron titanium boride dispersed therein, made by the Armstrong Process, as described in the incorporated application.

As stated in the referenced application, the surface area of the 6/4 alloy compared to the CP titanium, as determined using BET Specific Surface Area analysis with krypton as the adsorbate is much larger than the CP titanium. The surface area of the 6/4 alloy with titanium boride is even greater, that is the alloy powder with titanium boride was smaller in average diameter and more difficult to grow into larger particles than Ti alloy without titanium boride.

	TABLE 2
	Al % by weight	V % by weight	B % by weight	Na
	9	5		0.0039
	10	5		0.0026
	8	5		0.001
	7	2.2		0.017
	8	1.8		0.0086
	5.4	5.3		0.0015
	7.3	4.7		0.002
	14	3		0.018
	7.75	5.2		0.009
	9.6	6.8		0.0078
	13	6.7		0.0092
	9.2	0.009		0.014
	6	4		0.0018
	5.7	3.5		0.0018
	5	2.2		0.0018
	5.3	3.6		0.0052
	7.2	4		0.014
			0.82	0.018
			0.89	0.023
			0.9	0.0047
			0.82	0.0028
			2.21	0.0047
			3.17	0.0076
			3.15	0.013
			3.2	0.012
	7.08	2.84	0.25	0.0025
	6.91	2.5	0.38	0.0024
	7.46	3.79	2.58	0.0023
	7.72	3.59	2.49	0.0077

The SEMs of FIGS. 1-8 show that the 6/4 powder and/or Ti powder with submicron titanium boride distributed therein is “frillier” than the previously made 6/4 powder in the referenced application. Each of the figures references a run disclosed in Table 1 and represents samples taken from that run at different magnifications. As stated in the referenced application and as reported by Moxson et al., Innovations in Titanium Powder Processing in the Journal of Metallurgy May 2000, it is clear that by-product fines from the Kroll or Hunter Processes contain large amounts of undesirable chlorine which is not present in the CP titanium powder or alloy made by the Armstrong Process. Moreover, the morphology of the Hunter and Kroll fines, as previously discussed, is different from the CP powder or the 6/4 alloy powder or either with submicron titanium boride therein made by the Armstrong Process. Neither the Kroll nor the Hunter process has been adapted to produce 6/4 alloy or any alloy. Alloy powders have been produced by melting prealloyed stock and thereafter using either gas atomization or a hydride-dehydride process (MHR). The Moxson et al. article discloses 6/4 powder made in Tula, Russia and as seen from FIG. 2 in that article, particularly FIGS. 2c and 2d the powders made by Tula Hydride Reduction process are significantly different than those made by the Armstrong Process. Moreover, referring to the Moxson et al. article in the 1998 issue of the International Journal of Powder Metallurgy, Vol. 4, No. 5, pages 45-47, it is seen that the chemical analysis for the pre-alloy 6/4 powder produced by the metal-hydride reduction (MHD) process contains exceptional amounts of calcium and also is not within ASTM specifications for aluminum.

As is well known in the art, solid objects can be made by forming 6/4 or CP titanium powders into a near net shapes and thereafter sintering, see the Moxson et al. article and can also be formed by hot isostatic pressing, laser deposition, metal injecting molding, direct powder rolling or various other well known techniques. Therefore, the titanium alloy powder or titanium powder with submicron titanium boride dispersed substantially uniformly therein made by the Armstrong method may be formed into a consolidated or a consolidated and sintered product or may be formed into a solid object by well known methods in the art and the subject invention is intended to cover all such products made from the powder of the subject invention.

There has been disclosed herein a titanium metal powder or a titanium base alloy powder having submicron titanium boride substantially uniformly dispersed therein.

The specific titanium alloy of the type set forth wherein Al and V are present in a minor amount by weight, but preferably ASTM Grade 5, as well as commercially pure titanium, ASTM Grade 2, both as disclosed in the incorporated patent application, Table 1 therein, with submicron titanium boride substantially uniformly dispersed therein have been disclosed, wherein boron is present up to about 4% by weight. The invention however, includes any weight of boron added. Preferably, alloys have at least 50% by weight titanium with titanium boride, preferably TiB, present in any required amount.

Any halide may be used in the process, as previously described, but chlorides are preferred because they are readily available and less expensive than other halides. Various alkali or alkaline earth metals may be used, i.e. Na, K, Mg, Ca, but Na is preferred.

Solid products are routinely made by a variety of processes from the powders described herein. Products made from powder produced by the Armstrong method including BCl₃ introduced into flowing liquid reducing metal prod uce superior hardness and other desirable physical properties are within the scope of this invention.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that several changes in form and detail may be made without departing from the spirit and scope of the invention.

Claims

1. A method of forming a titanium metal powder, the method comprising: subsurfacely introducing a vapor mixture of titanium tetrachloride and a boron halide into a flowing stream of a liquid metal comprising an alkali metal, an alkaline earth metal, or a mixture thereof, to produce the reaction products comprising titanium metal powder having submicron titanium boride substantially uniformly dispersed therein, wherein the liquid metal is present in a sufficient amount to (i) reduce the vapor mixture to form the reaction products, and (ii) maintain the reaction products below a sintering temperature of the titanium metal powder; andrecovering the titanium metal powder from the reaction products.

2. The method of claim 1 wherein the titanium metal powder comprises boron in an amount greater than 0% by weight up to 3.2% by weight of the titanium metal powder.

3. The method of claim 1 wherein the titanium metal powder comprises boron in an amount greater than 0% by weight up to about 4% by weight of the titanium metal powder.

4. The method of claim 1, wherein the titanium boride is other than whisker-shaped or spherical shaped.

5. The method of claim 1, further comprising forming the titanium metal powder into a consolidated powder.

6. The method of claim 1, further comprising sintering the titanium metal powder to form a sintered powder.

7. The method of claim 1, wherein the titanium boride is principally in the form of TiB.

8. The method of claim 1, wherein the alkali metal is at least one of sodium and potassium.

9. The method of claim 1, wherein the alkaline earth metal is at least one of magnesium or calcium.

10. The method of claim 1, wherein the vapor mixture is introduced into the flowing stream of liquid metal at at least sonic velocity.

11. The method of claim 1, wherein the boron halide substantially comprises BCl3.

12. The method of claim 1, wherein at least half of the particles forming the titanium metal powder contain titanium boride.

13. The method of claim 1, wherein the titanium boride is dispersed within substantially all of the particles of the titanium metal powder.

14. The method of claim 1, further comprising subsurfacely introducing at least one of Al and V to form a titanium alloy of at least one of Al and V.

15. The method of claim 1, comprising the step of consolidating the titanium metal powder into a solid object.

16. A method of forming a titanium metal powder, the method comprising: subsurfacely introducing a vapor mixture of titanium tetrachloride and a boron halide into a flowing stream of a liquid metal comprising an alkali metal, an alkaline earth metal, or a mixture thereof, to produce the reaction products comprising titanium metal powder having submicron titanium boride substantially uniformly dispersed therein, wherein the titanium metal powder comprises boron in an amount greater than 0% by weight up to about 4% by weight of the titanium metal powder, and wherein the liquid metal is present in a sufficient amount to (i) reduce the vapor mixture to form the reaction products, and (ii) maintain the reaction products below a sintering temperature of the titanium metal powder; andrecovering the titanium metal powder from the reaction products.

17. The method of claim 16 wherein the titanium metal powder comprises boron in an amount greater than 0% by weight up to 3.2% by weight of the titanium metal powder.

18. The method of claim 16, wherein the titanium boride is other than whisker-shaped or spherical shaped.

19. The method of claim 16, wherein the titanium boride is principally in the form of TiB.

20. The method of claim 16, wherein the boron halide substantially comprises BCl3.

21. The method of claim 16, further comprising subsurfacely introducing at least one of Al and V to form a titanium alloy of at least one of Al and V.