WO2010036131A1

WO2010036131A1 - Production of titanium alloys in particulate form via solid state reduction process

Info

Publication number: WO2010036131A1
Application number: PCT/NZ2009/000202
Authority: WO
Inventors: Jing Liang
Original assignee: Titanox Development Limited
Priority date: 2008-09-25
Filing date: 2009-09-25
Publication date: 2010-04-01

Abstract

The invention relates to a method for the production of titanium alloy particulate materials, in particular the invention relates to a process for producing titanium metal alloys via a Solid State Reduction (SSR) process from Titanium oxide (TiO₂) and alloying metal oxides and / or elemental metals. A variety of particulate titanium alloys, such as Ti-6Al-4V, Ti-55Ni,γ -Ti-48Al, α₂-Ti₃Al, Ti-28Nb, Ti-24Nb-3Al, can be produced by mixing metal oxides and / or elemental metals with calcium hydride (CaH₂) and heating to carry out a solid state reduction.

Description

PRODUCTION OF TITANIUM ALLOYS IN PARTICULATE FORM VIA SOLID STATE REDUCTION PROCESS

Technical Field

The invention relates to a method for the production of metal alloy powders, in particular the invention relates to a method for the production of titanium alloy powders from titanium oxide starting materials.

Background Art

Titanium alloys have many advantages over other non-ferrous and ferrous metallic materials, such as the highest strength-to-weight ratio of all materials up to 550⁰C and excellent corrosion resistance. Despite titanium being the fourth most abundant metal in the earth's crust (0.86% by weight) behind aluminium, iron and magnesium, titanium alloys are not particularly widely used, primarily due to the cost of extraction, processing and fabrication.

Powder metallurgy (P/M) offers the advantage of manufacturing near net shaped products with a considerable increase in the materials utilization factor in the case of titanium alloys. Innovative P/M techniques, such as laser sintering and metal injection moulding, provide near waste free processes to fabricate near net shape components. The metal powders that are desirable for use in these techniques require fine particle size with good fluidity.

There are a number of processes for the production of metal and metal alloy powders that have been described in the patent literature including, for example, that described in WO2004009857 entitled "A Separation Process" also to Titanox Development Limited. This document teaches the manufacture of metal alloy powders (e.g. TiAI) via a coarsening (increase particle size) and separation step. This can then be followed by further reduction step using, amongst other reducing agents, calcium hydride. The present invention relates to a new processing route for the production of a variety of titanium alloys in fine particulate form. The process comprises the homogenization annealing of titanium oxide (TiO₂), followed by the crushing and screening for particle size of the resulting TiO₂. The screened TiO₂ particles of titanium oxide are then mixed with alloying metal oxides and/or elemental metals and calcium hydride (CaH₂). On heating at a temperature below the melting point of the alloy, the titanium oxide and alloying metal oxides and/or elemental metals are reduced and alloyed homogeneously. The titanium alloy powders are recovered.

Object Of the Invention

There would be an advantage in being able to provide alternative methods for producing high quality titanium alloy powder material in a cost-effective manner or at least provide the public with a useful choice.

Summary of the Invention

In a first aspect, the invention provides a process for the manufacture of multi-compound titanium alloy powder, the method including the following steps:

(a) homogenization annealing of TiO₂,

(b) crushing and screening the results of (a) to the required particle size,

(c) mixing the result of (b) with alloying metal oxide and/or elemental metal powders and CaH₂ and heating at a temperature below the melting point of the alloy, (d) recovering the alloy powder.

Preferably the homogenization annealing in step (a) is carried out at about 1200⁰C to about 1400⁰C. Preferably the homogenization annealing in step (a) is carried out for about 2 to about 5 hours.

Preferably the homogenization annealing in step (a) is carried out in an inert environment.

Preferably the inert environment is an argon or vacuum environment.

Preferably the required particle size in step (b) is selected to give a desired particle size of alloy powder.

Preferably the crushing is carried out using a ball or discus milling machine.

Preferably the screening is carried out using mechanical sieves.

Preferably the alloying metal oxide is selected from any one or more of: V₂O₅, NiO, AI₂O₃, Nb₂O₅, Ta₂O₅, Fe₂O₃, ZrO₂, MoO₂ and Cr₂O₃.

Preferably the elemental metal is selected from any one or more of: Al and Sn.

Preferably the temperature below the melting point of the alloy in step (c) is greater than about 110O⁰C.

Preferably the temperature below the melting point of the alloy in step (c) is between about 110O⁰C and about 1400⁰C.

Preferably the temperature below the melting point of the alloy in step (c) is between about 1200⁰C and about 1300⁰C.

Preferably the components in step (c) are heated at a temperature below the melting point of the alloy for at least about two hours.

Preferably the components in step (c) are heated at a temperature below the melting point of the alloy for about 2 to about 6 hours.

Preferably the components in step (c) are heated at a temperature below the melting point of the alloy in an inert environment.

Preferably the inert environment is an argon or vacuum environment.

Preferably the result of step (c) is washed.

Preferably the result of step (c) is washed with weak acidic solution and/or deionised water.

Preferably the alloy powder recovered is selected from an alloy of Ti with any one or more of V, Ni, Al, Nb, Zr, Ta, Fe, Zr, Mo and Cr.

Preferably the alloy powder recovered is selected from any one or more of: Ti-Al-V, Ti-Ni, Ti-Al, Ti-Nb, Ti-Nb-Al, Ti-Nb-Zr-Ta, Ti-V-Fe-Al, Ti-Al-Sn-Zr-Mo alloys.

In a second aspect the invention provides a process for the manufacture of multi-compound titanium alloy powder, the method including the following steps: (a) homogenization annealing of TiO₂ at about 1200⁰C to about 1400⁰C, for about 2 to about 5 hours, in an inert environment of argon, (b) crushing and screening the results of (a) to the required particle size, wherein the required particle size is selected to give a desired particle size of alloy powder, (c) mixing the result of (b) with alloying metal oxide and/or elemental metal powders and CaH₂ and heating at a temperature of between about 1200⁰C and about 1300°C for about 2 to about 6 hours, (d) washing the result of step (c) with weak acidic solution and/or deionised water,

(e) recovering the alloy powder.

In a third aspect the invention provides an alloy powder produced by the process described in the first or second aspect.

Brief Description of Drawings

Figure 1 shows a SEM image of T1-6AI-4V particles with diameter around 10 μm. Figure 2 shows an EDX analysis of the particles of Figure 1.

Figure 3 shows a SEM image of Ti-55Ni particles with diameter around 20 μm.

Figure 4 shows an EDX analysis of the particles of Figure 3.

Figure 5 shows a SEM image of γ-Ti-48AI with sponge shaped particles.

Figure 6 shows an EDX analysis of the particles of Figure 5. Figure 7 shows a SEM image of Ot₂-Ti₃AI with sponge shaped particles.

Figure 8 shows an EDX analysis of the particles of Figure 7.

Figure 9 shows a SEM image of Ti-28Nb particles.

Figure 10 shows an EDX analysis of the particles of Figure 9.

Figure 11 show a SEM image of Ti-24Nb-3AI particles. Figure 12 shows an EDX analysis of the particles of Figure 11.

Figure 13 shows a SEM image of Ti-35Nb-7Zr-5Ta particles.

Figure 14 shows an EDX analysis of the particles of Figure 13.

Figure 15 shows SEM image of Ti-10V-2Fe-3AI particles.

Figure 16 shows an EDX analysis of the particles of Figure 15. Figure 17 shows a SEM image of Ti-6AI-2Sn-4Zr-2Mo particles.

Figure 18 shows an EDX analysis of the particles of Figure 17. Detailed Description

This invention relates to a process for producing high quality titanium alloy powders by reduction of TiO₂ with other alloying metal oxides and/or elemental metals at a temperature range below that of the alloy's melting point, therefore referred to as Solid State Reduction (SSR).

In particular, the present invention relates to a new processing route for the production of a variety of titanium alloys in fine particulate form. The process comprises the homogenization annealing of titanium oxide (TiO₂), followed by the crushing and screening for particle size of the resulting TiO₂. The screened TiO₂ particles of titanium oxide are then mixed with alloying metal oxides and/or elemental metals and calcium hydride (CaH₂). On heating in an inert environment at high temperature, the titanium oxide and alloying metal oxides and/or elemental metals are reduced and alloyed homogeneously. After removal of calcium oxide (CaO) with a washing process, titanium alloy powders are recovered.

This process has advantages over the conventional metallurgical processes that typically involve liquid phase chemical reaction, resulting in costly energy consumption, high wear rate of equipment and inevitable environmental detriment. In contrast, SSR is an energy-efficient, environmental friendly and cost-effective process. In addition, titanium alloys produced by the SSR process feature substantially homogeneous elemental distribution and ultra fine microstructure, substantially avoiding weaknesses commonly associated with melting processes, such as segregation and dendrite structure.

The other advantage of the SSR process is that the particle size of the titanium alloys produced can be predetermined through controlling the particle size of the starting TiO₂ powder. Thus a required particle size from sieving results in desired particle size of alloy powder. As discussed later other factors will also influence this. The SSR process is based on the principle of mass transport in a crystalline solid. It is believed that, during the reduction step, oxygen atoms in the TiO₂ crystal structure diffuse outward in order to combine with active calcium atoms (decomposed from CaH₂) in the surrounding area. Meanwhile, the alloying metal atoms in the vicinity, which are also freshly reduced by CaH₂ from their oxides, diffuse inward into the TVTiO₂ crystal. The degree of purity and homogeneity of the titanium alloy depends on these two opposite diffusions. It has been found by many researchers that the grain size and grain boundary ratio play an important role in the diffusion processes. Commercially available TiO₂ powders normally consist of nano-sized but agglomerated particles and inhomogeneous crystal structures. Thus, diffusion rate and path of each atom involved in reduction and diffusion can be perturbed. The resulting reduction is not consistent or complete throughout the material.

In this invention, a homogenous annealing treatment for TiO₂ is introduced prior to the solid state reduction process. The commercially available TiO₂ powder is heated to a high temperature, preferably between about 1200 to about 1400⁰C, preferably in an inert environment, for approximately about 2 to about 5 hours to coarsen TiO₂ grains and normalise the crystal structure of the TiO₂. An inert environment is not required to achieve this result; however the inventors have found the use of an inert environment (such as argon or vacuum) achieves cleaner results.

An exemplary apparatus for carrying out the homogenous annealing step is to heat the TiO₂ in an alumina crucible within a chamber furnace. However, it will be apparent to those skilled in the art that other apparatus could be used.

The term "homogenization annealing" is used to mean the heating of a substance to high temperature to give substantially even distribution of crystal structure throughout the substance.

The treated TiO₂ is crushed and screened to the required particle size. The crushing can be achieved, for example, using low-energy ball milling or discus mill, preferably low-energy ball milling. The screening can be achieved with the use of a variety of screening devices, preferably using mechanical sieves, as would be known to the skilled person. The TiO₂ powders are selected for further processing by particle size. The final alloy powder particle size distribution can be achieved through selection of the starting particle size distribution as well as reduction parameters. The reduction parameters which will affect the particle size are the temperature at which the mixture of TiO₂, CaH₂ and alloying oxides/metal powders are heated and the amount of time for which they are heated (hold time). Therefore by selecting the particle size of the TiO₂, and selecting reduction parameters together will allow a predetermined particle size of alloy powder to be achieved. However the initial selection of the particle size of TiO₂ is a critical first step. As an illustrative example, the inventors have found that a relatively higher temperature or hold time will result in coarser particle size i.e. larger, for example a hold time of about 6 hours at about 1200°C will result in an alloy powder particle size of up to 100 microns.

The alloying metal oxides and/or elemental metals are selected from but not limited to any one or more of Al, Sn, NiO, V₂O₅, Nb₂O₅, Cr₂O₃, AI₂O₃, ZrO₂, Ta₂O₅, Fe₂O₃, MoO₂ and other similar oxides. The result is at least a bi-compound titanium alloy. If a further metal oxide or elemental metal is used the result can be a tri-compound, or other multi-compound titanium alloy. The stoichiometry of the alloying metal oxides or elemental metals used is calculated based on the percentage of the alloying element required in the final product. For example to produce the alloy Ti-25AI, TiO₂ and Al powder are mixed in the mass ratio of 60.0:6.7. The mass Of CaH₂ added is calculated based on the stoichiometry of oxygen to be reduced in total. An excess of CaH₂ may be added according to different requirements in the final product. Such matters would be well within the abilities of a person skilled in this area, once in possession of this invention.

The annealed, crushed and screened TiO₂ and metal oxides and/or elemental metals are mixed with CaH₂ and heated to a temperature below the melting point of the alloy to be produced. The mixing may be carried out, for example, with low energy ball milling or an ultra-sonic mixer, preferably with low energy ball milling. The mixing may be carried out, for example, for between 10 and 30 minutes, preferably 10 minutes, but time will be dependent on the means used, as would be known to the skilled person. The temperature below the melting point of the alloy is preferably between about 1100⁰C and about 1400⁰C, more preferably between about 1200°C and about 1300°C. The mixing step is preferably carried out in an inert environment (such as argon or vacuum). The heating time should be sufficient to achieve a solid state reduction, preferably at least about two hours, even more preferably between about 2 and about 6 hours. The temperature and time of the solid state reduction step are dependent on the alloy system and particle size required in the final products. Such matters would be well within the abilities of a person skilled in this area, once in possession of this invention. The heating can be carried out in a chamber or tube furnace. The furnace should be capable of retaining the inert environment (if used).

The product of the solid state reduction step is preferably washed to remove CaO. For example it is preferably firstly washed with weak acidic solution, preferably a 10 vol.% of acetic acid solution, to assist in dissolving the CaO produced from the solid state reduction process. The washing step may be repeated as many as about 10 times as required, preferably about 5 times. It should be appreciated other weak acid solutions could be used for this purpose and those skilled in the art would be aware of such acids and washing options. The alloy powder is additionally or alternatively washed with deionised water for as many as about 10 -15 times as required. An alternative method of washing would be the use of a continuous washing process. A centrifuge machine can be employed if desired to intensify and accelerate the washing process. The alloy powder product is then collected and may be dried, preferably with the use of an infrared heating oven, although other suitable options could be used.

An inert environment is typically provided by the use of argon gas or vacuum conditions; however a person skilled in the art will be aware of other methods. The alloy powder recovered from the process is dependent on the metal oxide and/or elemental metal(s) used. Preferably the alloy powder is selected from an alloy of Ti with any one or more of V, Ni, Al, Nb, Zr, Ta, Fe, Zr, Mo and Cr. As exemplified the in examples below many different alloys powders can produced by the method, such as Ti-Al-V, Ti-Ni, Ti-Al, Ti-Nb, Ti-Nb-Al, Ti-Nb-Zr-Ta, Ti-V-Fe-Al, Ti-Al-Sn-Zr-Mo alloys,

In the following examples homogenous annealing treatment Of TiO₂ (Millennium Inorganic Chemicals, commercial pure) was carried out using a reaction chamber device made by a local company from New Zealand (The Electric Furnace Co. Ltd) at 1300⁰C for 4 hours in an Argon atmosphere. Crushing of the resulting TiO₂ was carried out using low energy ball milling using centrifugal ball mills S100 made by Fa. Retsch, Germany. The screening step was carried out using Retsch mechanical shaking sieves.

The mixing of the screened TiO₂ powder (selected for required particle size) with CaH₂ (Commercial grade, 97% purity) and various alloying metal oxides and/or elemental metal powders was carried out using ball milling for 5 minutes. This was followed by heating of the mixture to 1210-1300⁰C for 2-4 hours (temperature and time to achieve the solid state reduction dependent on alloy powder required), using a vacuum chamber furnace made by ElectroFurm Co. NZ

Washing was carried out using 10% acetic acid (Glacial grade, 99% pure) and also de-ionised water. The de-ionised water was produced by an Ion-Exchanger made by the firm Viola (USA).

The analyses of the various powders produced were completed by the University of Auckland - Research Centre for Surface and Material Science, and the Institute for Material Science, Fraunhofer Society, Dresden, Germany. Examples

The present invention will be described in more detail by referring to the following examples but is not deemed to be limited thereto.

TiO₂ powder (Millennium Inorganic Chemicals, commercial pure) was homogenization annealed at 1300⁰C for 4 hours in Ar atmosphere. After 10 min ball milling, the powder was screened and the particle sizes were classified as: 20-63 μm and 63-100 μm.

Example 1. Ti-6AI-4V (wt.%)

TiO₂ powder with particle size ranging between 63-100 μm was mixed with Al (commercial grade 99% 50μm) and V₂O₅ (Sigma-Aldrich 99.6%) powders at mass ratio: TiO₂ : Al : V₂O₅ = 150.0 : 6.0 : 7.1 , then mixed with 1.5 x stoichiometric amount of CaH₂ (commercial pure 97%) by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 1300⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. The scanning electronic microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) analysis of the resultant powder reveals that the powder is Ti-6AI-4V with spherical particle shape, as shown in Figures 1 and 2.

Example 2. Ti-55Ni (wt.%)

TiO₂ powder with particle size ranging between 20-63 μm was mixed with NiO powder (Sigma-Aldrich Ni 76-77%, 10 μm) at mass ratio: TiO₂ : NiO = 70.0 : 69.9, then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 1300⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-55Ni with rounded particle shape, as shown in Figures 3 and 4. Example 3. γ-Ti-48AI (at.%)

TiO₂ powder with particle size ranging between 20-63 μm was mixed with AI₂O₃ powder (Sigma-Aldrich 99.8% <10 μm) at mass ratio: TiO₂ : AI₂O₃ = 41.6 : 24.5, then mixed with 2 x stoichiometric amount of CaH₂ by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 1280⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is γ-Ti-48AI with sponge particle shape, as shown in Figures 5 and 6.

Example 4. Ti-25AI (at.%)

TiO₂ powder with particle size ranging between 20-63 μm was mixed with Al powder (commercial grade 99%, 50 μm) at mass ratio: TiO₂ : Al= 60.0 : 6.7, then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 1280⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-25AI (Ot₂-Ti₃AI) with sponge particle shape, as shown in Figures 7 and 8.

Example 5. Ti-28Nb (at.%) TiO₂ powder with particle size ranging between 20-63 μm was mixed with Nb₂O₅ powder (Sigma-Aldrich 99.9%, 325 mesh) at mass ratio: TiO₂ : Nb₂O₅= 57.6 : 37.2, then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 1210⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-28Nb with sponge particle shape, as shown in Figures 9 and 10.

Example 6. Ti-24Nb-3AI (at.%)

TiO₂ powder with particle size ranging between 20-63 μm was mixed with Nb₂O₅ powder (Sigma-AIdrich 99.9%, 325 mesh) and Al powder (commercial grade 99%, 50 μm) at mass ratio: TiO₂ : Nb₂O₅ : Al = 58.0 : 31.9 : 1 , then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 5 min. The powder mixture was then heated to carry out the SSR process at 121O⁰C for 4 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-24Nb-3AI with sponge particle shape, as shown in Figures 11 and 12.

Example 7. Ti-35Nb-7Zr-5Ta (wt.%) TiO₂ powder with particle size ranging between 20-63 μm was mixed with Nb₂O₅ powder (99.9%, 325) mesh) and ZrO₂ powder (commercial grade 99.9% ) and Ta₂O₅ (commercial grade 99.9%) at mass ratio: TiO₂ : Nb₂O₅ : ZrO₂ : Ta₂O₅= 88.3 : 50.1 : 9.5 : 6.1 , then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 12 min. The powder mixture was then heated to carry out the SSR process at 1210⁰C for 2 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-35Nb-7Zr-5Ta with sponge particle shape, as shown in Figures 13 and 14.

Example 8. Ti-10V-2Fe-3AI (wt.%) TiO₂ powder with particle size ranging between 20-63 μm was mixed with V₂O₅ powder (Sigma-AIdrich 99.6%) and Fe₂O₃ powder (commercial grade 99.9% ) and Al (commercial grade 99.9%) at mass ratio: TiO₂ : V₂O₅: Fe₂O₃: Al = 141.7 : 17.8 : 9.5 : 3 , then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 12 min. The powder mixture was then heated to carry out the SSR process at 128O⁰C for 2 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-10V-2Fe-3AI with spherical particle shape, as shown in Figures 15 and 16.

Example 9. Ti-6AI-2Sn-4Zr-2Mo (wt.%) TiO₂ powder with particle size ranging between 20-63 μm was mixed with Al (commercial grade 99.9%) , Sn powder (Sigma-Aldrich 99.8%, -325 mesh), ZrO₂ powder (commercial grade 99.9% ), MoO₂ (Sigma-Aldrich 99%) at mass ratio: TiO₂ : Al : Sn : ZrO₂ : MoO₂ = 143.3 : 6.0 : 2.0 : 5.4 : 2.7, then mixed with 1.5 x stoichiometric amount of CaH₂ by ball milling for 12 min. The powder mixture was then heated to carry out the SSR process at 1280⁰C for 2 hours in Ar atmosphere. The product of SSR was washed with a 10 vol.% of acetic acid solution 5 times and rinsed with deionised water 15 times. SEM and EDX analysis of the resultant powder reveals that the powder is Ti-10V-2Fe-3AI with spherical particle shape, as shown in Figures 17 and 18.

The results of the Examples provided clearly show the product of a variety of alloys in fine particulate form. The alloys produced also feature substantially homogeneous elemental distribution. The results thus clearly provide the user with advantages such as reducing the impact of segregation and dendrite structure. In addition, the ability to control the particle size of the alloys produced by controlling the particle size of the starting powder allows the user a control feature previously difficult to provide.

The foregoing describes the invention including a preferred form thereof. Alterations and modifications as would be known to a person skilled in this art are intended to be included within the spirit and scope of the invention. The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention.

Claims

What we claim is:

1. A process for the manufacture of multi-compound titanium alloy powder, the method including the following steps:

(a) homogenization annealing Of TiO₂,

(b) crushing and screening the results of (a) to the required particle size,

2. A process according to claim 1 wherein the homogenization annealing in step (a) is carried out at about 1200⁰C to about 1400⁰C.

3. A process according to claim 1 or 2 wherein the homogenization annealing in step (a) is carried out for about 2 to about 5 hours.

4. A process according to any one of claims 1 to 3 wherein the homogenization annealing in step (a) is carried out in an inert environment.

5. A process according to claim 4 wherein the inert environment is an argon or vacuum environment.

6. A process according to any one of claims 1 to 5 wherein the required particle size in step (b) is selected to give a desired particle size of alloy powder.

7. A process according to any one of claims 1 to 6 wherein the crushing is carried out using a ball or discus milling machine.

8. A process according to any one of claims 1 to 7 wherein the screening is carried out using mechanical sieves.

9. A process according to any one of claims 1 to 8 wherein the alloying metal oxide is selected from any one or more of: V₂O₅, NiO, AI₂O₃, Nb₂O₅, Ta₂O₅, Fe₂O₃, ZrO₂,

MoO₂ and Cr₂O₃.

10. A process according to any one of claims 1 to 9 wherein the elemental metal is selected from any one or more of: Al and Sn.

11. A process according to any one of claims 1 to 10 wherein the temperature below the melting point of the alloy in step (c) is greater than about 110O⁰C.

12. A process according to any one of claims 1 to 11 wherein the temperature below the melting point of the alloy in step (c) is between about 110O⁰C and about 1400⁰C.

13. A process according to any one of claims 1 to 12 wherein the temperature below the melting point of the alloy in step (c) is between about 1200⁰C and about 1300°C.

14. A process according to any one of claims 1 to 13 wherein the components in step (c) are heated at a temperature below the melting point of the alloy for at least about two hours.

15. A process according to any one of claims 1 to 14 wherein the components in step (c) are heated at a temperature below the melting point of the alloy for about 2 to about 6 hours.

16. A process according to any one of claims 1 to 15 wherein the components in step (c) are heated at a temperature below the melting point of the alloy in an inert environment.

17. A process according to claim 16 wherein the inert environment is an argon or vacuum environment.

18. A process according to any one of claims 1 to 17 wherein the result of step (c) is washed.

19. A process according to any one of claims 1 to 18 wherein the result of step (c) is washed with weak acidic solution and/or deionised water.

20. A process according to any one of claims 1 to 19 wherein the alloy powder recovered is selected from an alloy of Ti with any one or more of V, Ni, Al, Nb, Zr, Ta, Fe, Zr, Mo and Cr.

21. A process according to any one of claims 1 to 20 wherein the alloy powder recovered is selected from any one or more of: Ti-Al-V, Ti-Ni, Ti-Al, Ti-Nb, Ti-Nb-Al, Ti-Nb-Zr-Ta, Ti-V-Fe-Al, Ti-Al-Sn-Zr-Mo alloys.

22. A process for the manufacture of multi-compound titanium alloy powder, the method including the following steps:

(a)homogenization annealing of TiO₂ at about 1200⁰C to about 1400⁰C, for about 2 to about 5 hours, in an inert environment of argon,

(b) crushing and screening the results of (a) to the required particle size, wherein the required particle size is selected to give a desired particle size of alloy powder,

(c) mixing the result of (b) with alloying metal oxide and/or elemental metal powders and CaH₂ and heating at a temperature of between about 1200⁰C and about 1300⁰C for about 2 to about 6 hours,

(d) washing the result of step (c) with weak acidic solution and/or deionised water, (e) recovering the alloy powder.

23. An alloy powder produced by the process as described in any one of claims 1 to 22.