Manufacture of near-net shape titanium alloy articles from metal powders by sintering with presence of atomic hydrogen

Abstract

Disclosed herein is a process that includes: (a) providing a powder blend comprising (1) one or more hydrogenated titanium powders containing around 0.2 to around 3.4 weight % of hydrogen, and (2) one or more master alloys, comprising Al, V, or a combination thereof, (b) consolidating the powder blend by compacting the powder blend to provide a green compact, (c) heating the green compact to a temperature ranging from around 400° C. to around 900° C., thereby releasing the majority or all of the hydrogen from the hydrogenated titanium, and partially sintering the green compact without fully sintering it, to obtain a partially sintered article having a density of about 60% to about 85% of theoretical density, (d) sizing the partially sintered article at a temperature at or around room temperature to obtain an sized article having a density of about 80% to about 95% of theoretical density, (e) heating the sized article in vacuum thereby sintering the article to form a sintered dense compact having a density of 99% of theoretical density or higher.

Claims

1. A method for the manufacture of near-net shape titanium or titanium alloy articles from metal powders comprising: (a) providing a powder blend comprising (1) one or more hydrogenated titanium powders containing around 0.2 to around 3.4 weight % of hydrogen, and (2) one or more master alloys, comprising Al, V, or a combination thereof, (b) consolidating the powder blend by compacting the powder blend to provide a green compact, (c) heating the green compact to a temperature ranging from around 400° C. to around 900° C., thereby releasing the majority or all of the hydrogen from the hydrogenated titanium, and partially sintering the green compact without fully sintering it, to obtain a partially sintered article having a density of about 60% to about 85% of theoretical density, (d) sizing the partially sintered article at a temperature at or around room temperature to obtain an sized article having a density of about 80% to about 95% of theoretical density, (e) heating the sized article in vacuum thereby sintering the article to form a sintered dense compact having a density of 99% of theoretical density or higher.

2. The method according to claim 1, wherein the sized article exhibits a linear shrinkage of 3% or less during step (e).

3. The method according to claim 1, further comprising subjecting the article obtained from step (e) to (f) hot processing selected from the group consisting of forging, rolling, hot isostatic pressing (HIP), extrusion, and combinations of these.

4. The method according to claim 3, further comprising subjecting the article obtained from step (e) to (g) grinding, or (h) tumbling, or both.

5. The method according to claim 1, wherein the consolidating of the green compact comprises molding of the powder blend.

6. The method according to claim 1, wherein the step (c) results in a material wherein all or most of the hydrogen is emitted, and full sintering of the material has not occurred.

7. The method according to claim 1, wherein the step (c) results in a soft material having a soft titanium matrix within which is evenly distributed a master alloy.

8. The method according to claim 7, wherein the master alloy comprises about 60% Al and about 40% V.

9. The method according to claim 8, wherein the master alloy is present in the titanium matrix in a concentration of about 10%.

10. The method according to claim 1, wherein the step (e) provides a linear shrinkage of about 3% or less.

11. The method according to claim 1, wherein the hydrogenated titanium powder, the master alloy powder, or both, have an average particle size less than about 150 microns.

12. The method according to claim 11, wherein the hydrogenated titanium powder, the master alloy powder, or both, have an average particle size greater than 100 microns.

13. The method according to claim 1, wherein the partially sintered article has an average grain size between about 100 microns and about 150 microns.

14. A near net shape titanium alloy article produced by the process according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The embodiments described herein can be understood by reference to the accompanying drawings, which are intended to be illustrative, rather than limiting.

(2) FIG. 1 is a graph showing the relationship between compaction pressure used to produce a green compact, and the relative density of the sintered articles prepared from Ti powder alone and from Ti powder combined with hydrogenated titanium powder according to an embodiment disclosed herein.

(3) FIG. 2 is a graph showing the relationship between change in free energy and temperature for different hydrogen pressures during sintering according to an embodiment disclosed herein.

(4) FIG. 3 is a schematic diagram illustrating two mechanisms for disappearance of oxide films on surfaces of particles of Ti metal and hydrogenated titanium.

(5) FIG. 4 is a graph showing mass spectrometry curves that illustrate the relationship between released water, hydrogen emission, and temperature for processing according to embodiments disclosed herein.

(6) FIG. 5 is a process flow diagram for production of titanium alloy articles according to an embodiment of the invention.

(7) FIGS. 6a and 6b are micrographs showing the microstructure of a titanium alloy article prepared according to an embodiment of the invention; FIG. 6A shows the microstructure before hot isostatic pressing (HIP), and FIG. 6B shows the microstructure after HIP.

(8) FIGS. 7a and 7b are micrographs showing the microstructure of a titanium alloy article prepared according to another embodiment of the invention; FIG. 7A shows the microstructure before hot isostatic pressing (HIP), and FIG. 7B shows the microstructure after HIP.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(9) The methods described herein can be more clearly understood by reference to the following description of specific embodiments and examples, which are intended to illustrate, rather than limit, the scope of the appended claims.

(10) As used herein, the terms “around” or “about” in connection with a numerical value denote a deviation from the numerical value of ±5%. As used herein, the term “hydrogenated titanium powders” includes titanium powders having hydrogen contents ranging from about 0.2 to about 3.9 wt %. This includes hydrogenated titanium particles nominally described as “titanium hydride” or “TiH.sub.2”, as well as other hydrogenated titanium particles having hydrogen contents within the indicated range, and combinations thereof, unless otherwise indicated. For example, this terminology can include hydrogenated titanium powder containing hydrogen in an amount ranging from 0.2 wt % up to and including 3.4 wt %, as well as hydrogenated titanium powder containing hydrogen in an amount above 3.4 wt % and up to and including 3.9 wt %, the latter being sometimes denominated as “titanium hydride” or “TiH.sub.2 powder.”

(11) As described above, the methods disclosed herein relate generally to the manufacture of sintered titanium and titanium alloys using elemental metal powders and titanium hydride and/or hydrogenated titanium powders as raw materials. It has been found that the atomic hydrogen emitted from titanium hydride and hydrogenated titanium powders before formation of molecular hydrogen plays a very important role in chemical reduction and cleaning of the titanium particles with respect to oxygen and other impurities such as chlorine, magnesium, sodium, and in preventing oxidation during heating and sintering, as well.

(12) Previously known methods, as described above, have not been able to determine the desirable process steps and parameters described herein in order to provide effective action of emitted atomic hydrogen and control of porosity and densification of compacted titanium particles to reach maximum possible density, purity, and mechanical properties of final sintered articles. Previous methods described above have used permanent outgassing of the vacuum chamber during heating and sintering. As a result, a complete reaction between metal powders in green titanium compacts with hydrogen is not achieved, and the final structure of the sintered alloy contains oxides, other impurities, and irregular porosity.

(13) In particular embodiments described herein, one or more of the hydrogenated titanium powders used was compacted to a relatively low density in the green samples (3.06 g/cm.sup.3) as compared to green samples prepared from titanium powder alone (3.47 g/cm.sup.3). However, after sintering, the converse was true, and the C.P.-Ti samples produced using hydrogenated titanium powder had a higher density (4.43 g/cm.sup.3, i.e. 98.2%) than those sintered from Ti powder alone (4.37 g/cm.sup.3, 97.0%). This result confirms the advantage of using hydrogenated titanium powders to form the powder blend with respect to achieving higher sintered density, as shown in FIG. 1, and is contrary to what would have been expected based on, e.g., U.S. Pat. No. 4,560,621. Similar results were obtained for Ti-6Al-4V compositions prepared according to the methods disclosed herein. The influence of the emitted hydrogen on sintered density becomes clear from an analysis of the effects of hydrogenated titanium upon compaction and heating processing stages of the disclosed methods, which determines final density.

(14) The emitted atomic hydrogen beneficially affects sintering kinetics, helps to reduce any oxides that are usually located on the surface of powder particles, and by doing so, is cleaning inter-particle interfaces and enhancing the diffusion between all components of the powder mixture.

(15) We discovered from our experimental studies that the positive effect of emitted hydrogen in titanium sintering can be significantly enhanced by the control of pressure, temperature and time within the sintering process. In particular, we found that the best reduction of surface titanium oxides by emitted atomic hydrogen occurs at particular combinations of the hydrogen pressure and temperature, as shown in FIG. 2.

(16) In FIG. 2, all pressure-temperature combinations below the line of ΔG=0 provide reduction of titanium oxide, while there is no reduction reaction by the emitted atomic hydrogen at the pressure-temperature combinations above this line. This means that permanent outgassing during sintering with titanium hydride (which has been used in prior art methods described above) may result in ineffective reduction of surface titanium oxides from titanium particles, and as a result, in the presence of excessive or undesirably amounts of oxygen in the final sintered product.

(17) Without wishing to be bound by any theory, it is believed that a characteristic feature of the hydrogenated titanium powders used in the methods disclosed herein is the ability to undergo a dehydrogenation process, i.e. a process of hydrogen evolution from the material, and the resulting significant shrinkage during vacuum heating above 320° C. The temperature interval of dehydrogenation and corresponding changes in the phase composition depend on the heating rate and the rate of hydrogen evacuation from the heating chamber. Relatively slow heating (e.g., a heating rate of ≦15° C./min (preferably ˜7° C./min) led to a phase change represented by TiH.sub.2.fwdarw.β.fwdarw.α and which is a consequence of phase transformations, and completion of dehydrogenation at a temperature of about 800° C. The intensity of hydrogen evolution varied within the mentioned temperature range and was determined by diffusion rate of hydrogen in the phases towards the powder particle surface. The most intensive dehydrogenation with evolution of a major portion of hydrogen from the material was observed within a temperature range of about 400 to about 600° C., and is believed to be due to the formation of the β-phase, in which hydrogen diffusivity is the fastest. Decreases in hydrogen concentration are believed to lead to the α-phase formation at temperatures of about 600 to about 650° C. as a final product of dehydrogenation, and to the evolution of a small portion of residual hydrogen from the α phase at further heating up to 800° C.

(18) Significant volume changes in the material that occur during dehydrogenation resulted in a much more considerable shrinkage of compacts prepared using hydrogenated titanium powder as compared to compacts prepared using only titanium metal powder. Shrinkage of compacts prepared using hydrogenated titanium powder is determined by dehydrogenation (below 800° C.) and sintering of powders and the contribution of the latter becomes apparent at the final stage of dehydrogenation and at higher temperatures. By contrast, the volume changes observed for compacts prepared using only titanium metal powders were determined by the mechanism of powder sintering only.

(19) Other positive effects of using hydrogenated titanium powders in the powder blend and compacting the blend are (a) relative independence of final (sintered) density on the green density in different cross-sections of the sintered article, (b) the possibility of varying shrinkage to get the precise desired final article dimensions at near full theoretical density, and (c) the ability to have compaction stresses relaxed in more ductile titanium powder.

(20) We also found that effectiveness of hydrogen cleaning depends on: (a) the state of oxygen in the titanium particles and (b) the type of porosity of the green compact that interacts with emitted atomic hydrogen. We found that the decrease of oxygen content by hydrogen reduction is especially important for powder material in which surface area is highly developed. On the other hand, this mechanism cannot decrease oxygen content if oxygen is in solid solution. FIG. 3 schematically illustrates a competition between two processes involving oxide films on the powder surfaces—either to be reduced by hydrogen or to be dissolved through diffusion of oxygen into the powder interior volume.

(21) We found that the second process proceeds in vacuum at temperatures roughly above 700° C., but in this case oxygen goes inside and remains in the material. As a result, the first process (reducing by hydrogen) should proceed before the oxide dissolution. Therefore it is important to have hydrogen release from the powder particles and the respective reaction of oxide reducing before the oxide film dissolution in the titanium particle body. Control of the sintering thermal cycle by control of the heating rate and of the holding step in the temperature range of about 400 to about 600° C. significantly improve cleaning of oxygen from the particles of the titanium green compact.

(22) The second feature of the hydrogen cleaning process occurring in the methods disclosed herein is transformation of open porosity to closed porosity. It has been found that this also happens at temperatures of around 700° C. After this, products of reacting hydrogen with surface impurities will be located inside of the titanium material, and either the reaction will stop due to excessive pressure in the closed pore, or the reaction products will dissolve themselves in titanium instead of reacting with hydrogen at the surface. This relates especially to magnesium and magnesium chloride impurities that should evaporate at the higher temperature of sintering.

(23) As a result, the transformation of open porosity to closed porosity should be delayed until as late as possible in order to reach a high grade of cleaning of all impurities. This can be done by control of the heating rate at a temperature below 700° C. to reserve a part of the hydrogen for reacting at higher temperatures and providing holding steps at temperatures below those at which closing of pores occurs.

(24) One more very important feature of using hydrogenated titanium powders as described herein is the release of H.sub.2O that we observed within the interval of hydrogen emission illustrated by FIG. 4. FIG. 4, shows mass-spectrometry curves of H.sub.2O and H.sub.2 gas release upon heating of titanium metal powdered compacts (curve Ti) and compacts prepared from hydrogenated titanium powders (curve TiH.sub.2). A low-temperature H.sub.2O peak is present for both the TiH.sub.2 and Ti compacts and, without wishing to be bound by theory, is believed to be related to the atmospheric moisture absorbed on the powders. However, another H.sub.2O peak was observed in the curve for the TiH.sub.2 compact above 400° C., but absent from the curve for the Ti compact. The emission of H.sub.2O during hydrogen evolution (indicated by the third curve) can be explained by the reduction of surface oxide scales and cleaning of the powder particle surfaces by emitted atomic hydrogen evolved according to the reaction: TiO.sub.2+4H.fwdarw.Ti+2H.sub.2O.

(25) The dehydrogenation during the heating step, with the resulting phase transformations, volume changes, and reduction of surface oxides, is a distinct feature of the use of hydrogenated titanium powders as described herein, and has beneficial consequences which affect the sintering and properties of final material.

(26) The alpha-beta phase transformations and significant shrinkage due to decrease in hydrogen concentration results in an increased amount of crystal lattice defects, and, hence, activation of diffusion processes. The high specific surface area of hydrogenated titanium powders that are crushed upon compaction also contributes to an acceleration of diffusion and improved sintering at further heating. Moreover, a cleaning effect of hydrogen evolved has two useful consequences.

(27) The oxide scales at powder surfaces are effective barriers for diffusion, which can prevent or limit the sintering of compacted particles. For titanium powder, sintering becomes possible above ˜700° C. when dissolution of TiO.sub.2 scales occurs due to diffusion of oxygen atoms from the surface deep into the titanium. For hydrogenated titanium powders, hydrogen leaving a particle reduces the surface oxide scales (at least partially) before their dissolution and diffusion into the titanium particle, thus promoting a mass transfer between particles and decreasing oxygen content in dehydrogenated titanium.

(28) As a positive effect of all these factors, dehydrogenation as described herein resulted in the formation of highly activated titanium and its improved sintering as compared to a common Ti powder. It can be seen from FIG. 1 that above 800° C., when dehydrogenation is already completed, the initially hydrogenated compact demonstrated noticeably more active shrinkage than the sample made from titanium metal powder. It is believe that first diffusion contacts between hydrogenated titanium particles formed under heating already at 710° C., i.e. before the dehydrogenation completion.

(29) In order to enhance the above mentioned effect of alpha-beta phase transformation, we have found that thermal cycling in the temperature range of about 800 to about 900° C. is advantageous. Without wishing to be bound by theory, it is believed that this helps to accumulate crystal defects for additional activation of sintering titanium particles.

(30) In addition, we found that methods for hot processing of the sintered titanium compact, such as forging, rolling, HIP, and/or extrusion, followed by vacuum annealing at temperatures of around 700 to around 750° C., results in further decrease of the content of residual hydrogen to below 150 ppm.

(31) Optionally, the powder blend can comprise only hydrogenated titanium powders having the hydrogen contents described above, i.e., that contain different amounts of hydrogen in the range of 0.2-3.9 wt. %, for example, a powder blend that comprises three hydrogenated titanium powders with 0.2 wt. % of hydrogen, 2.0 wt. % of hydrogen, and 3.8 wt. % of hydrogen, respectively. During processing according to the embodiments described herein, it is believed that a powder having the lowest content of hydrogen becomes pure titanium powder due to dehydrogenation at an early point of the sintering process.

(32) The embodiments of the process of the manufacture of net-shape titanium and titanium alloy articles described herein and the effects and features of sintering titanium particles in presence of atomic hydrogen that we found experimentally allow the manufacture of sintered titanium and titanium alloy articles with extremely low content of oxygen, hydrogen, and other impurities that meet industrial requirements of ASM and ASTM specifications, e.g.: less than 0.2 wt. % of oxygen, less than 0.006 wt. % of hydrogen, less than 0.05 wt. % of chlorine, less than 0.05 wt. % of magnesium, and wherein the resulting sintered titanium article has a final porosity less than 1.5% at pore sizes less than 20 microns. Low interstitial content made these titanium and titanium alloys weldable, which was not enabled in previously produced powder metallurgy alloys.

(33) The resulting sintered articles have high mechanical properties such as tensile strength, yield strength, and elongation meet or exceed the requirements of the above specifications as indicated in the examples.

(34) 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 technology disclosed herein.

Example 1

(35) A powder blend of three hydrogenated titanium powders containing different amount of hydrogen was used: (1) 25% of hydrogenated titanium powder containing 0.5 wt. % of hydrogen, particle size <45 microns, (2) 25% of hydrogenated titanium powder containing 2 wt. % of hydrogen, particle size <100 microns, and (3) 50% of titanium hydride TiH.sub.2 powder containing 3.8 wt. % of hydrogen, particle size <120 microns. These powders were mixed together, and the obtained mixed powder was compacted at 720 MPa to a low density green compact of 3.05 g/cm.sup.3.

(36) The green compact, having the thickness 12 mm, was heated to 250° C. at a slow heating rate of ˜7° C./min and held at this temperature for 40 min to release absorbed water from the titanium powder. Then, heating was continued at the heating rate of ˜22° C./min to a temperature in the range of 480-500° C. in the atmosphere of emitted hydrogen, and held at this temperature for 30 min to form β-phase titanium and to release reaction water from the hydrogenated titanium powders.

(37) Almost complete reduction of surface oxides of the green compact particles by emitted atomic hydrogen was carried out by further heating the green compact to a temperature of 630° C. and holding at this temperature for 45 min, when the green compact still had open porosity structure. At the same time, β-phase titanium was transformed to α-phase titanium.

(38) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 820° C. with a heating rate of 7° C./min and holding at this temperature for 30 min, which resulted in densification of the green compact to a density of 4.44 g/cm.sup.3 due to completion of dehydrogenation and active shrinkage of the green compact.

(39) Then, heating of the cleaned and refined green compact was continued in a vacuum of 10.sup.−4 Torr at a heating rate of 5-10° C./min to a temperature 1220° C., followed by holding at this temperature for 3.5 hours to form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(40) The titanium plate was hot rolled to the thickness of 8 mm, followed by vacuum annealing at 750° C. for 1.5 hours.

(41) The measured contents of impurities in the final product were the following: oxygen <0.15 wt. %, hydrogen <0.005 wt. %, chlorine <0.001 wt. %, magnesium <0.003 wt. %, sodium <10 ppm.

(42) Standard specimens for mechanical testing were cut and machined from the titanium plate, which has a refined microstructure. Mechanical properties of the manufactured titanium plate were found to be: ultimate tensile strength 552-571 MPa, yield strength 489-510 MPa, and 21-23% elongation.

Example 2

(43) A powder blend of two types of powders was used: (1) 20% of CP titanium powder, which does not contain hydrogen at all, particle size <150 microns, and (2) 80% of titanium hydride TiH.sub.2 powder containing 3.5 wt. % of hydrogen, particle size <100 microns.

(44) These powders were mixed together, and the obtained mixed powder was compacted at 780 MPa to a low density green compact of 3.24 g/cm.sup.3.

(45) The green compact having the thickness 24 mm was heated to 230° C. at a slow heating rate of ˜7° C./min and held at this temperature for 80 min to release absorbed water from the powder. Then, heating was continued at the heating rate of ˜22° C./min to 560-580° C. in the atmosphere of emitted hydrogen and held at this temperature for 25 min to form β-phase titanium and release reaction water from the powder.

(46) Almost complete reduction of surface oxides of green compact particles by emitted atomic hydrogen was carried out by further heating the green compact to 700° C. and holding at this temperature for 35 min when the green compact still had open porosity structure. At the same time, β-phase was transformed to α-phase titanium.

(47) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 830° C. with the rate of 7° C./min and holding at this temperature for 20 min that was resulted in densification of green compact to 4.41 g/cm.sup.3 due to complete dehydrogenation and active shrinkage of compact containing both titanium and titanium hydride components.

(48) Then, heating of the cleaned and refined green compact was continued in vacuum of 10.sup.−4 Torr at the rate of 5-10° C./min to the temperature 1240° C. followed by holding at this temperature for 4 hours to form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(49) The titanium plate was hot rolled to the thickness of 20 mm followed by vacuum annealing at 720° C. for 3.5 hours.

(50) Measured contents of impurities in the final product were the following: oxygen <0.14 wt. %, hydrogen <0.006 wt. %, chlorine <0.001 wt. %, magnesium <0.004 wt. %, sodium <10 ppm.

(51) Standard specimens for mechanical testing were cut and machined from the titanium plate, which has a refined microstructure. Mechanical properties of the manufactured titanium plate were: ultimate tensile strength 567-582 MPa, yield strength 498-526 MPa, and 18-20% elongation.

Example 3

(52) A powder blend of three types of powders was used: (1) 70 wt. % of titanium hydride powder TiH.sub.2 containing 3.8 wt. % of hydrogen and having particle size less than 120 μm, (2) 20% wt. % of CP titanium powder, which does not contain hydrogen, particle size <150 microns, and (3) 10 wt. % of the 60Al-40V master alloy powder having particle size <65 μm.

(53) These powders were mixed together, and the obtained mixed powder was compacted at 960 MPa to a low density green compact of 3.46 g/cm.sup.3.

(54) The green compact having the thickness 16 mm was heated to 250° C. at a slow heating rate of ˜7° C./min and held at this temperature for 50 min to release absorbed water from the powders. Then, heating was continued at a heating rate of ˜20° C./min to 580-600° C. in the atmosphere of emitted atomic hydrogen and held at this temperature for 30 min to form β-phase titanium and release reaction water from the powder.

(55) Almost complete reduction of surface oxides of green compact particles by emitted hydrogen was carried out by further heating the green compact to 680° C. and holding at this temperature for 50 min when the green compact still had open porosity structure. At the same time, β-phase titanium was transformed to α-phase titanium.

(56) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 850° C. with the rate of 7° C./min and holding at this temperature for 30 min that was resulted in densification of green compact to 4.47 g/cm.sup.3 due to complete dehydrogenation and active shrinkage of the compact containing both titanium and hydrogenated titanium components.

(57) Then, heating of the cleaned and refined green compact was continued in vacuum of 10.sup.−4 Torr at the rate of 5-10° C./min to the temperature 1250° C. followed by holding at this temperature for 4.5 hours to form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(58) The titanium alloy Ti-6Al-4V plate was hot rolled to the thickness of 12 mm followed by vacuum annealing at 750° C. for 3 hours.

(59) Measured contents of impurities in the final product were the following: oxygen <0.15 wt. %, hydrogen <0.0055 wt. %, chlorine <0.001 wt. %, magnesium <0.004 wt. %, sodium <10 ppm.

(60) Standard specimens for mechanical testing were cut and machined from the titanium alloy plate, which has a refined microstructure. Mechanical properties of the manufactured titanium plate were: ultimate tensile strength 979-1041 MPa, yield strength 889-910 MPa, and elongation at break 15-18%. Due to low content of contaminants, the resulting titanium alloy plate is weldable using both GTAW and GMAW arc welding technique.

Example 4

(61) A powder blend of two types of powders was used: (1) 20 wt. % of underseparated titanium powder containing 2.0% chlorine and 0.8% of magnesium and having particle size <100 μm, and (2) 80 wt. % of titanium hydride TiH.sub.2 powder containing 3.9 wt. % of hydrogen, particle size <100 microns.

(62) These powders are blended for 6 hours, and the obtained mixed powder was compacted at 400 MPa to a low density green compact of 3.18 g/cm.sup.3.

(63) The green compact having a thickness 20 mm was heated to 250° C. at a slow heating rate of ˜7° C./min and held at this temperature for 70 min to release absorbed water from titanium powder. Then, the net-shaped green compacts were exposed to a temperature of 350° C. for 60 min during heating in vacuum furnace for evacuation of chlorine and magnesium from the material.

(64) Further, heating was continued at the heating rate of ˜16° C./min to 400-420° C. in the atmosphere of emitted hydrogen and held at this temperature for 30 min to form β-phase titanium and release reaction water from the powder.

(65) Almost complete reduction of surface oxides of green compact particles by emitted atomic hydrogen was carried out by further heating the green compact to 600-610° C. and holding at this temperature for 45 min when the green compact still had open porosity structure. At the same time, β-phase titanium was transformed to α-phase titanium.

(66) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 800-820° C. with a heating rate of 6-7° C./min and holding at this temperature for 30 min that was resulted in densification of green compact to 4.42 g/cm.sup.3 due to complete dehydrogenation and active shrinkage of compact containing both titanium and hydrogenated titanium components.

(67) Then, heating of the cleaned and refined green compact was continued in vacuum of 10.sup.−4 Torr at the rate of 5-10° C./min to the temperature 1350° C. followed by holding at this temperature for 2 hours to form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(68) The titanium plate was hot rolled to the thickness of 15 mm followed by vacuum annealing at 750° C. for 3 hours.

(69) Measured contents of impurities in the final product were the following: oxygen <0.16 wt. %, hydrogen <0.005 wt. %, chlorine <0.0015 wt. %, magnesium <0.0048 wt. %, sodium <10 ppm.

(70) Standard specimens for mechanical testing were cut and machined from the titanium plate. Mechanical properties of the manufactured titanium plate were: ultimate tensile strength 558-575 MPa, yield strength 461-494 MPa, and elongation at break 21-23%. Due to low content of contaminants, the resulting titanium plate is weldable using both GTAW and GMAW arc welding technique.

Example 5

(71) A powder blend of three types of base powders were used: (1) Crushed hydrogenated titanium sponge TG-110 grade of Zaporozhye Titanium & Magnesium Corp., Ukraine, (2) Titanium hydride TiH.sub.2 powder produced by a new “Non-Kroll” process combining reduction and distillation (ADMA hydrogenated powder), and (3) CP titanium powder manufactured by dehydration of TiH.sub.2. All powders had particle size <100 microns, at the average particle size of 40 microns. Titanium hydride powder contained 3.5% of hydrogen.

(72) These powders were mixed together at the weight ratio of hydrogenated titanium powder (crushed hydrogenated titanium sponge and titanium hydride) to CP titanium of 90% to 10%.

(73) The obtained mixed powder was compacted at 640 MPa to a low density green compact of 3.15 g/cm.sup.3, which is significantly less than that of compacts produced only from CP titanium powder.

(74) The green compact having the thickness 18 mm was heated to 250° C. at a slow heating rate of ˜7° C./min and held at this temperature for 60 min to release absorbed water from the powder. Then, heating was continued at the heating rate of ˜17° C./min to 550-570° C. in the atmosphere of emitted hydrogen and held at this temperature for 30 min to form β-phase titanium and release reaction water from the powder.

(75) Almost complete reduction of surface oxides of the powder by emitted atomic hydrogen was carried out by further heating the green compact to 650° C. and holding at this temperature for 60 min when the green compact still had open porosity structure. At the same time, β-phase titanium was transformed to α-phase titanium.

(76) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 840° C. with the rate of 7° C./min and holding at this temperature for 30 min that resulted in densification of the green compact to 4.43 g/cm.sup.3 due to complete dehydrogenation and active shrinkage of the compact containing both CP titanium powder and hydrogenated titanium component.

(77) Then, heating of the cleaned and refined green compact was continued in vacuum of 10.sup.−4 Torr at the rate of 5-10° C./min to the temperature 1250° C. followed by holding at this temperature for 4 hours form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(78) The titanium plate was hot rolled to the thickness of 12 mm followed by vacuum annealing at 750° C. for 2 hours.

(79) Measured contents of impurities in the final product were the following: oxygen 0.158 wt. %, hydrogen 0.0054 wt. %, chlorine <0.001 wt. %, magnesium 0.004 wt. %, sodium <10 ppm.

(80) Standard specimens for mechanical testing were cut and machined from the titanium plate. Mechanical properties of the manufactured titanium plate were: ultimate tensile strength 544-580 MPa, yield strength 449-467 MPa, and elongation at break 20-21%.

Example 6

(81) A powder blend of four types of powder was used: (1) 20 wt. % of underseparated titanium powder containing 2.0% chlorine and 0.8% of magnesium and having particle size <100 μm, (2) 20 wt. % of underseparated and hydrogenated titanium powder containing 2% of hydrogen, (3) 20 wt. % of C.P. titanium powder, (4) 30 wt. % of titanium hydride TiH.sub.2 powder containing 3.4% of hydrogen, particle size <100 microns, and (5) 10 wt. % of the 60Al-40V master alloy powder having particle size <65 μm.

(82) These powders are blended for 6 hours, and the obtained mixed powder was compacted at 800 MPa to a low density green compact of 3.51 g/cm.sup.3.

(83) The green compact having a thickness of 20 mm was heated to 250° C. at slow heating rate ˜7° C./min and held at this temperature for 70 min to release absorbed water from the powder. Then, net-shaped green compacts were exposed at 350° C. for 60 min during heating in vacuum furnace for evacuation of chlorine and magnesium from the material.

(84) Further, heating was continued at the heating rate of ˜16° C./min to 500-520° C. in the atmosphere of emitted hydrogen and held at this temperature for 30 min to form β-phase titanium and release reaction water from the powder.

(85) Almost complete reduction of surface oxides of green compact particles by emitted atomic hydrogen was carried out by further heating the green compact to 630-650° C. and holding at this temperature for 40 min when the green compact still had open porosity structure. At the same time, β-phase titanium was transformed to α-phase titanium.

(86) Further, the diffusion-controlled chemical homogenization was carried out by heating of green compact to 820-840° C. with the rate of 6-7° C./min and holding at this temperature for 30 min that was resulted in densification of green compact to 4.44 g/cm.sup.3 due to complete dehydrogenation and active shrinkage of compact containing both titanium and hydrogenated titanium components.

(87) Then, heating of the cleaned and refined green compact was continued in vacuum of 10.sup.−4 Torr at the rate of 5-10° C./min to a temperature of 1300° C. followed by holding at this temperature for 2 hours to form a sintered dense compact, and finally, cooling the sintered compact was done to obtain a flat titanium plate.

(88) The titanium plate was hot rolled to the thickness of 15 mm followed by vacuum annealing at 750° C. for 3 hours.

(89) Measured contents of impurities in the final product were the following: oxygen <0.15 wt. %, hydrogen <0.005 wt. %, chlorine <0.0015 wt. %, magnesium <0.0044 wt. %, sodium <10 ppm.

(90) Standard specimens for mechanical testing were cut and machined from the titanium plate. Mechanical properties of the manufactured titanium plate were: ultimate tensile strength 968-1033 MPa, yield strength 881-904 MPa, and elongation at break 15-17%.

Example 7

(91) Approximately 200 articles of various shapes were produced by the following process. A powder blend of titanium hydride powder (ADMATAL™ from ADMA Products, Inc.), in an amount sufficient to provide 90% by weight of Ti, and master alloy powder (60% Al-40% V) in an amount sufficient to provide 10% by weight of master alloy was blended together to achieve an alloy having a stoichiometry of Ti-6Al-4V (90% Ti, 6% Al, and 4% V). The resulting mixture was prepared and processed by die pressing using the following parameters: ramp speed—0.15-0.02 IPS; compacting pressure 40-50 tsi (551-690 MPa); compression dwell time—1-15 sec.; green density 70-86%; to form a green pre-form. The composition of the titanium hydride powder is given in Table 1 below:

(92) TABLE-US-00001 TABLE 1 Material Fe Cl N C Si Ni O H Ti TiH.sub.2 0.070 0.060 0.030 0.010 0.010 0.030 0.100 3.35 Bal Powder

(93) The articles were divided into two groups, and processed differently. In one group (Lot 1), the green pre-form was dehydrogenated and partially sintered according to an embodiment of the invention, using a heating RAMP of 3-20 C/min, and a temperature of dehydrogenation of 750 C-850 C. The dehydrogenated and partially sintered articles were then sized, using a ramp speed—0.15-0.02 IPS; sizing pressure 45-55 tsi (551-690 MPa); compression dwell Time—1-15 sec.; and green density >92%, and then subjected to high temperature vacuum sintering to finally densify the article using a heating RAMP of 3-20 C/min; a temperature of sintering of 1200° C. over 4 hours, and obtaining a sintered density of 0.155 lbs/inch.sup.3. The resulting articles were then subjected to post-processing, including hot isostatic pressing (HIP), grinding, and tumbling.

(94) In the other group of articles (Lot 2), the green pre-form was dehydrogenated and partially sintered according to an embodiment of the invention using the same parameters as for Lot 1. The dehydrogenated and partially sintered articles were then sized, also using the same parameters as for Lot 1, and then subjected to high temperature vacuum sintering to finally densify the article using a heating RAMP of 3-20° C./min; a temperature of sintering of 1315° C. for 4 hours, and obtaining a sintered density of 0.157 lbs/inch.sup.3. The resulting articles were then subjected to post-processing, including hot isostatic pressing (HIP), grinding, and tumbling.

(95) The various parts were evaluated for oxygen and hydrogen contents, density, and microstructure before and after being subjected to HIP.

(96) The microstructure of the articles prepared according to the procedure described above for Lot 1 is shown in FIG. 6A before HIP, and in FIG. 6B after HIP. Additionally, articles were prepared as test specimens for ASTM test E8-13, i.e., as standard 0.500 inch Round Tension Test Specimens with 2 inch Gauge Length, machined from the Ti-6Al-4V alloy articles produced as described above. The Lot 1 specimens were tested for oxygen content, hydrogen content, and density are given in Table 2 below.

(97) TABLE-US-00002 TABLE 2 Density, lbs/inch.sup.3 Vacuum Vacuum Oxygen, Hydrogen, Ti-6A1-4V Sintering Sintering/HIP wt. % ppm Lot # 1 0.155 0.160 0.28 <10
The results of testing the Lot 1 specimens for tensile strength, yield strength, elongation, and reduction in area are given below in Table 3 below.

(98) TABLE-US-00003 TABLE 3 Tensile Test S-141029-059-1 S-141029-060-1 S-141029-061-1 Tensile Strength 146,000 147,000 147,000 (PSI) Yield Strength 129,000 131,000 129,000 0.2% Offset (PSI) Elongation in 16 16 17 4D (%) Reduction of 36 28 36 Area (%) Test Direction Longitudinal Longitudinal Longitudinal Test Method ASTM E8-13a ASTM E8-13a ASTM E8-13a

(99) The microstructure of the articles prepared according to the procedure described above for Lot 2 is shown in FIG. 7A before HIP, and in FIG. 7B after HIP. Additionally, articles were prepared as test specimens for ASTM test E8-13, i.e., as standard 0.500 inch Round Tension Test Specimens with 2 inch Gauge Length, machined from the Ti-6Al-4V alloy articles produced as described above. The Lot 2 specimens were tested for oxygen content, hydrogen content, and density are given in Table 4 below.

(100) TABLE-US-00004 TABLE 4 Density, lbs/inch.sup.3 Vacuum Vacuum Oxygen, Hydrogen, Ti-6A1-4V Sintering Sintering/HIP wt. % ppm Lot # 2 0.157 0.160 0.28 <10
The results of testing the Lot 2 specimens for tensile strength, yield strength, elongation, and reduction in area are given below in Table 5 below.

(101) TABLE-US-00005 TABLE 5 Tensile Test S-141029-062-1 S-141029-063-1 S-141029-064-1 Tensile Strength 147,000 147,000 146,000 (PSI) Yield Strength 130,000 128,000 128,000 0.2% Offset (PSI) Elongation in 17 16 16 4D (%) Reduction of 33 33 33 Area (%) Test Direction Longitudinal Longitudinal Longitudinal Test Method ASTM E3-13a ASTM E8-13a ASTM E8-13a

(102) The chemical composition of the finished parts prepared according to the methods described above is provided in Table 6 below.

(103) TABLE-US-00006 TABLE 6 Tests Results/Units Method Al  5.86% Optical Emission Spectroscopy C 0.0064% Leco Furnace Cl 0.0061% Pyrohydrolysis followed by Ion Chromatography Fe  0.15% Optical Emission Spectroscopy H 0.0005% Leco Furnace Mg  0.002% ICP-MS N  0.026% Leco Furnace Na <0.005% ICP-MS O  0.29% Leco Furnace Others Each  <0.05% Optical Emission Spectroscopy Others Total  <0.15% Optical Emission Spectroscopy Si  0.011% Optical Emission Spectroscopy V  4.00% Optical Emission Spectroscopy Y <0.002% Optical Emission Spectroscopy

(104) The invention have been thus explained and described by reference to certain specific embodiments and examples, it will be appreciated that these specific embodiments and examples are illustrative, rather than limiting of the appended claims.