Tungsten / molybdenum alloys prepared by in-situ dehydrogenation and deep deoxidation of hydrides and methods thereof

Abstract

The application discloses a tungsten / molybdenum alloy prepared by in-situ dehydrogenation and deep deoxidization of hydride and a method thereof, and particularly relates to the following steps: tungsten / molybdenum alloy powder and metal hydride are fully mixed according to a hydride addition amount of 1% to 10% of the total mass of the tungsten / molybdenum alloy powder, then the mixture is pressed into a compact, the compact is placed into a sintering furnace, vacuum in the furnace is extracted, the sintering furnace is heated for vacuum degassing, after the first removal of free oxygen and water vapor in the compact is completed, dry hydrogen is introduced into the sintering furnace and the sintering furnace is heated, under the action of negative pressure, hydrogen enters the voids in the compact, after the second removal of oxygen in the compact is completed, the sintering furnace is continuously heated in a stepwise manner and is kept warm, the temperature is increased to above the dehydrogenation temperature of the metal hydride, the third in-situ dehydrogenation and deep deoxidization of the hydride is completed, and finally the sintering furnace is cooled to obtain a low-oxygen tungsten / molybdenum alloy. The preparation method is simple, the deoxidization efficiency is high, the sintering grain can be significantly refined, the oxygen content in the alloy can be reduced, and the material performance can be improved.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy materials, specifically to a method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides. Background Technology

[0002] Tungsten and molybdenum are both refractory metals with high-temperature resistance. They possess excellent thermal and electrical conductivity, low coefficient of thermal expansion, high-temperature strength, low vapor pressure, and wear resistance, making them important materials for applications in the electronics and power equipment manufacturing industry, metal processing industry, glass manufacturing industry, high-temperature furnace structural component manufacturing, aerospace, and defense industries.

[0003] Tungsten / molybdenum (TMC) metals are body-centered cubic metals, inherently brittle, making forming and deformation particularly difficult. Oxygen, as a significant interstitial element, is often stored at the internal grain boundaries of metallic materials, severely weakening grain boundary bonding strength and significantly increasing the ductile-brittle transition temperature, making deformation of TMC and its alloys even more difficult and frequently leading to brittle fracture. Therefore, this severely restricts the preparation and application of TMC and its alloys. A major reason for the low ductility of TMC and its alloys (and some other BCC alloys) is their sensitivity to certain solutes (such as O and N) unavoidable in commercial products, especially when these impurities segregate at grain boundaries. Therefore, methods to modify grain boundaries and solute distribution can affect strength and ductility. In this regard, second-phase particles (such as carbides and oxides) can play a major role. They can refine grains by promoting grain nucleation and hindering grain growth. A fine microstructure not only significantly improves strength but also creates abundant grain boundary regions, thereby reducing the concentration of harmful solutes in the lattice. Therefore, reducing the oxygen content of impurities at grain boundaries and ensuring uniform doping of second-phase oxide particles are of great significance for improving the performance of tungsten / molybdenum and their alloys.

[0004] To improve the processing performance of tungsten / molybdenum and their alloys and promote their wider application, industry professionals have conducted research on material purification using physical and chemical methods. This has continuously improved the purity of tungsten / molybdenum metal powders and eliminated the effects of various harmful elements, achieving positive progress. However, the processing difficulties of tungsten / molybdenum and their alloys remain significant. In the last century, with the development of alloying technology, dispersion-strengthened rare-earth alloys, silicon-aluminum-potassium tungsten / molybdenum alloys, and solid-solution-strengthened tungsten-rhenium alloys gradually emerged, significantly improving the processing performance of these materials and greatly expanding their application areas. With the increasing size, precision of processing, and longer application duration of tungsten / molybdenum and their alloys, processing problems have resurfaced. Especially with the emergence of applications under harsh conditions, such as high-temperature creep, irradiation, and corrosion, the focus on the oxygen content of tungsten / molybdenum and their alloys has significantly increased. Currently, the oxygen content of tungsten / molybdenum and their alloys is generally at the 30-50 ppm level. With decreasing material size or increasing sintering temperature and time, the oxygen content has relatively decreased to the 30 ppm level. Achieving levels below 30 ppm is extremely difficult, especially for large-scale materials. Unfortunately, the trend towards larger material sizes has become mainstream. Therefore, further reducing the oxygen content of tungsten / molybdenum and their alloys is urgently needed.

[0005] Reducing oxygen content has always been a goal pursued in tungsten / molybdenum and their alloys, as well as powder metallurgy materials. Traditional deoxidation methods involve adjusting the sintering process, slowing the heating rate, and extending the sintering time to reduce oxygen levels before the sintered body densifies. However, progress has been slow. To further improve material properties and meet deoxidation requirements, several commonly used technologies have emerged, including hydrogen pre-reduction and carbon addition deoxidation. A brief introduction follows:

[0006] Powder pre-reduction technology: Given the difficulty in controlling the oxygen content of tungsten / molybdenum and their alloy sintered materials, in order to reduce the pressure on deoxidation during the sintering process, the raw tungsten / molybdenum powder or its alloy powder is reduced again to lower the oxygen content in the raw materials, thereby achieving the target of low oxygen content in the final sintered blank. Based on powder pre-reduction technology, low-oxygen molybdenum powder and tungsten powder have been developed, which significantly reduce the oxygen content of the sintered body.

[0007] Carbide deoxidation technology: Adding carbon (C) to tungsten / molybdenum powder or its alloy powder allows it to react with oxides in the compact during sintering, achieving significant deoxidation. TZM alloy achieves low oxygen levels through carbon deoxidation. Given the significant deoxidation effect of carbon, researchers have also achieved significant results by utilizing the uniform doping properties of organic carbon, such as liquid stearic acid. However, carbon deoxidation can simultaneously generate brittle second phases like tungsten carbide or molybdenum carbide, affecting the properties of tungsten / molybdenum and its alloys. Therefore, the key challenge is to leverage the benefits of carbon reduction while eliminating the drawbacks of carbide formation.

[0008] Alloying: By doping with rare earth oxides, such as lanthanum oxide, yttrium oxide, or cerium oxide, and their composites, rare earth tungsten / molybdenum and their alloys are formed, significantly improving the strength and toughness of the materials. There are two main reasons for this: first, the rare earth oxides, acting as a second phase, significantly refine the grain size of the sintered body, playing a grain-refining role; second, the significant grain refinement greatly increases the grain boundary area, significantly dilutes the grain boundary oxygen content, improves grain boundary bonding performance, and enhances the strength and toughness of tungsten / molybdenum and their alloys.

[0009] Oxygen in tungsten / molybdenum and their alloys mainly originates from the raw material powder. The oxygen content of molybdenum and tungsten powder is generally around 1000 ppm; low-oxygen molybdenum or tungsten powder typically has an oxygen content of around 600 ppm; reports of molybdenum or tungsten powder with oxygen content below 300 ppm are rare. Tungsten / molybdenum powder undergoes a sintering process after molding; the sintering process is both a densification process and a core deoxidation process. Generally, after sintering, the oxygen content in tungsten / molybdenum metal powder decreases from around 1000 ppm to around 30-50 ppm. The oxygen content varies considerably in tungsten / molybdenum and their alloys due to different doping compositions. The aforementioned powder pre-reduction technology, combined with the sintering process, can be viewed as a continuous high-temperature reduction process; theoretically, as long as the temperature is high enough and the time is long enough, significant deoxidation can be achieved. However, high-temperature, long-duration deoxidation is not only uneconomical but also causes excessively large grains, affecting billet performance. Carburization deoxidation involves adding carbon to the billet in a hydrogen environment to reduce oxides and achieve deoxidation. However, carbon is not only a reducing agent but also a combining agent, readily reacting with tungsten / molybdenum powder to produce harmful brittle carbides. Therefore, in production practice, it is only used in the preparation of TZM alloy materials. Alloying deoxidation is another technique, which increases the grain boundary area to dilute the oxygen concentration and reduce its impact on grain boundary strength.

[0010] However, even with the above methods, high-temperature sintering of tungsten / molybdenum metal in a hydrogen environment for approximately 50-60 hours cannot completely deoxidize it. This is because the sintering process of tungsten / molybdenum is carried out under normal pressure, and the process is as follows: tungsten / molybdenum compact is fed into the furnace—air replacement—hydrogen gas introduction—heating—sintering—cooling—unloading—tungsten / molybdenum sintered material. During this process, the tungsten / molybdenum compact, as a porous body, enters the hydrogen environment. Because there is no pressure difference between the inside and outside of the compact during the furnace feeding stage, the pressure is balanced between the air stored inside the porous compact and the hydrogen gas outside the compact. In the low-temperature sintering stage, the compact's porosity shrinks less, and the exchange of gases between the inside and outside of the compact can only occur through... During the Brownian motion phase, hydrogen diffusion is limited. In the mid-temperature and later sintering stages, as the temperature gradually increases and the volume of the compact's voids shrinks, the gas pressure inside the voids increases and becomes higher than the external pressure. At this point, hydrogen diffusion into the compact is severely hindered; especially for large-sized compacts, the resistance to hydrogen flow is even greater. Under these conditions, unreduced oxides and internal oxygen within the voids react preferentially with tungsten / molybdenum atoms to form oxides, which remain inside the sintered body. This results in the inability to completely eliminate the 30-50 ppm oxygen content inside the sintered body, thus becoming one of the key factors affecting the performance of tungsten / molybdenum materials. Therefore, the combined effect of increased sintering temperature and shrinking void volume inside the compact causes the internal gas pressure to be greater than the external pressure, thereby hindering hydrogen diffusion and reduction. Therefore, even with continuously increasing temperature or extending the sintering time, the oxygen content in the sintered body cannot be fundamentally eliminated; this is why the final 30-50 ppm oxygen content in tungsten / molybdenum and its alloys cannot be eliminated.

[0011] Based on the analysis of the above deoxidation methods and results for tungsten / molybdenum sintered bodies, the existing deoxidation methods mainly have the following problems: 1. Incomplete deoxidation: High temperature and long time are key factors for deoxidation, but due to the continuous increase in internal pressure of the sintered body pores during the sintering process, hydrogen diffusion into the pores is severely hindered, resulting in the inability to further reduce the oxygen content; 2. High energy consumption and long time: The core value of the tungsten / molybdenum sintering process is densification, but due to the need for oxygen reduction, the heating rate is reduced and the sintering time is extended, which increases the time and energy consumption; 3. Difficulty in grain control: The grain size of sintered crystals is an important indicator for evaluating the quality of tungsten / molybdenum products. Short sintering time and low temperature help to form fine-grained structures, while conversely, coarse-grained structures are formed. Since deoxidation requires additional sintering time, it often results in coarse grains in the sintered body, affecting the later performance of the material; 4. Carbon reduction: It helps with deoxidation, but due to the appearance of brittle carbides, it affects the processing performance of the material and is often not suitable for widespread use.

[0012] The fundamental reason for the problems mentioned above in existing deoxidation methods is that during the sintering process, the original air in the sintered blank, along with the increase in temperature and the shrinkage of pore volume, creates an internal pressure in the sintered body that is mainly composed of air, which is greater than the external pressure that is mainly composed of hydrogen. This increases the internal oxidation process while hindering the diffusion and reduction of hydrogen inward. Summary of the Invention

[0013] The purpose of this invention is to provide a method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides. This method has a simple preparation process and high deoxidation efficiency. The product obtained by this method has significantly refined sintered crystal grains, thus improving the material properties.

[0014] To achieve the above objectives, the preparation method of the present invention includes the following steps:

[0015] Step 1: Thoroughly mix tungsten / molybdenum or its alloy powder with metal hydride at a ratio of 1%-10% of the total mass of tungsten / molybdenum or its alloy powder. Then, press the mixture into a compact. Place the compact into a sintering furnace, evacuate the furnace, and then heat the sintering furnace to perform vacuum degassing, thus completing the first removal of free oxygen and water vapor from the compact.

[0016] Step 2: After the first removal is completed, dry hydrogen is introduced into the sintering furnace. Under negative pressure, the hydrogen enters the gap of the compact and completes the second removal of oxygen inside the compact.

[0017] Step 3: After the second dehydrogenation is completed, the sintering furnace is heated in stages and held at the temperature to raise the temperature above the dehydrogenation temperature of the metal hydride, thus completing the third deep deoxidation of the hydride in situ. Finally, the furnace is cooled to obtain low-oxygen tungsten / molybdenum or its alloy.

[0018] In step one, the temperature for vacuum degassing is 200℃, and the time is 1-2 hours.

[0019] In step one, the metal hydride is one of titanium hydride, zirconium hydride, or rare earth hydride.

[0020] When the metal hydride is titanium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 300℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 500℃ at a heating rate of 20℃ / min and hold for 3 hours; then heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 790℃ at a heating rate of 10℃ / min and hold for 3 hours.

[0021] When the metal hydride is zirconium hydride, the specific steps of the stepped heating and holding in step three are as follows: First, heat to 300℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 450℃ at a heating rate of 20℃ / min and hold for 1 hour; next, heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 730℃ at a heating rate of 10℃ / min and hold for 3 hours; finally, heat to 1300℃ at a heating rate of 10℃ / min and hold for 1 hour.

[0022] The rare earth hydride is one of lanthanum hydride, yttrium hydride, or cerium hydride.

[0023] When the metal hydride is lanthanum hydride, the specific steps of the stepwise heating and holding in step three are as follows: first, heat to 850℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 920℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 990℃ at a heating rate of 10℃ / min and hold for 3 hours.

[0024] When the metal hydride is yttrium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 1500℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 1800℃ at a heating rate of 20℃ / min and hold for 1.5 hours; then heat to 2000℃ at a heating rate of 10℃ / min and hold for 3 hours; finally, heat to 2300℃ at a heating rate of 10℃ / min and hold for 1 hour.

[0025] When the metal hydride is cerium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 500℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 800℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 950℃ at a heating rate of 10℃ / min and hold for 1 hour.

[0026] The tungsten / molybdenum alloy prepared by the above method has a grain size of 15-30 μm and an internal oxygen content of 10-25 ppm.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention adopts an in-situ dehydrogenation and deoxygenation sintering process, which is simple in preparation process and saves costs.

[0029] (2) In this invention, the raw materials are mixed with hydrides, which together with the introduced hydrogen atmosphere form internal and external hydrogen for deoxygenation. The deoxygenation is thorough and efficient, while significantly shortening the sintering time and refining the sintered crystal grains.

[0030] (3) This invention utilizes the advantages of vacuum and hydrogen sintering to form a combined sintering, thereby improving material properties.

[0031] (4) The tungsten / molybdenum alloy prepared by the present invention has significantly reduced grain size and reduced internal oxygen content to 10-25 ppm, resulting in a significant improvement in material properties.

[0032] (5) The present invention has a wide range of applications and can also be applied to powder metallurgy and sintering of alloy materials. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1 provides a method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides. The specific steps are as follows:

[0035] Step 1: Tungsten / molybdenum powder or its alloy powder and titanium hydride are mechanically mixed at a titanium hydride addition amount of 1% of the total volume of tungsten / molybdenum or its alloy powder. Then, the mixture is pressed into a compact. After the compact is placed in a sintering furnace, the furnace is evacuated. The sintering furnace is then heated to 200°C for 2 hours for vacuum degassing to complete the first removal of free oxygen and water vapor from the compact.

[0036] Step 2: After the first removal is completed, the furnace cavity and the internal voids of the compact are under negative pressure. Dry hydrogen is introduced into the sintering furnace at a flow rate of 650 ml / min. Under the action of negative pressure, the hydrogen quickly and fully enters the voids of the compact, completing the second removal of oxygen from the interior of the compact.

[0037] Step 3: After the second deoxidation is completed, due to the stable pressure balance inside and outside the voids, the reduction of hydrogen and the re-oxidation of tungsten / molybdenum or its alloy powder by the newly generated water vapor gradually reach equilibrium. The furnace temperature is first raised to 300℃ at a rate of 20℃ / min and held for 2 hours, then raised to 500℃ at a rate of 20℃ / min and held for 3 hours, then raised to 600℃ at a rate of 20℃ / min and held for 2 hours, and finally raised to 790℃ at a rate of 10℃ / min and held for 3 hours. The hydrides inside the compact begin to undergo dehydrogenation, releasing high-purity hydrogen gas, which begins in-situ deoxidation inside the compact. As the temperature rises, sintering necks form inside the compact, the voids shrink, and the internal pressure increases. At this time, it is difficult for hydrogen gas outside the voids to diffuse inward, and the dehydrogenation of hydrides becomes the main source of reducing agent inside the voids, further maintaining the internal reducing atmosphere and reducing state, completing the third deep deoxidation. Finally, the furnace is cooled to obtain tungsten / molybdenum or its alloy.

[0038] Titanium hydride is used because TiH2 decomposes slowly at 400℃ and undergoes complete dehydrogenation at 600-800℃; it has high chemical stability, does not react with air or water, but readily reacts with strong oxidants, and can serve as a source of high-purity hydrogen. TiH2 undergoes rapid dehydrogenation at around 500℃, and the oxidation temperature of Ti is also around 500℃, with the oxidation rate reaching its maximum at 800℃. The decomposition temperature of TiO2 is between 800-1000℃; therefore, to preserve the TiO2 second phase, the sintering temperature must not exceed 800℃.

[0039] Example 2 provides a method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides. The specific steps are as follows:

[0040] Step 1: Tungsten / molybdenum powder or its alloy powder is mechanically mixed with zirconium hydride at a ratio of 10% of the total volume of tungsten / molybdenum or its alloy powder. The mixture is then pressed into a compact. The compact is placed in a sintering furnace, and the furnace is evacuated. The furnace is then heated to 200°C for 1 hour of vacuum degassing to complete the first removal of free oxygen and water vapor from the compact.

[0041] Step 2: After the first removal is completed, the furnace cavity and the internal voids of the compact are under negative pressure. Dry hydrogen is introduced into the sintering furnace at a flow rate of 650 ml / min. Under the action of negative pressure, the hydrogen quickly and fully enters the voids of the compact, completing the second removal of oxygen from the interior of the compact.

[0042] Step 3: After the second removal is completed, due to the stable pressure balance inside and outside the pores, the reduction of hydrogen and the re-oxidation of tungsten / molybdenum or its alloy powder by the newly generated water vapor gradually reach equilibrium. The furnace temperature is first increased to 300℃ at a rate of 20℃ / min and held for 2 hours, then increased to 450℃ at a rate of 20℃ / min and held for 1 hour, then increased to 600℃ at a rate of 20℃ / min and held for 2 hours, and finally increased to 730℃ at a rate of 10℃ / min and held for 3 hours. Finally, the temperature is increased to 1300℃ at a heating rate of 10℃ / min and held for 1 hour. The hydrides inside the compact begin to undergo dehydrogenation, releasing high-purity hydrogen gas to begin in-situ deoxidation inside the compact. As the temperature rises, sintering necks form inside the compact, the voids shrink, and the internal pressure increases. At this time, it is difficult for hydrogen gas outside the voids to diffuse inward. Hydride dehydrogenation becomes the main source of reducing agent in the voids, further maintaining the internal reducing atmosphere and reducing state, completing the third deep deoxidation. Finally, the product is obtained by furnace cooling.

[0043] Zirconium hydride is used because ZrH2 oxidation is not obvious below 400℃, but significant oxidation and weight gain occur above 450℃. ZrH2 undergoes vigorous dehydrogenation at around 730℃, and ZrO2 has a very high decomposition temperature (ZrO2 fibers can still be used at 1500℃). ZrO2 forms low-valence oxides when heated with H2 (reaction temperature above 1000℃).

[0044] Example 3 provides a method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides. The specific steps are as follows:

[0045] Step 1: Tungsten / molybdenum powder or its alloy powder is mechanically mixed with lanthanum hydride at a ratio of 5% of the total volume of tungsten / molybdenum or its alloy powder. The mixture is then pressed into a compact. The compact is placed in a sintering furnace, and the furnace is evacuated. The furnace is then heated to 200°C for 1.5 hours of vacuum degassing to complete the first removal of free oxygen and water vapor from the compact.

[0046] Step 2: After the first removal is completed, the furnace cavity and the internal voids of the compact are under negative pressure. Dry hydrogen is introduced into the sintering furnace at a flow rate of 650 ml / min. Under the action of negative pressure, the hydrogen quickly and fully enters the voids of the compact, completing the second removal of oxygen from the interior of the compact.

[0047] Step 3: After the second deoxidation is completed, due to the stable pressure balance inside and outside the voids, the reduction of hydrogen and the re-oxidation of tungsten / molybdenum or its alloy powder by the newly generated water vapor gradually reach equilibrium. The furnace temperature is first raised to 850℃ at a rate of 20℃ / min and held for 2 hours, then raised to 920℃ at a rate of 20℃ / min and held for 2 hours, and finally raised to 990℃ at a rate of 10℃ / min and held for 3 hours. The hydrides inside the compact begin to undergo dehydrogenation, releasing high-purity hydrogen gas, which begins in-situ deoxidation inside the compact. As the temperature rises, sintering necks form inside the compact, the voids shrink, and the internal pressure increases. At this time, it is difficult for hydrogen gas outside the voids to diffuse inward, and the dehydrogenation of hydrides becomes the main source of reducing agent inside the voids, further maintaining the internal reducing atmosphere and reducing state, completing the third deep deoxidation. Finally, the finished product is obtained by cooling in the furnace.

[0048] While using rare earth hydrides for internal and external deoxidation, the corresponding oxides produced can significantly improve the strength and toughness of the material. When using lanthanum hydride, since lanthanum hydride will gradually release hydrogen and generate lanthanum oxide when the temperature exceeds 850℃, and the decomposition temperature of lanthanum oxide is above 1000℃, the heating temperature should not exceed 1000℃.

[0049] Example 4 provides a method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides. The specific steps are as follows:

[0050] Step 1: Tungsten / molybdenum powder or its alloy powder is mechanically mixed with yttrium hydride at a ratio of 3% of the total volume of tungsten / molybdenum or its alloy powder. The mixture is then pressed into a compact. The compact is placed in a sintering furnace, and the furnace is evacuated. The furnace is then heated to 200°C for 1 hour for vacuum degassing to complete the first removal of free oxygen and water vapor from the compact.

[0051] Step 2: After the first removal is completed, the furnace cavity and the internal voids of the compact are under negative pressure. Dry hydrogen is introduced into the sintering furnace at a flow rate of 650 ml / min. Under the action of negative pressure, the hydrogen quickly and fully enters the voids of the compact, completing the second removal of oxygen from the interior of the compact.

[0052] Step 3: After the second deoxidation is completed, due to the stable pressure balance inside and outside the voids, the reduction of hydrogen and the re-oxidation of tungsten / molybdenum or its alloy powder by the newly generated water vapor gradually reach equilibrium. The furnace temperature is first raised to 1500℃ at a rate of 20℃ / min and held for 2 hours, then raised to 1800℃ at a rate of 20℃ / min and held for 1.5 hours, then raised to 2000℃ at a rate of 10℃ / min and held for 3 hours, and finally raised to 2300℃ at a rate of 10℃ / min and held for 1 hour. The hydrides inside the compact begin to undergo dehydrogenation, releasing high-purity hydrogen gas, which begins in-situ deoxidation inside the compact. As the temperature rises, sintering necks form inside the compact, the voids shrink, and the internal pressure increases. At this time, it is difficult for hydrogen gas outside the voids to diffuse inward, and the dehydrogenation of hydrides becomes the main source of reducing agent inside the voids, further maintaining the internal reducing atmosphere and reducing state, completing the third deep deoxidation. Finally, the finished product is obtained by cooling in the furnace.

[0053] While using rare earth hydrides for internal and external deoxidation, the corresponding oxides produced can significantly improve the strength and toughness of the material. When using yttrium hydride, it will gradually release hydrogen and generate yttrium oxide when the temperature of yttrium hydride exceeds 1465℃. The decomposition temperature of yttrium oxide is above 2400℃, so the heating temperature should not exceed 2400℃.

[0054] Example 5 provides a method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides. The specific steps are as follows:

[0055] Step 1: Tungsten / molybdenum powder or its alloy powder is mechanically mixed with cerium hydride at a ratio of 8% of the total volume of tungsten / molybdenum or its alloy powder. The mixture is then pressed into a compact. The compact is placed in a sintering furnace, and the furnace is evacuated. The furnace is then heated to 200°C for 2 hours for vacuum degassing to complete the first removal of free oxygen and water vapor from the compact.

[0056] Step 2: After the first removal is completed, the furnace cavity and the internal voids of the compact are under negative pressure. Dry hydrogen is introduced into the sintering furnace at a flow rate of 650 ml / min. Under the action of negative pressure, the hydrogen quickly and fully enters the voids of the compact, completing the second removal of oxygen from the interior of the compact.

[0057] Step 3: After the second deoxidation is completed, due to the stable pressure balance inside and outside the voids, the reduction of hydrogen and the re-oxidation of tungsten / molybdenum or its alloy powder by the newly generated water vapor gradually reach equilibrium. The furnace temperature is first raised to 500℃ at a rate of 20℃ / min and held for 2 hours, then raised to 600℃ at a rate of 20℃ / min and held for 2 hours, then raised to 800℃ at a rate of 20℃ / min and held for 2 hours, and finally raised to 950℃ at a rate of 10℃ / min and held for 1 hour. The hydrides inside the compact begin to undergo dehydrogenation, releasing high-purity hydrogen gas, which begins in-situ deoxidation inside the compact. As the temperature rises, sintering necks form inside the compact, the voids shrink, and the internal pressure increases. At this time, it is difficult for hydrogen gas outside the voids to diffuse inward, and the dehydrogenation of hydrides becomes the main source of reducing agent inside the voids, further maintaining the internal reducing atmosphere and reducing state, completing the third deep deoxidation. Finally, the finished product is obtained by cooling in the furnace.

[0058] While using rare earth hydrides for internal and external deoxidation, the corresponding oxides produced can significantly improve the strength and toughness of the material. When using cerium hydride at temperatures exceeding 500°C, cerium hydride will gradually release hydrogen and generate cerium oxide. The decomposition temperature of cerium oxide is above 1000°C, so the heating temperature should not exceed 1000°C.

[0059] Experimental section:

[0060] To address the problems of traditional deoxidation methods for tungsten / molybdenum and their alloys, and through analysis of the sintering process, it was determined that the increased internal gas pressure in the compact's voids due to the combined effects of temperature and shrinkage severely hinders the diffusion of external hydrogen, leading to incomplete deoxidation. Metal hydrides, as hydrogen storage materials, contain a certain amount of high-purity hydrogen dissolved within them. At high temperatures, these metal hydrides undergo a dehydrogenation reaction, releasing hydrogen gas. This allows for in-situ reduction of oxides within the compact, effectively overcoming the problem of external hydrogen being unable to enter due to excessive internal pressure. Furthermore, it effectively avoids the negative consequences of brittle carbides formed during deoxidation via carbon addition. The dehydrogenated metal element possesses high chemical reactivity. After releasing hydrogen gas to reduce surrounding oxides, it further combines with remaining free oxygen atoms to form new metal oxides. These newly formed metal oxides can act as second-phase particles within the sintered body, pinning the grain boundaries of tungsten / molybdenum and their alloys, refining grain size, and improving material properties. Thus, the core of this invention is to combine the internal hydrogen generated by the dehydrogenation reaction of metal hydrides with the hydrogen in the furnace cavity outside the sintering body to form a deep deoxidation process with hydrogen inside and outside the pressed billet.

[0061] The finished product prepared by this invention has significantly refined sintered crystal grains due to the reduced sintering time, and the internal oxygen content of the finished product is lower than 30-50 ppm. Due to the lower oxygen content, the material properties are further improved.

Claims

1. A method for preparing tungsten / molybdenum alloys through in-situ dehydrogenation and deep deoxidation of hydrides, characterized in that, Includes the following steps: Step 1: Thoroughly mix tungsten / molybdenum or its alloy powder with metal hydride at a ratio of 1%-10% of the total mass of tungsten / molybdenum or its alloy powder. Then, press the mixture into a compact. Place the compact into a sintering furnace, evacuate the furnace, and then heat the sintering furnace to perform vacuum degassing, thus completing the first removal of free oxygen and water vapor from the compact. The metal hydride is one of titanium hydride, zirconium hydride, or rare earth hydride. Step 2: After the first removal is completed, dry hydrogen is introduced into the sintering furnace. Under negative pressure, the hydrogen enters the gap of the compact and completes the second removal of oxygen inside the compact. Step 3: After the second dehydrogenation is completed, the sintering furnace is heated in stages and held at that temperature until it exceeds the dehydrogenation temperature of the metal hydride. This completes the third deep deoxidation of the hydride in situ. Finally, the furnace is cooled to obtain low-oxygen tungsten / molybdenum or its alloy. After the dehydrogenated metal element reduces the surrounding oxides with the released hydrogen gas, it further combines with the remaining free oxygen atoms to form new metal oxides as the second phase particles in the sintered body. This process pins the grain boundaries of tungsten / molybdenum and its alloys, refines the grain size, and improves the material properties.

2. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 1, characterized in that: In step one, the temperature for vacuum degassing is 200℃, and the time is 1-2 hours.

3. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 1, characterized in that: When the metal hydride is titanium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 300℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 500℃ at a heating rate of 20℃ / min and hold for 3 hours; then heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 790℃ at a heating rate of 10℃ / min and hold for 3 hours.

4. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 1, characterized in that: When the metal hydride is zirconium hydride, the specific steps of the stepped heating and holding in step three are as follows: First, heat to 300℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 450℃ at a heating rate of 20℃ / min and hold for 1 hour; next, heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 730℃ at a heating rate of 10℃ / min and hold for 3 hours; finally, heat to 1300℃ at a heating rate of 10℃ / min and hold for 1 hour.

5. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 2, characterized in that: The rare earth hydride is one of lanthanum hydride, yttrium hydride, or cerium hydride.

6. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 5, characterized in that: When the metal hydride is lanthanum hydride, the specific steps of the stepwise heating and holding in step three are as follows: first, heat to 850℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 920℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 990℃ at a heating rate of 10℃ / min and hold for 3 hours.

7. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 5, characterized in that: When the metal hydride is yttrium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 1500℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 1800℃ at a heating rate of 20℃ / min and hold for 1.5 hours; then heat to 2000℃ at a heating rate of 10℃ / min and hold for 3 hours; finally, heat to 2300℃ at a heating rate of 10℃ / min and hold for 1 hour.

8. The method for preparing tungsten / molybdenum alloys by in-situ dehydrogenation and deep deoxidation of hydrides as described in claim 5, characterized in that: When the metal hydride is cerium hydride, the specific steps of the stepped heating and holding in step three are as follows: first, heat to 500℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 600℃ at a heating rate of 20℃ / min and hold for 2 hours; then heat to 800℃ at a heating rate of 20℃ / min and hold for 2 hours; finally, heat to 950℃ at a heating rate of 10℃ / min and hold for 1 hour.

9. A tungsten / molybdenum alloy obtained by the method for preparing tungsten / molybdenum alloy by in-situ dehydrogenation and deep deoxidation of hydrides as described in any one of claims 1-8, characterized in that, The tungsten / molybdenum alloy has a grain size of 15-30 μm and an internal oxygen content of 10-25 ppm.