A molybdenum alloy and a method of making the same

Abstract

This invention relates to a molybdenum alloy and its preparation method, belonging to the field of powder metallurgy nanostructure materials technology. The main technical solution adopted is as follows: the molybdenum alloy comprises the following chemical composition by mass percentage: C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, with the balance being Mo. This invention controls the size and distribution of the second phase through compositional design, introducing coherent / semi-coherent rare earth composite oxides that form coherent / semi-coherent structures with the matrix to achieve grain refinement and grain boundary purification. Based on the above, this invention introduces ZrC, at least a portion of which can form ZrO2 during sintering, thereby further reducing the oxygen content of the alloy matrix and increasing the grain boundary bonding strength, thus further improving the strength and plasticity of the alloy.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy nanostructure materials technology, and in particular to a molybdenum alloy and its preparation method. Background Technology

[0002] Molybdenum, a refractory metal with a high melting point (2623℃), excellent high-temperature strength, good thermal and electrical conductivity, and a low coefficient of thermal expansion, has irreplaceable application value in high-end fields such as aerospace, electronics, and high-temperature metallurgy. For example, in the aerospace field, molybdenum alloys can be used to manufacture thermal protection components for engine thrust chambers; in the electronics field, molybdenum alloys are often used as lead frames for large-scale integrated circuits and heat dissipation components for radio frequency devices. As these high-end industries rapidly develop towards higher parameters, longer lifespans, and higher reliability, more stringent requirements are being placed on the comprehensive performance of molybdenum alloys. They not only need to maintain stable mechanical properties under extreme high-temperature environments (above 1200℃), but also need to possess good room-temperature plasticity, high-temperature oxidation resistance, and processing and forming properties.

[0003] However, pure molybdenum and traditional molybdenum alloys have significant performance shortcomings in practical applications, hindering their further promotion in high-end fields. On the one hand, pure molybdenum has high room temperature brittleness and insufficient high-temperature strength, making it prone to fracture failure under external impact or long-term high-temperature service. To improve this problem, traditional methods often involve adding elements such as titanium, zirconium, hafnium, and carbon to form molybdenum alloys (such as TZM molybdenum alloys and Mo-Hf-C alloys). Although this can improve high-temperature strength to some extent, the high-temperature oxidation resistance of these alloys is still poor. In oxidizing atmospheres above 600°C, they easily form loose and porous molybdenum oxide (MoO3) rapidly, leading to surface peeling and a sharp decline in performance. Additional coating protection (such as aluminide coatings and silicide coatings) is required, which not only increases the preparation cost but also poses the risk of poor adhesion between the coating and the substrate and coating failure after long-term service. On the other hand, the preparation process of traditional molybdenum alloys also faces technical bottlenecks. Currently, the mainstream industrial method for preparing molybdenum alloys is the "powder metallurgy + plastic processing" process. This involves first pressing molybdenum powder and alloying element powder into a billet using cold isostatic pressing, then sintering at high temperatures (typically 1800-2200℃) to obtain a dense billet, and finally processing it into a finished product through forging, rolling, and other plastic processing methods. However, this process has the following problems: First, abnormal grain growth is prone to occur during high-temperature sintering, leading to a further reduction in the material's room-temperature plasticity; second, for complex-shaped components, plastic processing is difficult and yields low, making it difficult to meet the demands of high-end equipment for irregularly shaped components; third, the preparation process is energy-intensive and time-consuming, which does not align with the current trend of green manufacturing.

[0004] In summary, there is an urgent need to develop a new type of molybdenum alloy and its preparation method that combines high strength, high plasticity, simple preparation process, and controllable cost. Summary of the Invention

[0005] In view of this, the present invention provides a molybdenum alloy and a method for preparing the same, with the main objective of providing a high-strength, high-ductility molybdenum alloy.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] On one hand, embodiments of the present invention provide a molybdenum alloy, wherein, by mass percentage, the molybdenum alloy comprises the following chemical components:

[0008] C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, balance Mo;

[0009] The microstructure of the molybdenum alloy comprises a molybdenum matrix of BCC and nano-reinforcing phases; wherein the nano-reinforcing phases include nano-Y₂O₃, nano-ZrO₂, nano-ZrC, and nano-Y x Zr y O (1.5x+2y) A mixed phase; wherein the nano-reinforced phase and the molybdenum matrix are coherent or semi-coherent; wherein x is 0.1-5.

[0010] Preferably, the nano-reinforced phase is spherical with a size of 10nm-200nm.

[0011] Preferably, the strengthening methods of the molybdenum alloy include nanophase dispersion strengthening and solid solution strengthening of tungsten.

[0012] Preferably, the molybdenum alloy has a tensile strength greater than 600 MPa and an elongation at break greater than 27% at room temperature.

[0013] Preferably, the method for preparing the molybdenum alloy includes the following steps:

[0014] Step 1): Add ammonium molybdate, ammonium tungstate, and rare earth yttrium salt to water, and heat and stir to promote dissolution, to obtain the precursor liquid;

[0015] Step 2): The precursor liquid is heated to form a complex precursor; the complex precursor is dried to obtain a mixed powder.

[0016] Step 3): The mixed powder is calcined to obtain doped molybdenum oxide powder;

[0017] Step 4): The doped molybdenum oxide powder is reduced under a hydrogen atmosphere to obtain molybdenum powder; wherein the molybdenum powder is doped with rare earth elements and W elements;

[0018] Step 5): The molybdenum powder and nano-zirconium carbide are ball-milled to obtain molybdenum powder doped with nano-zirconium carbide;

[0019] Step 6): The molybdenum powder doped with nano-zirconium carbide is sintered to obtain a molybdenum alloy.

[0020] Preferably, the ammonium molybdate is one or more of ammonium dimolybdate, ammonium tetramolybdate, and ammonium heptamolybdate; the ammonium tungstate is one or two of ammonium paratungstate and ammonium metatungstate; and the rare earth yttrium salt is selected from yttrium acetate and / or yttrium nitrate.

[0021] Preferably, in step 1), the temperature of the heating and stirring treatment is 60℃-80℃, the rotation speed of the heating and stirring treatment is greater than 80 revolutions per minute, and the duration of the heating and stirring treatment is greater than 30 minutes.

[0022] Preferably, in step 2), citric acid is added to the precursor liquid to adjust the pH value of the liquid to 1-3, making the solution clear, and then heated to form a complex precursor.

[0023] Preferably, in step 2), the temperature of the heat treatment is 65℃-85℃.

[0024] Preferably, in step 2), the drying process is selected from vacuum drying, spray drying, and freeze drying.

[0025] Preferably, in step 3), the roasting atmosphere is atmospheric, the roasting temperature is 450℃-650℃, and the roasting time is 2h-4h.

[0026] Preferably, in step 4):

[0027] Under a hydrogen reducing atmosphere, the doped molybdenum oxide powder is heated to 550℃-650℃ and held for 2-4 hours, and then heated to 700℃-950℃ and held for 2-8 hours to carry out reduction treatment to obtain molybdenum powder; wherein, during the reduction treatment, the thickness of the doped molybdenum oxide powder is 3mm-5mm.

[0028] Preferably, in step 4), the particle size of the molybdenum powder is 300nm-2000nm.

[0029] Preferably, in step 5), the particle size of the nano-zirconium carbide is 10nm-150nm.

[0030] Preferably, in step 5), the molybdenum powder has a core-shell structure with rare earth oxides as the core and elemental molybdenum layers as the shell; wherein, W element is dissolved in elemental molybdenum layers.

[0031] Preferably, in step 6): the molybdenum powder doped with nano-zirconium carbide is heated to 1000℃-1100℃ for sintering for 1h-2.5h, then heated to 1150℃-1350℃ for sintering for 2-4h, then heated to 1400℃-1600℃ for sintering for 2-4h, and finally heated to 2000℃-2200℃ for sintering for 4-8h to obtain a molybdenum alloy, wherein the sintering pressure is 40-80MPa.

[0032] Compared with the prior art, the molybdenum alloy and its preparation method of the present invention have at least the following beneficial effects:

[0033] On one hand, embodiments of the present invention provide a molybdenum alloy, comprising the following chemical composition by mass percentage: C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, with the balance being Mo. Here, the present invention, through compositional design, controls the size and distribution of the second phase, introducing coherent / semi-coherent rare earth composite oxides that form with the matrix, simultaneously achieving grain refinement and grain boundary purification, successfully preparing a high-strength and high-toughness composite-strength molybdenum alloy with composite strengthening effect. Based on the above, the present invention introduces ZrC, a portion of which can form ZrO2 during sintering, thereby further reducing the oxygen content of the alloy matrix and increasing grain boundary bonding strength, thus further improving the strength and plasticity of the alloy; another portion of zirconium carbide provides dispersion strengthening. In summary, the aforementioned alloy addresses the mismatch between strength and toughness in molybdenum alloys, as well as the anisotropy problem in plates / bars, and is expected to solve the welding cracking problem caused by anisotropy. Furthermore, it should be noted that the chemical composition design of this invention, matched with a liquid-liquid mixing process, allows yttrium and molybdenum to achieve molecular-level mixing in the solution. The ball milling process used when introducing zirconium carbide further enhances the uniform distribution of yttrium oxide. Because yttrium oxide and zirconium carbide are small and have the same crystal structure as the matrix, they form a coherent / semi-coherent structure. During sintering, the fine and dispersed distribution of the second phase can hinder grain boundary expansion and grain growth, thus achieving grain refinement. After grain refinement, the grain boundary area per unit volume increases, which can reduce the oxygen content at the grain boundaries per unit area, effectively purifying the grain boundaries.

[0034] Furthermore, embodiments of the present invention provide a molybdenum alloy, wherein the microstructure of the molybdenum alloy comprises a molybdenum matrix of BCC and a nano-reinforcing phase; wherein the nano-reinforcing phase comprises nano-Y₂O₃, nano-ZrO₂, nano-ZrC, and nano-Y x Zr y O (1.5x+2y)The mixture comprises a nano-reinforcing phase that is coherent or semi-coherent with the molybdenum matrix. The nano-reinforcing phase is spherical with a size of 10 nm-200 nm, providing dispersion reinforcement and toughening through the Orovan mechanism during plastic deformation.

[0035] On the other hand, embodiments of the present invention provide a method for preparing a molybdenum alloy, wherein the method includes the following steps: adding ammonium molybdate, ammonium tungstate, and rare earth yttrium salt to water, heating and stirring to promote dissolution, to obtain a precursor liquid; heating the precursor liquid to form a complex precursor; drying the complex precursor to obtain a mixed powder; calcining the mixed powder to obtain doped molybdenum oxide powder; reducing the doped molybdenum oxide powder under a hydrogen atmosphere to obtain molybdenum powder; wherein the molybdenum powder is doped with rare earth elements and W; ball milling the molybdenum powder and nano-zirconium carbide to obtain molybdenum powder doped with nano-zirconium carbide; sintering the molybdenum powder doped with nano-zirconium carbide to obtain a molybdenum alloy. The above preparation method is explained as follows: the present invention simplifies the process flow, eliminating the need for forging to obtain a high-strength and high-toughness molybdenum alloy with a room temperature strength higher than 600 MPa and an elongation higher than 27%, significantly reducing production costs and energy consumption, and conforming to green manufacturing. Using rare earth acetate can effectively reduce the emission of harmful gases and significantly lower the environmental protection costs of enterprises during production. This invention uses ammonium molybdate, ammonium tungstate, rare earth salts, and nano-ZrC as raw materials. While reducing production costs, it obtains ultrafine molybdenum powder with low oxygen content, high dispersion, and high porosity through multi-temperature reduction treatment. During the reduction process, molybdenum powder continuously deposits on the surface using nano-rare earth oxide particles as nucleation sites, forming a core-shell structure of rare earth oxide particles and ultrafine molybdenum powder. This ensures that the reinforcing phase is uniformly distributed within the grains during sintering. It is particularly important to note that the ZrC raw material in this application is introduced after the reduction treatment step. After ball milling with molybdenum powder, the final sintering yields a molybdenum alloy. This treatment avoids premature addition of zirconium carbide, which would lead to re-calcination and oxidation by oxygen during reduction, thus reducing the deoxidation effect during sintering. Furthermore, adding ZrC through ball milling after reduction treatment maximizes the retention of zirconium carbide, and ball milling further ensures a more uniform and fine distribution of the second phase.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Attached Figure Description

[0037] Figure 1 This is a microstructure diagram of the molybdenum alloy prepared in Example 1;

[0038] Figure 2 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 1;

[0039] Figure 3 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 2;

[0040] Figure 4 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 3;

[0041] Figure 5 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 4;

[0042] Figure 6 These are mechanical property diagrams of the molybdenum alloys prepared in Example 1 and Comparative Examples 1-4. Detailed Implementation

[0043] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0044] This invention aims to systematically overcome these bottlenecks through compositional innovation and process optimization, thereby enhancing my country's independent innovation capabilities in the field of high-performance refractory metal materials. This invention designs a novel ODS molybdenum alloy that combines dispersion strengthening and solid solution strengthening effects through optimized compositional design. By controlling the size and distribution of the second phase and introducing coherent / semi-coherent rare earth composite oxides to form with the matrix, the invention simultaneously achieves grain refinement and grain boundary purification, resulting in a good match between room-temperature strength and ductility of the molybdenum alloy and improved weldability, making it highly valuable for engineering applications. The main components of this invention are as follows:

[0045] On one hand, embodiments of the present invention provide a molybdenum alloy, wherein, by mass percentage, the molybdenum alloy comprises the following chemical composition: C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, with the balance being Mo.

[0046] Regarding the above-mentioned scheme, the following explanation is necessary: ​​This invention, through compositional design and control of the size and distribution of the second phase, introduces rare-earth composite oxides that form coherent / semi-coherent structures with the matrix, simultaneously refining grains and purifying grain boundaries. This successfully prepares a high-strength, high-toughness composite-strength reinforced molybdenum alloy with composite strengthening effect. Building upon this, the invention introduces ZrC, some of which can form ZrO2 during sintering, further reducing the oxygen content of the alloy matrix and increasing grain boundary bonding strength, thereby further improving the alloy's strength and plasticity. In summary, this alloy solves the strength-toughness mismatch problem of molybdenum alloys and the anisotropy problem in plates / bars, and is expected to solve the welding cracking problem caused by anisotropy.

[0047] Preferably, the microstructure of the molybdenum alloy comprises a molybdenum matrix of BCC and a nano-reinforcing phase; wherein the nano-reinforcing phase comprises nano-Y₂O₃, nano-ZrO₂, nano-ZrC, and nano-Y x Zr y O (1.5x+2y) A mixed phase; wherein the nano-reinforced phase and the molybdenum matrix have a coherent or semi-coherent structure.

[0048] Preferably, the strengthening methods of the molybdenum alloy described above in the embodiments of the present invention include nanophase dispersion strengthening and tungsten solid solution strengthening.

[0049] Preferably, the molybdenum alloy described above in the embodiments of the present invention has a tensile strength greater than 600 MPa and an elongation at break greater than 27% at room temperature.

[0050] On the other hand, embodiments of the present invention provide a method for preparing the molybdenum alloy according to any of the above claims, wherein the method for preparing the molybdenum alloy includes the following steps:

[0051] Step 1): Add ammonium molybdate, ammonium tungstate, and rare earth yttrium salt to water, heat and stir to promote dissolution, and obtain the precursor liquid.

[0052] The ammonium molybdate is one or more of ammonium dimolybdate, ammonium tetramolybdate, and ammonium heptamolybdate. The ammonium tungstate is one or two of ammonium paratungstate and ammonium metatungstate. It should be noted that either anhydrous ammonium molybdate or ammonium molybdate containing water of crystallization can be used as the ammonium molybdate. Similarly, either anhydrous ammonium tungstate or ammonium tungstate containing water of crystallization can be used as the ammonium tungstate.

[0053] In this step, ammonium molybdate, ammonium tungstate, and yttrium acetate / yttrium nitrate (anhydrous yttrium acetate / yttrium nitrate or yttrium acetate / yttrium nitrate containing water of crystallization can be used) are added to deionized water in a certain proportion, and a precursor liquid is obtained by heating and with the assistance of a magnetic stirrer. The heating method is constant temperature water bath heating at 60℃-80℃ (preferably 65℃); the magnetic stirring speed is greater than 80 revolutions per minute, and the duration is greater than 30 minutes.

[0054] Step 2): The precursor liquid is heated to form a complex precursor; the complex precursor is dried to obtain a mixed powder.

[0055] In this step, the precursor liquid is filtered to remove impurities, and citric acid is added to adjust the pH value of the liquid to 1-3 to clarify the solution. The solution is then heated to form a complex precursor, and dried to obtain a mixed powder. The heating method is a constant temperature water bath heating at 65℃-85℃ (preferably 80℃); the drying method is vacuum drying, spray drying, or freeze drying; and the mixed powder is a mixture of rare earth molybdenum salts.

[0056] Step 3): The mixed powder is calcined to obtain doped molybdenum oxide powder.

[0057] The mixed powder is placed in a muffle furnace (atmospheric atmosphere) and calcined to obtain doped molybdenum oxide powder; the calcination temperature is 450℃-650℃ and the calcination time is 2h-4h.

[0058] Step 4): The doped molybdenum oxide powder is reduced under a hydrogen atmosphere to obtain molybdenum powder; wherein the molybdenum powder is doped with rare earth elements and W elements.

[0059] In this process, under a hydrogen reducing atmosphere, the doped molybdenum oxide powder is heated to 550℃-650℃ and held for 2-4 hours, then heated to 700℃-950℃ and held for 2-8 hours for reduction treatment to obtain molybdenum powder. During the reduction treatment, the thickness of the doped molybdenum oxide powder is 3mm-5mm. The ultrafine molybdenum powder has a particle size of 300nm-2000nm.

[0060] Step 5): The molybdenum powder and nano-zirconium carbide are ball-milled to obtain molybdenum powder doped with nano-zirconium carbide.

[0061] The nano-zirconium carbide particles have a size of 10nm-150nm;

[0062] In this process, nano-zirconium carbide and ultrafine molybdenum powder are ball-milled and mixed at a speed of 240 r / min to obtain mixed ultrafine molybdenum powder. The molybdenum powder has a core-shell structure with rare earth oxides as the core and elemental molybdenum layers as the shell; wherein, W element is dissolved in the elemental molybdenum layers.

[0063] Step 6): The molybdenum powder doped with nano-zirconium carbide is sintered to obtain a molybdenum alloy.

[0064] The process involves heating the molybdenum powder doped with nano-zirconium carbide to 1000℃-1100℃ for sintering for 1h-2.5h, then raising the temperature to 1150℃-1350℃ for sintering for 2h-4h, followed by raising the temperature to 1400℃-1600℃ for sintering for 2-4h, and finally raising the temperature to 2000℃-2200℃ for sintering for 4-8h to obtain a molybdenum alloy. The sintering pressure is 40-80MPa.

[0065] In the above steps, the amount of each raw material used should be such that the final molybdenum alloy composition meets the following requirements:

[0066] C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, balance Mo.

[0067] The preparation process of the present invention is described below:

[0068] 1): This invention uses ammonium molybdate, ammonium tungstate, rare earth yttrium salts, and zirconium carbide as raw materials to obtain a low-cost, high-strength and high-toughness molybdenum alloy while shortening the production process and reducing production costs.

[0069] First, this invention dissolves the raw materials in deionized water, allowing rare earth elements and molybdenum elements to mix at the molecular scale in the liquid. After drying, a mixed precursor is obtained. Then, the mixture undergoes multi-temperature hydrogen reduction treatment, aiming to generate in-situ nano-rare earth oxide particles as the final alloy reinforcing phase during the powder reduction process. This ensures that the rare earth nanoparticles and molybdenum powder are evenly distributed, laying the foundation for obtaining a good dispersion strengthening effect. In addition, these rare earth nano-oxide particles can serve as nucleation sites for molybdenum powder, thereby obtaining nano-ultrafine molybdenum powder. Finally, high-temperature sintering is used in conjunction with the pinning effect of the nano-rare earth particles on the grain boundaries to obtain a high-strength and high-toughness molybdenum alloy with low grain size and high density, overcoming the problem of poor room temperature ductility of traditional sintered molybdenum alloys.

[0070] Among these, nanoparticles are beneficial for enhancing the activity of powders during sintering, thereby increasing the densification diffusion process during powder sintering. Furthermore, nano-rare earth particles can hinder grain boundary migration during high-temperature sintering, thus ensuring that the grains can maintain a fine-grained structure during high-temperature sintering, reducing the oxygen content per unit grain boundary area, weakening the grain boundary brittleness caused by oxygen segregation at the grain boundaries, increasing the grain boundary bonding strength, and thus significantly improving the overall performance of the material.

[0071] 2) This invention simplifies the process, eliminating the need for forging to obtain a high-strength, high-toughness molybdenum alloy with a room temperature strength exceeding 600 MPa and an elongation exceeding 30%, significantly reducing production costs and energy consumption, and conforming to green manufacturing principles. The use of rare earth acetate effectively reduces the emission of harmful gases, greatly lowering the environmental costs in the production process.

[0072] 3) This invention uses ammonium molybdate, ammonium tungstate, rare earth salts, and nano-ZrC as raw materials. While reducing production costs, it employs multi-temperature reduction treatment to obtain ultrafine molybdenum powder with low oxygen content, high dispersion, and high porosity. During the reduction process, molybdenum powder continuously deposits on the surface using nano-rare earth oxide particles as nucleation sites, thus forming a core-shell structure of rare earth oxide particles and ultrafine molybdenum powder. This ensures that the reinforcing phase is uniformly distributed within the grains during sintering.

[0073] 4): Drying the precursor liquid by spray drying or freeze drying can avoid the segregation of rare earth elements, thereby making it evenly distributed and forming a good dispersion enhancement effect.

[0074] The following specific examples further illustrate this point:

[0075] Example 1

[0076] This embodiment provides a method for preparing a molybdenum alloy, including the following steps:

[0077] Step 1): With the aid of a water bath and a magnetic stirrer, 14.2g of anhydrous yttrium tetraacetate, 3.6g of anhydrous ammonium tungstate, and 1820g of anhydrous ammonium molybdate were dissolved in deionized water to obtain a homogeneous and clear solution, i.e., the precursor liquid. The water bath temperature was 65℃, the magnetic stirrer speed was 120 rpm, and the stirring time was 120 minutes.

[0078] Step 2): Add citric acid to the precursor liquid to adjust the pH to 1, then heat in a water bath to 80°C to form a complex precursor. After that, spray dry to obtain a dry mixed powder.

[0079] Step 3) The dried mixed powder is calcined in a muffle furnace; the calcination temperature is 450℃ and the calcination time is 2h to obtain doped molybdenum oxide powder.

[0080] Step 4): The doped molybdenum oxide powder is placed in a hydrogen furnace, heated to 550℃ and held for 2 hours, then heated to 800℃ and held for 4 hours to obtain ultrafine molybdenum powder with low oxygen content, high dispersion, high porosity, and a particle size of 300-2000 nm. The ultrafine molybdenum powder has a core-shell structure with rare earth oxides as the core and elemental molybdenum layers as the shell; W element is dissolved in the elemental molybdenum layers.

[0081] The thickness of the doped molybdenum oxide powder in the hydrogen furnace is 3 mm.

[0082] Step 5): 2.6 g of nano-zirconium carbide (particle size of 50 nm) and the ultrafine molybdenum powder obtained above are placed in a ball mill for ball milling and mixing. The ball milling speed is 240 r / min to obtain molybdenum powder doped with nano-zirconium carbide.

[0083] Step 6): Molybdenum powder doped with nano-zirconium carbide is heated to 1000℃ and sintered for 1 hour, then heated to 1200℃ and sintered for 2 hours, then heated to 1400℃ and sintered for 2 hours, and finally heated to 2100℃ and sintered for 5 hours to obtain a molybdenum alloy; wherein the sintering pressure is 40 MPa.

[0084] The chemical composition of the molybdenum alloy prepared in this embodiment, after being formulated with the above-mentioned raw materials, should be as follows, and the chemical composition of the alloy should be controlled as follows:

[0085] C: 0.002wt%, Zr: 0.14wt%, Y: 0.35wt%, W: 0.26wt%, balance Mo.

[0086] Figure 1 This is a microstructure diagram of the molybdenum alloy prepared in Example 1; from Figure 1 It can be seen that the microstructure of the molybdenum alloy prepared in this embodiment includes a molybdenum matrix of BCC and a nano-reinforcing phase; wherein, the nano-reinforcing phase includes nano-Y₂O₃, nano-ZrO₂, nano-ZrC, and nano-Y x Zr y O (1.5x+2y) A mixed phase (typically a Y-Zr-O composite phase); wherein the nano-reinforcing phase and the molybdenum matrix exhibit a coherent or semi-coherent structure. Wherein, x is 0.1-5. The aforementioned nano-reinforcing phase and the molybdenum matrix all form coherent or semi-coherent interface structures.

[0087] This microstructure characteristic endows molybdenum alloys with excellent strengthening and toughening properties, and its mechanism of action is detailed below:

[0088] 1. Strength Enhancement Mechanism

[0089] On the one hand, the coherent / semi-coherent interface formed between the nano-reinforcing phase and the molybdenum matrix has the characteristics of low interfacial energy and strong interfacial bonding force, which can effectively pin dislocations and grain boundaries, producing a significant dispersion strengthening effect. At the same time, it can inhibit the growth of matrix grains during sintering, achieving grain refinement, and further improving the alloy strength through the grain refinement strengthening mechanism. On the other hand, the W element dissolved in the alloy can produce a solid solution strengthening effect, which, together with the aforementioned dispersion strengthening and grain refinement strengthening, forms a synergistic effect, jointly achieving a significant improvement in the alloy strength.

[0090] 2. Plasticity Enhancement Mechanism

[0091] The grain boundary brittleness of molybdenum alloys is a core factor restricting their strength-ductility balance. High interstitial oxygen content at grain boundaries leads to grain boundary embrittlement, significantly reducing grain boundary bonding strength and causing premature failure along the grain boundaries under stress, resulting in a significant decrease in plastic deformation capacity. In this embodiment, the added rare earth elements have a strong adsorption and fixation effect on interstitial atoms (especially oxygen), effectively purifying grain boundaries, significantly improving grain boundary bonding strength, inhibiting early grain boundary cracking, and thus greatly improving the alloy's plastic deformation capacity.

[0092] The properties of the molybdenum alloy prepared in this embodiment are as follows: tensile strength is above 600 MPa and elongation at break is greater than 30%.

[0093] Example 2

[0094] This embodiment provides a method for preparing a molybdenum alloy, including the following steps:

[0095] Step 1): With the aid of a water bath and a magnetic stirrer, 15.2g of anhydrous yttrium nitrate, 3.6g of anhydrous ammonium tungstate, and 1820g of anhydrous ammonium molybdate were dissolved in deionized water to obtain a homogeneous and clear solution, i.e., the precursor liquid. The water bath temperature was 65℃, the magnetic stirrer speed was 120 rpm, and the stirring time was 120 minutes.

[0096] Step 2): Add citric acid to the precursor liquid to adjust the pH to 1, then heat in a water bath to 80°C to form a complex precursor. After that, spray dry to obtain a dry mixed powder.

[0097] Step 3) The dried mixed powder is calcined in a muffle furnace; the calcination temperature is 450℃ and the calcination time is 2h to obtain doped molybdenum oxide powder.

[0098] Step 4): The doped molybdenum oxide powder is placed in a hydrogen furnace, heated to 550℃ and held for 2 hours, then heated to 800℃ and held for 4 hours to obtain ultrafine molybdenum powder with low oxygen content, high dispersion, high porosity, and a particle size of 300-2000 nm. The ultrafine molybdenum powder has a core-shell structure with rare earth oxides as the core and elemental molybdenum layers as the shell; W element is dissolved in the elemental molybdenum layers.

[0099] The thickness of the doped molybdenum oxide powder in the hydrogen furnace is 3 mm.

[0100] Step 5): 2.6 g of nano-zirconium carbide (particle size 50 nm) and ultrafine molybdenum powder are placed in a ball mill for ball milling and mixing. The ball milling speed is 240 r / min to obtain molybdenum powder doped with nano-zirconium carbide.

[0101] Step 6): Molybdenum powder doped with nano-zirconium carbide is heated to 1100℃ and sintered for 1 hour, then heated to 1250℃ and sintered for 2 hours, then heated to 1500℃ and sintered for 3 hours, and finally heated to 2100℃ and sintered for 6 hours to obtain a molybdenum alloy; wherein the sintering pressure is 40 MPa.

[0102] The chemical composition of the molybdenum alloy prepared in this embodiment, after being formulated with the above-mentioned raw materials, should be as follows, and the chemical composition of the alloy should be controlled as follows:

[0103] C: 0.0022wt%, Zr: 0.19wt%, Y: 0.37wt%, W: 0.24wt%, balance Mo.

[0104] The microstructure of the molybdenum alloy prepared in this embodiment includes a molybdenum matrix of BCC and nano-reinforcing phases; wherein, the nano-reinforcing phases include nano-Y₂O₃, nano-ZrO₂, nano-ZrC, and nano-Y x Zr y O (1.5x+2y) A mixed phase; wherein the nano-reinforcing phase and the molybdenum matrix are coherent or semi-coherent. Wherein, x is 0.1-5.

[0105] The properties of the molybdenum alloy prepared in this embodiment are as follows: its tensile strength is above 600 MPa and its elongation at break is greater than 27%.

[0106] The following describes the schemes of Examples 1 and 2: The microstructure of the molybdenum alloy mainly includes a molybdenum matrix and nano-reinforcing phases dispersed in the molybdenum matrix; wherein, the nano-reinforcing phases include Y₂O₃, ZrO₂, ZrC, and Y x Zr y O (1.5x+2y) The composite oxide, wherein the nano-reinforcing phase forms a coherent or semi-coherent interface structure with the molybdenum matrix. Specifically, in the microstructure of the molybdenum alloy, these nano-reinforcing phases mainly play the following roles: 1) They hinder grain boundary migration during sintering, resulting in significant grain refinement and strengthening; 2) The nano-reinforcing phases form a coherent structure with the matrix, exhibiting low interfacial energy and strong bonding, effectively pinning dislocations and grain boundaries, producing a strong dispersion strengthening effect; 3) ZrC can absorb oxygen during sintering, reducing the oxygen content in the molybdenum matrix; 4) Further optimization of the size and distribution of the nano-second phase through liquid-liquid doping and ball milling processes can purify grain boundaries, significantly improving grain boundary bonding strength; 5) In addition, the W element dissolved in the alloy can also play a solid solution strengthening role, enhancing the alloy's strength. Therefore, based on dispersion strength, grain refinement, and dislocation pile-up theory, the strength of the molybdenum alloy is improved.

[0107] Comparative Example 1

[0108] Comparative Example 1 provides a method for preparing a molybdenum alloy, comprising the following steps:

[0109] Step 1) Weigh 6 g of Y₂O₃, 3 g of ZrO₂, and 988.5 g of molybdenum powder and add them to a ball mill. Ball milling is performed under an Ar atmosphere to obtain rare earth-doped molybdenum powder. The ball mill speed is 220 r / min, and the ball milling time is 8 h.

[0110] Step 2) The rare earth-doped molybdenum powder obtained in Step 1 is heated to 1000℃ and sintered for 1 hour, then heated to 1200℃ and sintered for 2 hours, then heated to 1400℃ and sintered for 2 hours, and finally heated to 2100℃ and sintered for 5 hours to obtain a molybdenum alloy. The sintering pressure is 40 MPa.

[0111] The chemical composition of the molybdenum alloy prepared in Comparative Example 1 after the above raw materials were formulated is as follows:

[0112] Y: 0.37wt%, Zr: 0.20wt%, balance Mo.

[0113] The properties of the molybdenum alloy prepared in Comparative Example 1 are as follows: the room temperature tensile strength can reach more than 450 MPa, and the room temperature elongation at break is more than 6%.

[0114] Figure 2 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 1. Comparative Example 1 uses a traditional solid-solid doping method. The second phase is prone to agglomerate and grow at the grain boundaries. The second phase is large in size, resulting in poor grain refinement. Furthermore, dislocations cannot cut through the second phase to generate dislocation pile-up, which leads to stress concentration and makes it easy to act as a crack source. In addition, the alloy lacks the solid solution strengthening effect of W element, so the overall performance is poor.

[0115] The molybdenum alloy prepared in Comparative Example 1 exhibits poor performance, primarily due to the following reasons: First, the absence of W element in the molybdenum alloy results in a lack of solid solution strengthening contribution; second, the coarse size of the second phase in the molybdenum alloy leads to poor interfacial bonding with the matrix, significantly weakening the effects of fine grain strengthening and dispersion strengthening; third, the coarse second phase tends to agglomerate at grain boundaries, becoming the source of crack initiation and propagation, further deteriorating the overall mechanical properties of the alloy; and fourth, the large grain size and high degree of recrystallization further exacerbate grain boundary segregation, weakening grain boundary performance.

[0116] Comparative Example 2

[0117] Comparative Example 2 provides a method for preparing a molybdenum alloy, comprising the following steps:

[0118] Step 1): 14.2 g of yttrium tetraacetate, 8 g of zirconium acetate, 3.6 g of ammonium tungstate, and 1820 g of ammonium molybdate were placed in deionized water and heated with stirring to promote the dissolution of the raw materials, obtaining a precursor solution (a uniformly mixed, clear solution). Heating was performed using a water bath at 65°C, and stirring was done with a magnetic stirrer at 120 rpm. The heating and stirring process lasted for 120 minutes.

[0119] Step 2): Add citric acid to the precursor solution to adjust the pH value to 1, heat in a water bath to 80°C to obtain the complex precursor in the solution, and then spray dry to obtain a dry mixed powder.

[0120] Step 3): In a muffle furnace, the mixed powder is calcined at 450°C for 2 hours to obtain doped molybdenum oxide powder.

[0121] Step 4): The doped molybdenum oxide powder is placed in a hydrogen furnace and heated to 550°C for 2 hours, then heated to 800°C and held for 4 hours to obtain ultrafine molybdenum powder with low oxygen content, high dispersion, high porosity and a particle size of 500 nanometers; wherein the particle size of the ultrafine molybdenum powder is 300-2000 nm.

[0122] The thickness of the molybdenum oxide powder in the hydrogen furnace is 3 mm.

[0123] Step 5): Heat ultrafine molybdenum powder with a particle size of 500 nm to 1000℃ and sinter for 1 h, then raise the temperature to 1250℃ and sinter for 2 h, then raise the temperature to 1500℃ and sinter for 3 h, and finally raise the temperature to 2100℃ and sinter for 6 h. The sintering pressure is 40 MPa to obtain sintered molybdenum alloy.

[0124] The chemical composition of the molybdenum alloy prepared in this embodiment after being formulated with the above-mentioned raw materials is as follows: Y: 0.21wt%, Zr: 0.19wt%, W: 0.24wt%, with the balance being Mo.

[0125] The properties of the molybdenum alloy prepared in Comparative Example 2 are as follows: its tensile strength is above 570 MPa and its elongation at break is greater than 22%.

[0126] Figure 3 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 2. Figure 3 It can be seen that: in Comparative Example 2, the second phase at the grain boundary is small in size, which can effectively pin the grain boundary, refine the grains, reduce the oxygen content per unit grain boundary area and improve the performance of the matrix. However, compared with the Example, it lacks the deoxidation effect of ZrC, and the grain boundary bonding strength is lower than that of the Example. Therefore, the performance is slightly lower than that of the Example.

[0127] Compared with Comparative Example 2, the molybdenum alloy prepared in this embodiment of the invention introduces zirconium carbide through ball milling, which can further improve the distribution of the second phase. Furthermore, zirconium carbide can effectively reduce the oxygen content in the matrix and strengthen the bonding ability of grain boundaries during sintering, which is beneficial to improving the elongation.

[0128] Comparative Example 3

[0129] Comparative Example 3 provides a method for preparing a molybdenum alloy, comprising the following steps:

[0130] Step 1): Weigh 21.3g of yttrium tetraacetate, 8g of zirconium acetate, 3.6g of ammonium tungstate, and 1820g of ammonium molybdate into deionized water and heat and stir to promote the dissolution of the raw materials, obtaining a precursor solution (a uniformly mixed, clear solution). Heating is performed using a water bath at 65℃, and stirring is done with a magnetic stirrer at 120 rpm. The heating and stirring process lasts for 120 minutes.

[0131] The remaining process steps are the same as in Comparative Example 2. A sintered molybdenum alloy with a tensile strength of over 500 MPa and an elongation at break of over 1% is obtained.

[0132] The chemical composition of the molybdenum alloy prepared in Comparative Example 3 is as follows: Y: 0.60 wt%, Zr: 0.19 wt%, W: 0.29 wt%, with the balance being Mo.

[0133] Figure 4 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 3. Figure 4 It can be seen that: in Comparative Example 3, due to the excessive addition of rare earth elements, the volume fraction of rare earth oxides and rare earth-zirconium composite oxides generated in situ in the alloy exceeded the standard, the size of the second phase was out of control, and it was easy to agglomerate and coarsen at the grain boundaries, inducing stress concentration, weakening the grain boundary strength, and failing to exert the dispersion pinning effect of the nano-reinforcing phase; at the same time, the grain refinement effect of this comparative example was similar to that of Example 2, without any additional grain refinement strengthening gain, and the strength and plasticity of the final molybdenum alloy were significantly lower than those of the corresponding example of this application.

[0134] Comparative Example 4

[0135] Comparative Example 4 provides a method for preparing a molybdenum alloy, comprising the following steps:

[0136] Step 1): Weigh 1820g of ammonium molybdate and place it in deionized water. Heat and stir the solution to promote dissolution and obtain a precursor solution (a uniformly mixed, clear solution). Heating is performed using a water bath at 65℃, and stirring is done with a magnetic stirrer at 120 rpm. The heating and stirring process lasts for 120 minutes.

[0137] The remaining process steps are the same as those in Comparative Example 2.

[0138] The chemical composition of the molybdenum alloy prepared in this comparative example after being formulated with the above raw materials is as follows: Y: 0 wt%, Zr: 0 wt%, W: 0 wt%, with the balance being Mo.

[0139] Figure 5 This is a microstructure diagram of the molybdenum alloy prepared in Comparative Example 4. Figure 5It can be seen that Comparative Example 4 did not add the strengthening phase-related elements defined in this invention, forming a core difference from the embodiments of this invention. Because this comparative example did not introduce the corresponding strengthening phase elements, it could not generate a uniformly dispersed nano-strengthening phase in situ within the molybdenum matrix, completely lacking the dispersion strengthening effect; nor could it achieve matrix solid solution with corresponding alloying elements, thus failing to obtain the performance gains brought by solid solution strengthening. Due to the lack of the pinning and retardation effect of the nano-second phase on grain boundaries, the molybdenum matrix grains underwent significant abnormal growth during the sintering process, with grain sizes much larger than those in the embodiments of this invention. The complete absence of the core strengthening mechanism, coupled with the adverse effect of matrix grain coarsening, ultimately resulted in the molybdenum alloy prepared in Comparative Example 4 having significantly lower strength and plasticity than the embodiments of this invention.

[0140] The properties of the molybdenum alloy prepared in Comparative Example 4 are as follows: its tensile strength is above 440 MPa and its elongation at break is greater than 4%.

[0141] The molybdenum alloy prepared in Comparative Example 4 is pure molybdenum. Compared with the examples, pure molybdenum does not have the solid solution strengthening of W element, nor the dispersion strengthening and grain refinement effect of rare earth oxides, so its performance is poor.

[0142] Figure 6 These are tensile property graphs of the molybdenum alloys prepared in Example 1 and Comparative Examples 1-4. From... Figure 6 It can be seen that the mechanical properties of the molybdenum alloy prepared in the embodiments of the present invention are significantly superior to those of comparative examples 1-4.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A molybdenum alloy, characterized in that, The molybdenum alloy comprises the following chemical components by weight percentage: C: 0.0015wt%-0.0025wt%, Zr: 0.10wt%-0.19wt%, rare earth Y: 0.25wt%-0.40wt%, W: 0.22wt%-0.28wt%, balance Mo; The microstructure of the molybdenum alloy comprises a molybdenum matrix of BCC and a nano-reinforced phase; wherein the nano-reinforced phase comprises nano-Y2O3, nano-ZrO2, nano-ZrC, nano-Y x Zr y O (1.5x+2y) mixed phase; wherein the nano-reinforced phase and the molybdenum matrix are in a coherent or semi-coherent structure; wherein x is 0.1-5.

2. The molybdenum alloy according to claim 1, characterized in that, The nano-reinforced phase is spherical with a size of 10nm-200nm.

3. The molybdenum alloy according to claim 1, characterized in that, The strengthening methods of the molybdenum alloy include nanophase dispersion strengthening and tungsten solid solution strengthening.

4. The molybdenum alloy according to claim 1, characterized in that, The molybdenum alloy has a tensile strength greater than 600 MPa and an elongation at break greater than 27% at room temperature.

5. The method for preparing the molybdenum alloy according to any one of claims 1-4, characterized in that, The preparation method of the molybdenum alloy includes the following steps: Step 1): Add ammonium molybdate, ammonium tungstate, and rare earth yttrium salt to water, and heat and stir to promote dissolution, to obtain the precursor liquid; Step 2): The precursor liquid is heated to form a complex precursor; The complex precursor is dried to obtain a mixed powder; Step 3): The mixed powder is calcined to obtain doped molybdenum oxide powder; Step 4): The doped molybdenum oxide powder is reduced under a hydrogen atmosphere to obtain molybdenum powder; wherein the molybdenum powder is doped with rare earth elements and W elements; Step 5): The molybdenum powder and nano-zirconium carbide are ball-milled to obtain molybdenum powder doped with nano-zirconium carbide; Step 6): The molybdenum powder doped with nano-zirconium carbide is sintered to obtain a molybdenum alloy.

6. The method for preparing the molybdenum alloy according to claim 5, characterized in that, The ammonium molybdate is one or more of ammonium dimolybdate, ammonium tetramolybdate, and ammonium heptamolybdate; the ammonium tungstate is one or two of ammonium paratungstate and ammonium metatungstate; the rare earth yttrium salt is selected from yttrium acetate and / or yttrium nitrate.

7. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 1), the temperature of the heating and stirring treatment is 60℃-80℃, the rotation speed of the heating and stirring treatment is greater than 80 revolutions per minute, and the duration of the heating and stirring treatment is greater than 30 minutes.

8. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 2): Citric acid is added to the precursor liquid to adjust the pH value of the liquid to 1-3, making the solution clear, and then it is heated to form a complex precursor.

9. The method for preparing the molybdenum alloy according to claim 8, characterized in that, In step 2), the temperature of the heat treatment is 65℃-85℃.

10. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 2), the drying process is selected from vacuum drying, spray drying, and freeze drying.

11. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 3): the roasting atmosphere is atmospheric, the roasting temperature is 450℃-650℃, and the roasting time is 2h-4h.

12. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 4): Under a hydrogen reducing atmosphere, the doped molybdenum oxide powder is heated to 550℃-650℃ and held for 2-4 hours, and then heated to 700℃-950℃ and held for 2-8 hours to carry out reduction treatment to obtain molybdenum powder; wherein, during the reduction treatment, the thickness of the doped molybdenum oxide powder is 3mm-5mm.

13. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 4), the particle size of the molybdenum powder is 300nm-2000nm.

14. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 5), the particle size of the nano-zirconium carbide is 10nm-150nm.

15. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 5): The molybdenum powder has a core-shell structure with rare earth oxides as the core and elemental molybdenum layers as the shell; wherein, W element is dissolved in elemental molybdenum layers.

16. The method for preparing the molybdenum alloy according to claim 5, characterized in that, In step 6): The molybdenum powder doped with nano-zirconium carbide is heated to 1000℃-1100℃ for sintering for 1h-2.5h, then heated to 1150℃-1350℃ for sintering for 2-4h, then heated to 1400℃-1600℃ for sintering for 2-4h, and finally heated to 2000℃-2200℃ for sintering for 4-8h to obtain a molybdenum alloy, wherein the sintering pressure is 40-80MPa.

Images