In-situ generation of high-stable nano-metallic particle dispersion strengthened Mo alloy and preparation method thereof

Abstract

The application relates to an in-situ generated high-stability nano-metal particle dispersion reinforced Mo alloy and a preparation method thereof, the Mo alloy is prepared by pressure sintering through a powder metallurgy method; the Mo alloy comprises 0.4-0.7wt% boride ceramic powder HfB2 and 99.3-99.6wt% metal Mo powder according to mass percentage; and the microstructure of the Mo alloy comprises Mo grains and Hf particles with nano-cubic structures which are uniformly distributed in the Mo grains. The B source is introduced by the boride ceramic powder HfB2 to react with the impurity O in the Mo to generate B2O3 to purify the grain boundary and in-situ reaction to generate the Hf particles with nano-cubic structures which are uniformly distributed in the Mo grains, and the most particles are uniformly distributed in the Mo grains, so that the problems that the traditional dispersion reinforced Mo alloy particles are prone to be gathered at the grain boundary, the performance is reduced in the subsequent service process, and even the particles become crack sources and the like can be solved, so that the toughness and the strength of the Mo are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of Mo alloy structural materials technology, specifically relating to an in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy and its preparation method. Background Technology

[0002] Mo alloys possess a range of excellent physical and chemical properties, including a high melting point (~2620 ℃), good high-temperature strength, corrosion resistance, and good thermal conductivity. They are also widely used in aerospace engineering as high-temperature structural materials. However, despite these advantages, pure Mo still suffers from poor room-temperature plasticity, low high-temperature strength, recrystallization brittleness, and radiation embrittlement, significantly limiting its application range.

[0003] Traditional research on high-performance Mo alloys mainly focuses on grain refinement strengthening, solid solution strengthening, and dispersion strengthening. Grain refinement strengthening primarily improves the strength of the metal by refining the grain size of polycrystalline materials; solid solution strengthening is a phenomenon where local lattice distortion caused by solute atoms increases the strength and hardness of the matrix. Both of these strengthening mechanisms only improve the material's strength, while dispersion strengthening can synergistically address the material's comprehensive mechanical and thermal properties. Dispersion strengthening involves introducing uniformly dispersed nanoparticles such as oxides Y₂O₃, La₂O₃, or carbides ZrC, TiC to disperse and strengthen Mo grains and grain boundaries. According to the strengthening mechanism of dispersed particle-doped Mo alloys, dispersed particles within the Mo grains are more effective at improving the material's strength and toughness than dispersed particles at grain boundaries. This is mainly because intergranular dispersed particles tend to aggregate at grain boundaries, becoming stress concentration points during subsequent tensile deformation or service life, potentially leading to cracking between the particles and the Mo matrix. For example, in their paper “Coupling effect of intergranular and intragranular particles on ductile fracture of Mo–La2O3 alloys”, Materials Science & Engineering A, 640(2015)320329, Cheng et al. reported that by adding La2O3 to Mo, with La2O3 acting as dispersed particles to strengthen Mo alloys, they prepared intergranular particles with a size of 230 nm and a particle ratio as high as 28% distributed at the grain boundaries.

[0004] In summary, traditional nanoparticles used as dispersed particles to reinforce Mo alloys cannot simultaneously achieve the high strength and plasticity of Mo alloy materials, nor can they achieve high strength and high toughness at high temperatures. As a result, the comprehensive mechanical properties of Mo alloys cannot be further improved, thus failing to meet the requirements of space reactors for key structural materials. To address the above problems, this invention proposes an in-situ method for generating highly stable nano-metal particles to reinforce Mo alloys and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide an in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy and its preparation method in order to solve the above-mentioned problems.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] This invention provides an in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy, wherein the Mo alloy is prepared by pressure sintering using powder metallurgy.

[0008] The Mo alloy comprises, by mass percentage, 0.4-0.7 wt% boride ceramic powder HfB2 and 99.3-99.6 wt% metallic Mo powder;

[0009] The microstructure of the Mo alloy includes Mo grains and Hf particles with a nanocubic structure uniformly distributed inside the Mo grains.

[0010] As a further optimization of the present invention, the average particle size of the boride ceramic powder HfB2 is 50~500nm, and the average particle size of the metallic Mo powder is 0.5~5.0 μm.

[0011] As a further optimization of the present invention, in the microstructure of the Mo alloy, the average grain size of Mo grains is 6.7 μm.

[0012] As a further optimization of the present invention, in the microstructure of the Mo alloy, more than 80% of the Hf particles are uniformly distributed inside the Mo grains, and the remaining particles are distributed at the grain boundaries of the Mo grains.

[0013] This invention also provides a method for preparing a highly stable nano-metal particle dispersion-reinforced Mo alloy generated in situ as described above, which is produced by powder metallurgy and includes the following steps:

[0014] Step 1: According to the formula, place the metallic Mo powder and boride ceramic powder HfB2 in a protective atmosphere, vacuum, or alcohol and mix them evenly to obtain a mixed powder.

[0015] Step 2: Place the mixed powder obtained in Step 1 into a graphite mold, then place the graphite mold under vacuum or a protective atmosphere and sinter it under pressure at 1500~1800 ℃ for 1~10 h. Finally, after cooling in the furnace, the sintered Mo alloy block is obtained.

[0016] As a further optimization of the present invention, in steps one and two, the protective atmosphere is one of hydrogen atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere or neon atmosphere.

[0017] As a further optimization of the present invention, in steps one and two, the vacuum degree of the vacuum condition is ≤ 20 Pa.

[0018] As a further optimization of the present invention, in step two, the pressure condition for pressure sintering is 21 kN.

[0019] The beneficial effects of this invention are as follows:

[0020] The preparation process of this invention is simple. By introducing boron source through boride ceramic powder HfB2, it reacts with impurity O in Mo to generate B2O3, which purifies the grain boundaries and generates Hf with a nano-cubic structure that is uniformly distributed inside the Mo grains. The majority of the particles are uniformly distributed inside the Mo grains, which can solve the problem that traditional dispersion-strengthened Mo alloy particles are prone to agglomeration at the grain boundaries, leading to performance degradation or even becoming crack sources during subsequent service. As a result, the toughness and strength of Mo are greatly improved.

[0021] This invention develops a heating and pressurizing sintering process. Heating and pressurizing simultaneously can effectively increase the density of the material and significantly improve its performance.

[0022] Performance tests show that the Mo alloy prepared by this invention has an ultimate tensile strength of 754 MPa and an elongation of ~22.5% at a high temperature of 400 ℃. Both its strength and plasticity are significantly better than those of pure Mo and Mo alloys, which are widely used in industry.

[0023] Furthermore, the sintered sample was subjected to high-temperature annealing at 1000 °C for 100 h, and the microstructure and mechanical properties of the annealed sample were characterized. The results showed that after high-temperature annealing, most of the particles in the microstructure of the sample were still uniformly dispersed inside the Mo grains, and the tensile properties at 400 °C were comparable to those of the sintered sample. Attached Figure Description

[0024] Figure 1 This is the sintering process curve provided by the present invention;

[0025] Figure 2The results are obtained by elemental line scanning of the sintered high-strength and high-toughness Mo alloy prepared in Example 1 of the present invention using an energy dispersive spectroscopy (EDS) instrument.

[0026] Figure 3 The electron backscattering results are those of the pure Mo sintered body (a) prepared in Comparative Example 1 and the sintered high-strength and high-toughness Mo alloy (b) obtained in Example 1 of this invention.

[0027] Figure 4 The transmission electron microscopy results are those of the sintered high-strength and high-toughness Mo alloy (a) obtained in Example 1 of the present invention and the Mo-HfO2 alloy (b) obtained in Comparative Example 2.

[0028] Figure 5 The tensile stress-strain curves of the sintered high-strength and high-toughness Mo alloy (a) obtained in Example 1 of the present invention and the Mo-HfO2 alloy (b) obtained in Comparative Example 2 at 400 °C are shown. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0030] In the following embodiments, the metallic Mo powder was obtained by commercial purchase or by conventional methods in the art, and the boride ceramic powder HfB2 was obtained by borothermal reduction, with a purity of 99%.

[0031] Example 1

[0032] The sintered high-strength and high-toughness Mo alloy disclosed in this embodiment is prepared by powder metallurgy, and the preparation method includes the following steps:

[0033] Step 1: Mix 99.3 wt% metallic Mo powder and 0.7 wt% boride ceramic powder HfB2 uniformly by mechanical ball milling in an argon atmosphere to obtain a mixed powder, wherein the average particle size of metallic Mo powder is about 2.0 μm and the average particle size of boride ceramic powder HfB2 is about 170 nm.

[0034] Step Two: Place the mixed powder obtained in Step One into a graphite mold, and then place the graphite mold under a vacuum of 20 Pa, and perform the following steps... Figure 1 The powder was densified and sintered using a three-step heating and two-step pressurization method, held at the temperature for 2 hours, and finally cooled in the furnace to obtain a sintered high-strength and high-toughness Mo alloy.

[0035] The microstructure and mechanical properties of the sintered high-strength and high-toughness Mo alloy prepared in Example 1 were analyzed.

[0036] Figure 2 The image shows an EDS energy spectrum of the sintered high-strength and high-toughness Mo alloy. As can be seen from the image, the structure of the sintered high-strength and high-toughness Mo alloy consists of a Mo matrix and Hf particles with a nano-cubic structure. The boride ceramic powder HfB2 reacts in situ with the impurity oxygen in Mo, absorbs the impurity oxygen in the grain boundary, reduces the embrittlement effect of impurity oxygen on Mo, and generates Hf particle dispersion-strengthened Mo alloy.

[0037] Figure 3 (b) shows the electron backscattering results of the sintered high-strength and high-toughness Mo alloy obtained in Example 1. As can be seen from the figure, the density of the sintered high-strength and high-toughness Mo alloy is 99%, and the average grain size of Mo grains is 6.7 μm.

[0038] Figure 4 (a) shows the transmission electron microscopy results of the sintered high-strength and high-toughness Mo alloy obtained in Example 1. As can be seen from the figure, the arrows indicate that most of the particles are uniformly distributed inside the Mo grains.

[0039] Figure 5 The figure shows the tensile stress-strain curve of the sintered high-strength and high-toughness Mo alloy obtained in Example 1 at 400 °C. As can be seen from the figure, at 400 °C, the ultimate tensile strength of the sintered high-strength and high-toughness Mo alloy reaches approximately 754 MPa and the elongation reaches ~22.5%.

[0040] Example 2

[0041] The sintered high-strength and high-toughness Mo alloy disclosed in this embodiment is prepared by powder metallurgy, and the preparation method includes the following steps:

[0042] Step 1: Mix 99.5 wt% metallic Mo powder and 0.5 wt% boride ceramic powder HfB2 in an argon atmosphere by mechanical ball milling to obtain a mixed powder; wherein the average particle size of metallic Mo powder is about 2.0 μm and the average particle size of HfB2 is about 170 nm.

[0043] Step Two: Place the mixed powder obtained in Step One into a graphite mold, then place the graphite mold under a vacuum of 20 Pa, and follow the steps outlined above. Figure 1 The sintering conditions defined by the sintering process curve shown were used for pressure sintering, which was held at a temperature for 2 hours. Finally, after furnace cooling, a sintered high-strength and high-toughness Mo alloy was obtained.

[0044] Tests showed that the sintered high-strength and high-toughness Mo alloy obtained in Example 2 had an ultimate tensile strength of approximately 700 MPa and an elongation of ~17% at 400 °C.

[0045] Example 3

[0046] The sintered high-strength and high-toughness Mo alloy disclosed in this embodiment is prepared by powder metallurgy, and the preparation method includes the following steps:

[0047] Step 1: Mix 99.4 wt% metallic Mo powder and 0.6 wt% boride ceramic powder HfB2 in an argon atmosphere by mechanical ball milling to obtain a mixed powder; wherein the average particle size of metallic Mo powder is about 2.0 μm and the average particle size of HfB2 is about 170 nm.

[0048] Step Two: Place the mixed powder obtained in Step One into a graphite mold, then place the graphite mold under a vacuum of 20 Pa, and take the following steps... Figure 1 The powder was densified and sintered using a three-step heating and two-step pressurization method, held at the temperature for 2 hours, and finally cooled in the furnace to obtain a sintered high-strength and high-toughness Mo alloy.

[0049] Tests showed that the sintered high-strength and high-toughness Mo alloy obtained in Example 3 had an ultimate tensile strength of approximately 720 MPa and an elongation of ~20% at 400 °C.

[0050] Example 4

[0051] The sintered high-strength and high-toughness Mo alloy disclosed in this embodiment is prepared by powder metallurgy, and the preparation method includes the following steps:

[0052] Step 1: Mix 99.6 wt% metallic Mo powder and 0.4 wt% boride ceramic powder HfB2 uniformly by mechanical ball milling in an argon atmosphere. The average particle size of metallic Mo powder is about 2.0 μm and the average particle size of HfB2 is about 170 nm to obtain mixed powder.

[0053] Step Two: Place the mixed powder obtained in Step One into a graphite mold, then place the graphite mold under a vacuum of 20 Pa, and take the following steps... Figure 1 The powder was densified and sintered using a three-step heating and two-step pressurization method, held at the temperature for 2 hours, and finally cooled in the furnace to obtain a sintered high-strength and high-toughness Mo alloy.

[0054] Tests showed that the sintered high-strength and high-toughness Mo alloy obtained in Example 4 had an ultimate tensile strength of approximately 700 MPa and an elongation of ~18% at 400 °C.

[0055] Comparative Example 1

[0056] The pure Mo sintered bulk material disclosed in this comparative example is prepared by powder metallurgy, and the preparation method includes the following steps:

[0057] Step 1: 100 wt% metallic Mo powder is uniformly homogenized by mechanical ball milling in an argon atmosphere. The average particle size of the metallic Mo powder is approximately 2.0 μm.

[0058] Step Two: Place the Mo powder treated in Step One into a graphite mold. Then, place the graphite mold under a vacuum of 20 Pa and perform the following steps: Figure 1 The powder was densified and sintered using a three-step heating and two-step pressurization method, held at the temperature for 2 hours, and finally cooled in the furnace to obtain pure Mo sintered blocks.

[0059] Figure 3 (a) shows the electron backscattering results of the pure Mo sintered bulk obtained in Comparative Example 1. As can be seen from the figure, the average grain size of Mo grains in the pure Mo sintered bulk is 15.8 μm. Compared with the pure Mo sintered bulk, the Mo grains of the sintered high strength and toughness Mo alloy obtained in Example 1 are refined by about 9.1 μm.

[0060] In addition, tests showed that the sintered pure Mo alloy obtained in Comparative Example 1 had no plasticity at 400 °C.

[0061] Comparative Example 2

[0062] Unlike Example 1, this comparative example utilizes oxide ceramic powder HfO2 to disperse and reinforce metallic Mo to obtain a Mo-HfO2 alloy. The preparation method includes the following steps:

[0063] Step 1: Mix 99.3 wt% metallic Mo powder and 0.7 wt% oxide ceramic powder HfO2 uniformly by mechanical ball milling in an argon atmosphere to obtain a mixed powder, wherein the average particle size of metallic Mo powder is about 2.0 μm and the average particle size of HfO2 powder is 40 nm.

[0064] Step Two: Place the mixed powder obtained in Step One into a graphite mold, then place the graphite mold under a vacuum of 20 Pa, and take the following steps... Figure 1 The powder was densified and sintered using a three-step heating and two-step pressurization method, held at the temperature for 2 hours, and finally cooled in the furnace to obtain the Mo-HfO2 alloy.

[0065] Figure 4(b) shows the transmission electron microscopy results of the Mo-HfO2 alloy obtained in Comparative Example 2. As can be seen from the figure, the arrows indicate that most of the HfO2 particles are distributed at the grain boundaries of Mo grains. This can cause performance degradation or even become crack initiation sites in the Mo alloy during service, which is detrimental to improving the strength and toughness of the alloy.

[0066] Figure 5 The tensile stress-strain curves of the Mo-HfO2 alloy at 400 °C are presented. As can be seen from the figure, at 400 °C, the ultimate tensile strength and elongation of the Mo-HfO2 alloy are both lower than those of the sintered high-strength and high-toughness Mo alloy obtained in Example 1. The elongation of the sintered high-strength and high-toughness Mo alloy obtained in Example 1 is approximately 7% higher than that of the Mo-HfO2 alloy.

[0067] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A Mo alloy reinforced by in-situ generation of highly stable nano-metal particles, characterized in that, The Mo alloy is prepared by pressure sintering using powder metallurgy; wherein, the Mo alloy comprises, by mass percentage, 0.4~0.7wt% boride ceramic powder HfB2 and 99.3~99.6wt% metallic Mo powder; the microstructure of the Mo alloy includes Mo grains and Hf particles with a nanocubic structure uniformly distributed inside the Mo grains. The in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy is prepared by powder metallurgy, and the preparation method includes the following steps: Step 1: According to the formula, place the metallic Mo powder and boride ceramic powder HfB2 in a protective atmosphere, vacuum, or alcohol and mix them evenly to obtain a mixed powder. Step 2: Place the mixed powder obtained in Step 1 into a graphite mold, then place the graphite mold under vacuum or a protective atmosphere, and sinter under pressure at 1500~1800℃ for 1~10 h. Finally, after furnace cooling, a Mo alloy sintered block is obtained; wherein, the vacuum degree of the vacuum condition is ≤ 20 Pa; and the pressure condition of the pressure sintering is 21 kN.

2. The in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy according to claim 1, characterized in that: The average particle size of the boride ceramic powder HfB2 is 50~500 nm, and the average particle size of the metallic Mo powder is 0.5~5.0 μm.

3. The in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy according to claim 1, characterized in that, In the microstructure of the Mo alloy, the average grain size of Mo grains is 6.7 μm.

4. The in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy according to claim 1, characterized in that, In the microstructure of the Mo alloy, more than 80% of the Hf particles are uniformly distributed inside the Mo grains, while the remaining particles are distributed at the grain boundaries of the Mo grains.

5. The in-situ generated highly stable nano-metal particle dispersion-reinforced Mo alloy according to claim 1, characterized in that, In steps one and two, the protective atmosphere is one of hydrogen atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere or neon atmosphere.

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