Molybdenum alloy with multimodal grain heterostructure and high strength and toughness and preparation method thereof

Abstract

The invention discloses a multi-peak grain heterostructure high-strength and high-toughness molybdenum alloy and a preparation method thereof, and the molybdenum alloy comprises the following components in percentage by weight: 98-99.5% of molybdenum and 0.5-1.5% of carbide, the preparation method of the molybdenum alloy comprises the following steps that molybdenum powder and carbide powder are mixed and then subjected to ball milling, mixed powder is obtained and subjected to pressureless hydrogen sintering after being pressed, and the molybdenum alloy of the multi-peak grain structure is obtained by controlling ball milling process parameters and the second phase content. The sintering activation energy of the powder is improved through the ball milling technology, and the second-phase particles are used for inhibiting grain growth in the sintering process to regulate and control the multi-peak grain structure. The prepared heterostructure molybdenum alloy has a controllable microstructure and excellent comprehensive performance, the raw materials and the preparation process are simple, and the heterostructure molybdenum alloy has wide engineering application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of refractory metal powder metallurgy preparation, and in particular to a multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy and a preparation method thereof. Background Art

[0002] Molybdenum alloy has excellent properties such as high melting point, high strength, creep resistance, corrosion resistance and low thermal expansion coefficient. It is widely used in aerospace, mechanical processing, military equipment, nuclear energy, metallurgy, especially in high temperature fields. With the rapid development of high temperature application fields such as aerospace and mechanical manufacturing, higher requirements are put forward for the high temperature strength and machinability of molybdenum alloys, making it difficult for traditional dispersion-strengthened and solid solution-strengthened molybdenum alloys to meet the needs of high-end application fields. Due to the BCC crystal structure of molybdenum, molybdenum alloys have intrinsic brittleness. In addition, doped alloying elements or second phase particles usually form intergranular second phase particles in molybdenum alloys, making molybdenum alloys exhibit poor room temperature strength and ductility, which in turn leads to difficulties in subsequent mechanical processing and insufficient high temperature strength of molybdenum alloy products. These problems seriously limit the widespread application of molybdenum alloys in high temperature materials in the future.

[0003] At present, the methods for improving the strength and toughness of molybdenum alloys mainly include: alloying, severe plastic deformation, and multi-component second phase doping. Alloying is to purify the molybdenum alloy grain boundaries and improve the plasticity of the molybdenum alloy by adding one or more elements such as boron, carbon, titanium, hafnium, zirconium, silicon, tantalum, and rhenium. However, the sintered molybdenum alloy has low strength due to the coarse grain size. Although severe plastic deformation can refine the grains and improve the strength and plasticity of the alloy, the plasticity improvement is limited due to the excessive degree of work hardening. When exposed to a high temperature environment, it will promote high-temperature softening mechanisms such as recovery and recrystallization, resulting in a decrease in high-temperature strength. For multi-component second phase doping, the preparation methods of multi-component second phase doped molybdenum alloys disclosed in patents CN 104651696A, CN 114134386A, and CN 11118755983A use nano-scale TiC, WC and TiC-Y 2 O 3 Powder reinforced molybdenum alloys, these nano-scale doped phases form dispersed second phase particles in situ in the molybdenum matrix, and at the same time act as deoxidizers to adsorb oxygen impurities at the grain boundaries. However, while the strength is increased by pinning dislocations, the plastic deformation of the alloy is also inhibited, resulting in limited improvement in the plasticity of the molybdenum alloy, or even increasing the strength of the molybdenum alloy at the expense of plasticity. Therefore, it is difficult to synergistically improve the strength and plasticity of molybdenum alloys through traditional means and a single strengthening mechanism. A new preparation process for molybdenum alloys is urgently needed to improve the problems of coarse grains and poor strength and toughness of molybdenum alloys under existing preparation methods. Summary of the invention

[0004] One of the purposes of the present invention is to provide a multi-peak grain heterogeneous structure high strength and toughness molybdenum alloy to solve the defects of the molybdenum alloy in the prior art such as insufficient strength and plasticity, increase the density of the molybdenum alloy, and improve the machinability of the molybdenum alloy.

[0005] The second object of the present invention is to provide a method for preparing the multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy.

[0006] The invention provides a multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy, which comprises the following components by weight percentage: molybdenum: 98% to 99.5%, carbide: 0.5% to 1.5%.

[0007] Furthermore, in the multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy, the ultrafine grain size is 0.2 to 2 microns, the fine grain size is 2 to 6 microns, and the coarse grain size is 6 to 50 microns.

[0008] The heterogeneous structure high-strength and toughness molybdenum alloy has a relative density of 98% to 99%, a micro-Vickers hardness of 150-300 HV, a tensile strength of 588 to 638 MPa, and a strain of 30% to 65%.

[0009] The present invention also provides a method for preparing the multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy, comprising the following steps:

[0010] S1. Weigh molybdenum powder and carbide powder according to a preset ratio and mix them, ball milling to obtain a mixed powder;

[0011] S2. The mixed powder obtained in step S1 is pressed to obtain a compact;

[0012] S3. The compact obtained in step S2 is placed in a sintering furnace for sintering. After sintering, the compact is cooled to room temperature in the furnace to obtain the multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy.

[0013] Furthermore, in step S1, in the mixed powder, the mass proportion of the carbide powder is 0.5% to 1.5%, and the remainder is molybdenum powder.

[0014] The carbide is one or more of titanium carbide, zirconium carbide and hafnium carbide.

[0015] Preferably, the carbide powder is micron-sized hafnium carbide powder.

[0016] Hafnium carbide has good high-temperature stability, can hinder the grain growth during the sintering process, play a role in refining the grains, and can also be used as a deoxidizer to remove oxygen impurities in the powder.

[0017] Furthermore, in step S1, a drum mixer is used for mixing, the mixer speed is 110 to 130 r / min, and the mixing time is 12 to 28 h.

[0018] A planetary ball mill is used for ball milling, the ball-to-material ratio of the ball milling is (8-15):1, the ball milling speed is 200-500 r / min, the ball milling time is 12-48 h, and the ball milling atmosphere is an inert gas.

[0019] Preferably, the ball milling process uses a WC carbide pot, and the ball milling medium is a WC carbide ball.

[0020] The ball mill was operated alternately, and no process control agents such as anhydrous ethanol and stearic acid were added during the ball milling. Powder was taken and ground and dispersed every 6 hours, and then vacuumed and inflated again to continue the ball milling.

[0021] Furthermore, in step S2, the pressing pressure is 150-250 MPa and the pressing time is 60-120 s.

[0022] Furthermore, in step S3, the sintering process is: in a hydrogen atmosphere, first heating to 1000-1100°C, keeping warm for 1.5-2.5 hours, then heating to 1700-1900°C, keeping warm for 1-2 hours, after the insulation is completed, cooling to 500°C, and then cooling to room temperature with the furnace.

[0023] During the sintering process, the temperature is raised and lowered at a rate of 8 to 10°C / min.

[0024] Principle of the present invention:

[0025] The present invention improves the sintering activation energy of Mo powder by ball milling, so that the compact can be quickly densified without external field assistance. In addition, micron-sized second phase particles are broken into nanoparticles dispersed in the Mo powder during the ball milling process, which hinders the growth of grains during the sintering process, thereby retaining a large amount of nanocrystals and ultrafine grains in the sintered blank, and some grains grow into coarse grains through secondary recrystallization, thus presenting a multi-peak grain heterogeneous structure composed of nanocrystals, ultrafine grains, and coarse grains. Through the comprehensive effects of heterogeneous deformation induced strengthening, fine grain strengthening, and dispersion strengthening, the tensile strength of the molybdenum alloy is increased by about 50%, and the elongation is increased by about 77%, achieving a synergistic improvement in the strength and plasticity of the molybdenum alloy.

[0026] Beneficial effects of the present invention:

[0027] The present invention adopts ball milling and pressureless sintering preparation methods to prepare heterogeneous structure high-strength and tough molybdenum alloy. By adjusting the grinding parameters and the carbide ratio, the microstructure of the molybdenum alloy can be well regulated, thereby synergistically improving the strength and plasticity of the molybdenum alloy. However, there is currently no public report on the study of heterogeneous structure to improve the mechanical properties of molybdenum alloy. In addition, the molybdenum alloy provided by the present invention has a simple preparation process, good repeatability of microstructure and mechanical properties, simple raw materials and process flow, controllable cost, and is suitable for industrial mass production, with good economic benefits and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The XRD diagrams of the mixed powders in Example 1, Example 2, Example 3 and Comparative Example 2 are shown;

[0029] Figure 2 The microstructure diagrams of the molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2;

[0030] Figure 3 Room temperature tensile curves of molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2;

[0031] Figure 4 The inverse pole figures of the macroscopic region and the fine grain region of the molybdenum alloy prepared in Example 1;

[0032] Figure 5 The fracture morphologies of the molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific examples of the present invention.

[0034] In the following examples, the molybdenum powder used as raw material is industrial molybdenum powder, and the ball milling jar and ball milling medium of the ball milling process are both made of WC material.

[0035] Example 1

[0036] Weigh 99g of molybdenum powder and 1g of hafnium carbide powder respectively into a mixing bottle, put it into a drum mixer for mixing for 24h, and then take out the powder. Put the mixed powder into a ball mill, evacuate it for half an hour, and then introduce argon gas, then put the ball mill into a planetary ball mill for ball milling. After the ball milling is completed, take out the powder in a glove box filled with argon gas.

[0037] Among them, the ball-to-material ratio is 10:1, the ball milling speed is 300 rpm, and the ball milling time is 24 h.

[0038] The mixed powder was poured into a mold for pressing at a pressure of 200 MPa and a holding time of 120 seconds. Then it was placed in a high-temperature sintering furnace and heated to 1100°C at a rate of 10°C / min and kept for 2 hours, then heated to 1900°C at a rate of 8°C / min and kept for 2 hours, and then cooled to room temperature at a rate of 8°C / min to obtain a high-strength and tough molybdenum alloy.

[0039] The relative density of the obtained molybdenum alloy is 98.3%, the micro-Vickers hardness of the fine grain zone is 236.4HV, the micro-Vickers hardness of the coarse grain zone is 162HV, the tensile strength is 608MPa, and the elongation at break is 62.2%, showing good strength and toughness. The ultrafine grain size of the obtained molybdenum alloy is 0.3 to 2 microns, accounting for about 24%; the fine grain size is 2 to 6 microns, accounting for about 47%; the coarse grain size is 6 to 50 microns, accounting for about 19%.

[0040] Figure 4 This is the macroscopic IPF image and the enlarged image of the fine grain area of ​​the high-strength and toughness molybdenum alloy prepared in this embodiment.

[0041] Example 2

[0042] Weigh 99g of molybdenum powder and 1g of hafnium carbide powder respectively into a mixing bottle, put it into a drum mixer device for mixing for 24 hours, and then take out the powder. Put the once mixed powder into a ball mill, evacuate it for half an hour, and then pass argon gas into the ball mill. Then put the ball mill into a planetary ball mill for ball milling. After the ball milling is completed, take out the powder in a glove box filled with argon. Finally, press and sinter the mixed powder.

[0043] The ball-to-material ratio was 10:1, the ball milling speed was 400 rpm, and the ball milling time was 24 h. The pressing pressure and sintering procedure were the same as those in Example 1.

[0044] The relative density of the obtained molybdenum alloy is 99%, the micro-Vickers hardness of the fine grain area is 244.3HV, and the micro-Vickers hardness of the coarse grain area is 186.3HV. The ultrafine grain size of the obtained molybdenum alloy is 0.3 to 2 microns, accounting for about 18%; the fine grain size is 2 to 6 microns, accounting for about 44%; the coarse grain size is 6 to 50 microns, accounting for 38%.

[0045] Example 3

[0046] Weigh 99g of molybdenum powder and 1g of zirconium carbide powder respectively into a mixing bottle, put it into a drum mixer device to mix for 24 hours, and then take out the powder. Put the once mixed powder into a ball mill, evacuate it for half an hour, and then pass argon gas into the ball mill. Then put the ball mill into a planetary ball mill for ball milling. After the ball milling is completed, take out the powder in a glove box filled with argon. Finally, press and sinter the mixed powder.

[0047] The ball-to-material ratio was 10:1, the ball milling speed was 400 rpm, and the ball milling time was 12 h. The pressing pressure and sintering procedure were the same as those in Example 1.

[0048] The relative density of the obtained molybdenum alloy is 98.5%, the micro-Vickers hardness of the fine grain area is 255HV, and the micro-Vickers hardness of the coarse grain area is 185.8HV. The ultrafine grain size of the obtained molybdenum alloy is 0.3 to 2 microns, accounting for about 35%; the fine grain size is 2 to 6 microns, accounting for about 35%; the coarse grain size is 6 to 50 microns, accounting for about 30%.

[0049] Comparative Example 1

[0050] 99 g of molybdenum powder and 1 g of hafnium carbide powder were weighed and placed in a mixing bottle, which was placed in a drum mixer for mixing for 24 hours, and then the powder was taken out. Finally, the mixed powder was pressed and sintered. The pressing pressure and sintering procedure were the same as those in Example 1.

[0051] The obtained molybdenum alloy has a relative density of 92.62%, a Vickers hardness of 144 HV, and a grain size of about 27.7 microns.

[0052] Comparative Example 2

[0053] Weigh 99g of molybdenum powder and 1g of hafnium carbide powder respectively into a mixing bottle, put it into a drum mixer for mixing for 24h, and then take out the powder. Put the mixed powder into a ball mill, evacuate it for half an hour, then pass argon gas into the ball mill, and then put the ball mill into a planetary ball mill for ball milling. After the ball milling is completed, take out the powder in a glove box filled with argon gas.

[0054] The ball-to-material ratio was 10:1, the ball milling speed was 600 rpm, and the ball milling time was 24 h. The pressing pressure and sintering procedure were the same as those in Example 1.

[0055] The obtained molybdenum alloy has a relative density of 99%, a Vickers hardness of 172 HV, and a grain size of about 121.3 μm.

[0056] Figure 1 The XRD diagrams of the mixed powders in Example 1, Example 2, Example 3 and Comparative Example 2 are shown.

[0057] Figure 2 The microstructure diagrams of the molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 2 It can be seen that the molybdenum alloy prepared in Example 1 presents an obvious bimodal grain structure morphology; the molybdenum alloys prepared in Examples 2 to 3 present an obvious multimodal grain heterogeneous structure morphology; the molybdenum alloy prepared in Comparative Example 1 presents a uniform grain structure; and the molybdenum alloy prepared in Comparative Example 2 presents uniform coarse crystals.

[0058] Figure 3 is the room temperature tensile curve of the molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2; Figure 3It can be seen from the curve that the molybdenum alloy prepared in Example 1 has a tensile strength of 608 MPa and an elongation at break of 62.2%; the molybdenum alloy prepared in Example 2 has a tensile strength of 602 MPa and an elongation at break of 53.3%, showing good strength and toughness; the molybdenum alloy prepared in Example 3 has a tensile strength of 622.5 MPa and an elongation at break of 49.7%, showing good strength and toughness; the molybdenum alloy prepared in Comparative Example 1 has a tensile strength of 487.5 MPa and an elongation at break of 25.3%, showing poor comprehensive performance; the molybdenum alloy prepared in Comparative Example 2 has a tensile strength of 486.1 MPa and an elongation at break of 15.2%, showing poor comprehensive performance.

[0059] Figure 5 The following are the fracture morphologies of the molybdenum alloys prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2. Figure 5 It can be seen that for the molybdenum alloys prepared in Examples 1 to 2, the river patterns mainly exist in the coarse grains, while the fine grain area presents a mixed mode of dimple fracture, transgranular fracture and a small amount of intergranular fracture. The fracture plasticity of the sample is improved by combining the three fracture modes; the fracture of the molybdenum alloy prepared in Example 3 presents a mixed mode of transgranular fracture and intergranular fracture; the fracture of the molybdenum alloy prepared in Comparative Example 1 presents a mixed mode of obvious transgranular fracture and intergranular fracture; the fracture of the molybdenum alloy prepared in Comparative Example 2 presents a transgranular fracture mode.

Claims

1. A multi-peak grain heterogeneous structure high strength and toughness molybdenum alloy, characterized in that: By weight percentage, it includes the following components: Molybdenum: 98-99.5%, carbide: 0.5-1.5%.

2. The multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 1, characterized in that: In the multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy, the ultrafine grain size is 0.2 to 2 microns, the fine grain size is 2 to 6 microns, and the coarse grain size is 6 to 50 microns.

3. The multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 1, characterized in that: The heterogeneous structure high-strength and toughness molybdenum alloy has a relative density of 98-99%, a micro-Vickers hardness of 150-300 HV, a tensile strength of 588-638 MPa, and a strain of 30-65%.

4. A method for preparing a multimodal grain heterogeneous structure high-strength and toughness molybdenum alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Weigh molybdenum powder and carbide powder according to a preset ratio, mix and ball-mill to obtain a mixed powder; S2. The mixed powder obtained in step S1 is pressed to obtain a compact; S3. The compact obtained in step S2 is placed in a sintering furnace for sintering. After sintering, the compact is cooled to room temperature in the furnace to obtain the multi-peak grain heterogeneous structure high-strength and toughness molybdenum alloy.

5. The method for preparing a multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 4, characterized in that: The carbide is one or more of titanium carbide, zirconium carbide and hafnium carbide.

6. The method for preparing a multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 4, characterized in that: In step S1, a drum mixer is used for mixing, the mixer speed is 110 to 130 r / min, and the mixing time is 12 to 28 hours.

7. The method for preparing a multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 4, characterized in that: In step S1, a planetary ball mill is used for ball milling, the ball-to-material ratio of the ball milling is (8-15):1, the ball milling speed is 200-500 r / min, the ball milling time is 12-48 h, and the ball milling atmosphere is an inert gas.

8. The method for preparing a multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 7, characterized in that: The ball milling process uses WC carbide pots and the ball milling medium is WC carbide balls.

9. The method for preparing a multi-modal grain heterogeneous structure high-strength and tough molybdenum alloy according to claim 4, characterized in that: In step S2, the pressing pressure is 150-250 MPa and the pressing time is 60-120 s.

10. The method for preparing a multi-modal grain heterogeneous structure high-strength and toughness molybdenum alloy according to claim 4, characterized in that: In step S3, the sintering process is: in a hydrogen atmosphere, first heat up to 1000-1100°C, keep warm for 1.5-2.5h, then heat up to 1700-1900°C, keep warm for 1-2h, after the heat preservation, cool down to 500°C, and then cool to room temperature with the furnace; during the sintering process, heat up and cool down at a rate of 8-10°C / min.

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