A cobalt-reinforced W-Ni3Al alloy and its preparation method

Abstract

The present invention provides a method for preparing a cobalt-reinforced W-Ni3Al alloy, comprising the following steps: subjecting Ni3Al powder to high-energy ball milling, drying and sieving to obtain flaky Ni3Al powder; mixing tungsten powder, cobalt powder and the flaky Ni3Al powder to obtain a composite raw material powder; and sintering the composite raw material powder to obtain a cobalt-reinforced W-Ni3Al alloy. The present invention uses a small amount of cobalt powder as an additive and prepares a cobalt-reinforced W-Ni3Al alloy through high-energy ball milling and rapid sintering, which has the characteristics of low raw material cost, simple and efficient process, etc.; the results show that the method provided by the present invention can prepare a fine-grained tungsten alloy with excellent mechanical properties at a temperature lower than the melting point temperature of the binder phase Ni3Al.

Description

Technical Field

[0001] The present invention relates to the technical field of tungsten alloys and their preparation, and particularly relates to a cobalt-reinforced W-Ni3Al alloy and a preparation method thereof. Background Art

[0002] Tungsten alloys are used in fields such as oil drilling, aerospace, medical, and national defense due to their high density, high strength, high melting point, good wear resistance, good workability, and high radiation absorption. Especially in the field of national defense, compared with depleted uranium alloy armor-piercing projectiles, tungsten alloys as the core material of armor-piercing projectiles have the advantage of being environmentally friendly. However, for the currently used W-Ni-Fe alloy, which is the core material of tungsten alloy armor-piercing projectiles, due to its insensitivity to adiabatic shear, it is easy to form a mushroom head during the armor-piercing process, resulting in a reduction in armor-piercing penetration ability. Generally speaking, the adiabatic shear effect is closely related to the strength, hardness, thermal conductivity, and grain size of the material. Specifically, materials with higher strength, greater hardness, finer tungsten grains, and lower thermal conductivity are more likely to form adiabatic shear bands and thus exhibit excellent armor-piercing ability. The Ni3Al intermetallic compound has a thermal conductivity similar to that of depleted uranium alloy and a lower thermal diffusivity, indicating that it has an adiabatic shear property similar to that of depleted uranium alloy. At the same time, the yield strength of Ni3Al has a positive temperature effect below the peak temperature, and the material rapidly softens when the temperature exceeds the peak temperature. This effect helps to initiate thermal shear behavior. When used as the armor-piercing warhead, it has self-sharpening and does not reduce its penetration depth. Therefore, the W-Ni3Al alloy has certain competitiveness in the manufacture of kinetic energy armor-piercing projectiles. However, the currently prepared W-Ni3Al alloy has low strength and hardness and large tungsten grain size, which far from meets the requirements of kinetic energy penetrators for the performance of tungsten alloys. Therefore, how to prepare a fine-grained W-Ni3Al alloy with excellent comprehensive mechanical properties is an important topic facing researchers.

[0003] In order to meet the application requirements of high-performance tungsten alloys in advanced civilian industries and national defense industries and other cutting-edge fields, domestic and foreign research scholars are committed to improving the performance of tungsten alloys by developing new technologies, especially strengthening technologies, such as enhanced auxiliary sintering, strain strengthening, and subsequent heat treatment. At present, these technologies all focus on single strengthening means. At the same time, compared with the above-mentioned many strengthening methods, adding alloying elements is a simple and effective method, especially the addition of trace alloying elements. Currently, the most studied is the use of rare earth alloying to improve the performance of tungsten alloys, but the low availability and high cost of rare earth elements limit their application. Therefore, it is very necessary to study the selection of other alloying elements for trace addition to tungsten alloys, which can produce multiple coupling strengthening effects and can significantly improve the mechanical properties of tungsten alloys without subsequent heat treatment, so as to reduce raw material costs and energy consumption. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a preparation method of cobalt-reinforced W-Ni3Al alloy. The tungsten alloy prepared in this application has the advantages of fine tungsten grains, high relative density, high strength and hardness, etc. The comprehensive mechanical properties of the alloy have been significantly improved compared with previous studies.

[0005] In view of this, this application provides a preparation method of cobalt-reinforced W-Ni3Al alloy, including the following steps:

[0006] a) High-energy ball milling of Ni3Al powder, drying and sieving to obtain flaky Ni3Al powder;

[0007] b) Mixing tungsten powder, cobalt powder and the flaky Ni3Al powder to obtain a uniformly mixed composite raw material powder;

[0008] c) Rapid sintering of the composite raw material powder to obtain cobalt-reinforced W-Ni3Al alloy.

[0009] Preferably, in the composite raw material powder, the content of tungsten powder is 83.5-95 wt%, the content of cobalt powder is 0.1-1.5 wt%, and the content of flaky Ni3Al powder is 4.9-15 wt%.

[0010] Preferably, the high-energy ball milling is specifically: first, low-speed ball milling is carried out at a speed below 300 r / min for 1-15 h, and then high-speed ball milling is carried out at a speed above 300 r / min for 0.5-10 h in two-step ball milling.

[0011] Preferably, the weight ratio of balls to materials in the high-energy ball milling is 5-30:1.

[0012] Preferably, the control agent for the high-energy ball milling is selected from one or more of stearic acid, sodium chloride, and absolute ethanol. The high-energy ball milling is carried out under a protective atmosphere, and the protective atmosphere is argon or nitrogen.

[0013] Preferably, the mesh number of the sieve for sieving is 800-2800 meshes.

[0014] Preferably, the mixing is to put tungsten powder, cobalt powder, the flaky Ni3Al powder and grinding balls into a ball milling tank, without adding grinding balls or the ball-to-material ratio not exceeding 5:1, and mixing for 2-12 h at a speed not exceeding 400 r / min.

[0015] Preferably, the sintering adopts the spark plasma sintering method. The sintering temperature of the spark plasma sintering method is 1150-1300 °C, the sintering pressure is 30-50 MPa, the heating rate is 50-300 °C / min, the holding time is 1-30 min, and the sintering vacuum degree < 30 Pa.

[0016] Preferably, the average particle size of the Ni3Al powder is ≤40 μm, and the purity is ≥99%; the average particle size of the tungsten powder is ≤4 μm, and the purity is ≥99%; the average particle size of the cobalt powder is ≤1 μm, and the purity is ≥99%.

[0017] This application also provides a cobalt-reinforced W-Ni3Al alloy, which is the cobalt-reinforced W-Ni3Al alloy prepared by the above-mentioned preparation method.

[0018] The present invention provides a preparation method of a cobalt-reinforced W-Ni3Al alloy. First, flaky Ni3Al powder is prepared by high-energy ball milling. Next, through mixing, a uniform composite raw material powder containing tungsten powder, flaky Ni3Al powder and cobalt powder is obtained; finally, the composite raw material powder is sintered to obtain a cobalt-reinforced fine-grained W-Ni3Al alloy. In the preparation method of the cobalt-reinforced W-Ni3Al alloy provided by the present invention, the addition amount of cobalt powder is very small, the sintering temperature is low, and the sintering time is short. Therefore, compared with the conventional method, the comprehensive preparation cost of the alloy is low. During the pretreatment of the binder phase Ni3Al by high-energy ball milling in the present invention, while the powder gradually changes from near-spherical to flaky, a large number of vacancies and dislocations and other defects can also be introduced into the powder. These are not only beneficial to the low-temperature densification sintering of the subsequent tungsten alloy, but also beneficial to the interdiffusion between cobalt elements and the binder phase during the subsequent sintering process to form a (Ni,Co)3Al4 solid solution phase. For the addition of trace cobalt elements, on the one hand, the presence of cobalt in the alloy leads to the formation of a (Ni,Co)3Al4 solid solution phase, which can perform solid solution strengthening on the alloy; on the other hand, a Co3(Al,W) precipitation phase is also formed between cobalt, tungsten and aluminum, which can perform precipitation strengthening on the alloy. In addition, the in-situ generated Al2O3 phase during the preparation process can perform oxide dispersion strengthening on the alloy. Therefore, under a variety of coupled strengthening mechanisms, the prepared W-Ni3Al alloy with trace cobalt addition exhibits excellent strength and hardness at room temperature.

[0019] Furthermore, this application preferably adopts the spark plasma sintering method. During the spark plasma sintering process, the high heating rate can promote the densification of the alloy to be completed in a short time, and the grain coarsening caused by surface diffusion is minimized, thereby suppressing the growth of grains, making the grains of the tungsten alloy finer, which is beneficial to improving the mechanical properties of the tungsten alloy. Description of the Drawings

[0020] Figure 1 It is the morphology diagram (a) of the high-energy ball milled Ni3Al powder and the statistical chart (b) of the flake thickness size in Example 1 of the present invention;

[0021] Figure 2 It is the XRD diagram of the cobalt-reinforced W-Ni3Al alloy prepared in Example 1 of the present invention;

[0022] Figure 3 Surface electron backscattering SEM image (a) and tungsten grain size statistical chart (b) of the cobalt-reinforced W-Ni3Al alloy prepared in Example 1 of the present invention. Detailed implementation manners

[0023] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0024] In view of the problems that the strength and hardness of the W-Ni3Al alloy obtained by conventional preparation are low and the improvement means are limited, the present application provides a preparation method of a trace cobalt-reinforced W-Ni3Al alloy. First, Ni3Al is pretreated by high-energy ball milling to obtain flaky Ni3Al. In this process, while the powder gradually changes from near-spherical to flaky, a large number of vacancies and dislocations and other defects can also be introduced into the powder. These are not only beneficial to the lower-temperature densification sintering of the subsequent tungsten alloy, but also beneficial to the interdiffusion between cobalt elements and the binder phase during the subsequent sintering process to form a (Ni,Co)3Al4 solid solution phase. Secondly, by adding trace cobalt to the raw materials and through the cooperation of multiple factors during the preparation process, various coupling strengthening effects are generated, and finally a fine-grained tungsten alloy with high density and excellent strength and hardness is prepared at a lower sintering temperature. Specifically, the present application provides a preparation method of a cobalt-reinforced W-Ni3Al alloy, including the following steps:

[0025] Perform high-energy ball milling on the Ni3Al powder, dry it and then screen it to obtain flaky Ni3Al powder;

[0026] Mix the tungsten powder, cobalt powder and the flaky Ni3Al powder to obtain a composite raw material powder;

[0027] Sinter the composite raw material powder to obtain a cobalt-reinforced W-Ni3Al alloy.

[0028] In the present invention, Ni3Al powder was first pretreated, that is, Ni3Al powder was subjected to high-energy ball milling with a slow-first and then-fast speed to obtain flaky powder; the ball milling method of slow-first and then-fast speed was a two-step ball milling, which was first low-speed ball milling at a speed below 300 r / min for 1 to 15 h, and then high-speed ball milling at a speed above 300 r / min for 0.5 to 10 h; more preferably, it was a two-step ball milling of first low-speed ball milling at a speed of 150 r / min to 200 r / min for 6 to 10 h, and then high-speed ball milling at a speed above 300 r / min to 400 r / min for 1 to 4 h. The ball-to-powder weight ratio in the high-energy ball milling process was 5 to 30:1. In the present invention, the grinding media selected in the high-energy ball milling process were one or more of stearic acid, sodium chloride, and absolute ethanol, wherein the mass percentage of stearic acid was 0.1 to 1 wt%; more preferably, the mass percentage of 0.5 to 0.7 wt% of sodium chloride was 2 to 10 wt%, more preferably 5 to 10 wt%; the mass percentage of absolute ethanol was ≤15 wt%, more preferably 10 to 15 wt%. In the present invention, the protective atmosphere selected in the high-energy ball milling process was argon or nitrogen

[0029] In the present invention, after high-energy ball milling, the flaky Ni3Al powder was dried, and after complete drying, it was sieved with a sieve to obtain flaky Ni3Al powder with relatively uniform particle size; the mesh number of the sieve selected was 800 to 2800 meshes, more preferably the mesh number of the sieve was 800 to 2000 meshes.

[0030] In the present invention, then the obtained flaky Ni3Al powder was mixed with tungsten powder and cobalt powder according to a certain mass ratio to obtain a composite powder; in this application, the content of the tungsten powder was 83.5 to 95 wt%, the content of the Ni3Al powder was 4.9 to 15 wt%, and the content of the cobalt powder was 0.1 to 1.5 wt%; more preferably, the content of the tungsten powder was 84 to 93.5 wt%, the content of the Ni3Al powder was 6 to 15 wt%, and the content of the cobalt powder was 0.5 to 1 wt%.

[0031] In the present invention, the mixing process can be specifically carried out with or without adding grinding balls.

[0032] The mixing with adding grinding balls was specifically as follows: tungsten powder, the flaky Ni3Al powder, cobalt powder, and grinding balls were put into a ball mill jar, and mixed at a ball-to-powder ratio not exceeding 5:1 and a speed not exceeding 400 r / min for 2 to 12 h.

[0033] The mixing method without adding grinding balls was specifically as follows: tungsten powder, the flaky Ni3Al powder, and cobalt powder were put into a ball mill jar, and mixed at a speed not exceeding 400 r / min for 2 to 12 h.

[0034] In the present invention, finally, the obtained composite raw material powder is sintered in a spark plasma sintering furnace system to obtain a cobalt-reinforced W-Ni3Al alloy. The spark plasma sintering is a one-step sintering process with a sintering temperature of 1150 - 1300 °C, a sintering pressure of 30 - 50 MPa, a heating rate of 50 - 300 °C / min, a holding time of 1 - 30 min, and a sintering vacuum degree of < 30 Pa.

[0035] The present invention also provides a tungsten alloy prepared by the preparation method described in the above technical solution.

[0036] In the present application, first, Ni3Al is pretreated by high-energy ball milling technology. In this process, while the powder gradually changes from nearly spherical to flaky, a large number of vacancies and dislocations and other defects can also be introduced into the powder. These are not only beneficial to the lower-temperature densification sintering of the subsequent tungsten alloy but also conducive to the interdiffusion between cobalt elements and the binder phase during the subsequent sintering process to form a (Ni,Co)3Al4 solid solution phase. Then, the flaky Ni3Al powder is mixed with tungsten powder and cobalt powder, and finally, a high-performance cobalt-reinforced W-Ni3Al alloy is prepared by spark plasma sintering. Regarding the addition of cobalt elements, on the one hand, the presence of cobalt in the alloy leads to the formation of a (Ni,Co)3Al4 solid solution phase, which can perform solid solution strengthening on the alloy; on the other hand, a Co3(Al,W) precipitation phase is also formed between cobalt, tungsten, nickel, and aluminum, which can perform precipitation strengthening on the alloy. In addition, the Al2O3 phase formed by in-situ oxidation during the preparation process can also perform oxide dispersion strengthening on the alloy. Therefore, under various coupled strengthening mechanisms, the prepared cobalt-added W-Ni3Al alloy has excellent strength and hardness at room temperature. Moreover, the content of cobalt powder used in the present invention is relatively low, and the sintering temperature is relatively low, which can reduce raw material costs and energy consumption. Using one or more of stearic acid, sodium chloride, and absolute ethanol as the grinding medium for high-energy ball milling can not only reduce the powder agglomeration state and improve the uniformity of particle size distribution but also has the characteristics of being easily separated from the raw material powder and high production efficiency. Further, the use of spark plasma technology can sinter materials at a lower temperature and in a shorter cycle than other sintering methods. During the spark plasma sintering process, a high heating rate can promote the densification of the alloy in a shorter time, and the grain coarsening caused by surface diffusion is minimized, thereby suppressing the growth of grains and also being beneficial to improving the mechanical properties of the tungsten alloy.

[0037] In summary, the present invention is a low-cost, simple, fast, and efficient preparation method for W-Ni3Al alloys, and it also has reference significance for the preparation of other powder metallurgy materials.

[0038] To better understand the present invention, the following examples are used to describe in detail the preparation method of the cobalt-reinforced W-Ni3Al alloy provided by the present invention. The protection scope of the present invention is not limited by the following examples.

[0039] Example 1

[0040] A method for preparing a cobalt-enhanced W-Ni3Al alloy in this embodiment includes the following steps and process conditions:

[0041] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and performing two-step ball milling on a high-energy ball mill, wherein the ball milling medium is anhydrous ethanol, the mass percentage is ≤15wt%, the ball-to-material ratio is 20:1, and the ball milling atmosphere is argon; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200r / min for 10h, and then performing high-speed ball milling at 310r / min for 2h to obtain flaky Ni3Al powder, and then sieving with a 1000-mesh screen to obtain flaky Ni3Al powder with uniform particle size;

[0042] b) preparing the materials according to the mass percentage of W 90wt%, sieved Ni3Al 9wt%, and Co 1wt%, adding grinding balls with a ball-to-material ratio of 5:1, and ball milling and mixing at a speed of 300r / min for 6h to obtain a uniform and fine composite powder;

[0043] c) After the composite powder is loaded into a graphite mold, it is placed in a heating chamber of a spark plasma sintering system, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1250℃, the holding time is 5min, and the sintering vacuum degree is less than 30Pa;

[0044] Through the above preparation method, a W-9Ni3Al-1Co alloy with uniform structure is obtained, wherein the average tungsten grain size is less than 3.7 μm, the relative density is greater than 98%, the macroscopic hardness is 71 HRA, and the bending strength is 1545.97 MPa.

[0045] The high energy ball milled Ni3Al powder and the obtained tungsten alloy were characterized. The results are shown in Figure 1 , Figure 2 and Figure 3 . Figure 1 The morphology diagram (a) and the flake thickness size statistics diagram (b) of the high-energy ball-milled Ni3Al powder in Example 1 show that the Ni3Al powder undergoes large plastic deformation during the high-energy ball milling process and becomes a flake powder with an average thickness of less than 3 μm. Figure 2 This is the XRD diagram of the tungsten alloy obtained in Example 1. From the figure, we can see two main phases, W and Ni3Al, and three strengthening phases, (Ni,Co)3Al4, Co3(Al,W), and Al2O3. Figure 3 a is a surface electron backscattering SEM image of the tungsten alloy obtained in Example 1, in which various phases are evenly distributed and the Al2O3 phase is located at the interface between the tungsten phase and the bonding phase. Figure 3b is a statistical diagram of the grain size of the tungsten alloy obtained in Example 1. It can be seen from the figure that the obtained cobalt-reinforced fine-grained W-Ni3Al alloy has a uniform structure and no obvious defects such as pores.

[0046] Example 2

[0047] This embodiment provides a method for preparing a cobalt-enhanced W-Ni3Al alloy, comprising the following steps and process conditions:

[0048] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and performing two-step ball milling on a high-energy ball mill, wherein the ball milling medium is anhydrous ethanol, the mass percentage is ≤15wt%, the ball-to-material ratio is 20:1, and the ball milling atmosphere is argon; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200r / min for 10h, and then performing high-speed ball milling at 310r / min for 2h to obtain flaky Ni3Al powder, and then sieving with a 1000-mesh screen to obtain flaky Ni3Al powder with uniform particle size;

[0049] b) preparing the materials in the mass percentage of W 90wt%, sieved Ni3Al 9wt%, and Co 1wt%, adding grinding balls with a ball-to-material ratio of 5:1, and ball milling at a speed of 300 r / min for 6 hours to obtain a uniform and fine composite powder;

[0050] c) After the composite powder is loaded into a graphite mold, it is placed in a heating chamber of a spark plasma sintering system, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1300℃, the holding time is 5min, and the sintering vacuum degree is less than 30Pa;

[0051] Through the above preparation method, a W-9Ni3Al-1Co alloy with uniform structure is obtained, wherein the average tungsten grain size is less than 4 μm, the relative density is greater than 99%, the macroscopic hardness is 70.4 HRA, and the bending strength is 1397.76 MPa.

[0052] Example 3

[0053] This embodiment provides a method for preparing a cobalt-enhanced W-Ni3Al alloy, comprising the following steps and process conditions:

[0054] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and performing two-step grinding on a high-energy ball mill, wherein the ball milling medium is NaCl, the mass percentage is 5wt%, the ball-to-material ratio is 10:1, and the ball milling atmosphere is argon; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200 r / min for 10 hours, and then performing high-speed ball milling at 360 r / min for 2 hours to obtain flaky Ni3Al powder, and then sieving with a 1000-mesh screen to obtain flaky Ni3Al powder with uniform particle size;

[0055] b) mixing the materials according to the mass percentage of W 90wt%, sieved Ni3Al 9.5wt%, and Co 0.5wt%, adding grinding balls with a ball-to-material ratio of 5:1, and ball milling at a speed of 300r / min for 6h to obtain a uniform and fine composite powder;

[0056] c) After the composite powder is loaded into a graphite mold, it is placed in a spark plasma sintering system heating chamber, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1250℃, the holding time is 5min, and the sintering vacuum degree is <30Pa;

[0057] Through the above preparation method, a W-9.5Ni3Al-0.5Co alloy with uniform structure is obtained, wherein the average tungsten grain is less than 4 μm, the relative density is greater than 97%, the macroscopic hardness is 72.2 HRA, and the bending strength is 1256.72 MPa.

[0058] Example 4

[0059] This embodiment provides a method for preparing a cobalt-enhanced W-Ni3Al alloy, comprising the following steps and process conditions:

[0060] a) weighing a certain amount of Ni3Al powder and loading it into a ball milling jar, and performing two-step ball milling on a high-energy ball mill, wherein the ball milling medium is stearic acid, the mass percentage is 0.7wt%, the ball-to-material ratio is 10:1, and the ball milling atmosphere is argon; the ball milling process is firstly low-speed ball milling at a rotation speed of 200 r / min for 6 hours, and then high-speed ball milling at 380 r / min for 3 hours to obtain flaky Ni3Al powder; and then sieving with a 2000 mesh screen to obtain flaky Ni3Al powder with uniform particle size;

[0061] b) mixing the materials according to the mass percentage of W 85wt%, sieved Ni3Al 14.3wt%, and Co 0.7wt%, without adding grinding balls, and mixing at a speed of 350r / min for 6h to obtain a uniform and fine composite powder;

[0062] c) After the composite powder is loaded into a graphite mold, it is placed in a heating chamber of a spark plasma sintering system, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1300℃, the holding time is 5min, and the sintering vacuum degree is less than 30Pa;

[0063] Through the above preparation method, a W-14.3Ni3Al-0.7Co alloy with uniform structure is obtained, wherein the average tungsten grain size is less than 4.2 μm, the relative density is greater than 97%, the macroscopic hardness is 72.5 HRA, and the bending strength is 1246.34 MPa.

[0064] Example 5

[0065] This embodiment provides a method for preparing a cobalt-enhanced W-Ni3Al alloy, comprising the following steps and process conditions:

[0066] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and then performing two-step ball milling on a high-energy ball mill, wherein the ball milling medium is NaCl, the mass percentage is 5wt%, the ball-to-material ratio is 20:1, and the ball milling atmosphere is argon; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200r / min for 6h, and then performing high-speed ball milling at 360r / min for 2h to obtain flaky Ni3Al powder; sieving with an 800-mesh screen to obtain flaky Ni3Al powder with uniform particle size;

[0067] b) mixing the materials according to the mass percentage of W 93wt%, sieved Ni3Al 6wt%, and Co 1wt%, without adding grinding balls, and mixing at a speed of 300r / min for 6h to obtain a uniform and fine composite powder;

[0068] c) After the composite powder is loaded into a graphite mold, it is placed in a spark plasma sintering system heating chamber, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1200℃, the holding time is 5min, and the sintering vacuum degree is less than 30Pa;

[0069] Through the above preparation method, a W-6Ni3Al-1Co alloy with uniform structure is obtained, wherein the average tungsten grain size is less than 3.5 μm, the relative density is greater than 96%, the macroscopic hardness is 74.2 HRA, and the bending strength is 1218.76 MPa.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing a W-Ni3Al alloy without cobalt element, comprising the following steps and process conditions:

[0072] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and performing two-step ball milling on a high-energy ball mill, wherein the ball milling medium is NaCl, the mass percentage is 5wt%, the ball-to-material ratio is 10:1, and the ball milling atmosphere is argon; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200 r / min for 10 hours, and then performing high-speed ball milling at 360 r / min for 2 hours to obtain flaky Ni3Al powder; sieving with an 800-mesh sieve to obtain flaky Ni3Al powder with uniform particle size;

[0073] b) mixing the materials according to the mass percentage of W 90wt%, sieved Ni3Al 10wt%, adding grinding balls with a ball-to-material ratio of 5:1, and ball milling at a speed of 300r / min for 6h to obtain a uniform and fine composite powder;

[0074] c) After the composite powder is loaded into a graphite mold, it is placed in a spark plasma sintering system heating chamber, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1300℃, the holding time is 5min, and the sintering vacuum is less than 30Pa;

[0075] Through the above preparation method, W-10Ni3Al alloy is obtained. Although the average tungsten grain size of the alloy is less than 4.5 μm, the presence of pores in the alloy leads to a lower relative density. The macroscopic hardness of the alloy is 68.3 HRA, and its bending strength is also low, only 798.72 MPa.

[0076] Comparative Example 2

[0077] This comparative example provides a method for preparing a cobalt-reinforced W-Ni3Al alloy by directly mixing the Ni3Al powder without high-energy ball milling, comprising the following steps and process conditions:

[0078] a) directly mixing Ni3Al powder, W powder and Co powder at a speed of 300 r / min for 6 h without adding grinding balls according to the weight percentage of W 90wt%, sieved Ni3Al 9wt% and Co 1wt% to obtain a uniform composite powder;

[0079] b) After the above composite powder is loaded into a graphite mold, it is placed in a heating chamber of a spark plasma sintering system, and after vacuuming, spark plasma one-step sintering is performed with a sintering pressure of 40 MPa, a heating rate of 100°C / min, a sintering temperature of 1250°C, a holding time of 5 min, and a sintering vacuum degree of <30 Pa; after the above sintering, a W-9Ni3Al-1Co alloy is obtained.

[0080] Through the above preparation method, W-9Ni3Al-1Co alloy is obtained. Although the average tungsten grain size of the alloy is less than 4.5 μm and the macroscopic hardness is 71.6 HRA, the relative density of the alloy is low and its bending strength is also low, only 970.79 MPa.

[0081] Comparative Example 3

[0082] This comparative example provides a method for preparing a W-Ni3Al alloy that does not contain cobalt and does not pre-high-energy ball mill the Ni3Al raw material, comprising the following steps and process conditions:

[0083] a) directly mixing Ni3Al powder and W powder at a speed of 300 r / min for 10 h without adding grinding balls according to the mass percentage of W 90wt% and Ni3Al 10wt% after sieving to obtain a uniform composite powder;

[0084] b) After the composite powder is loaded into a graphite mold, it is placed in a spark plasma sintering system heating chamber, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1300℃, the holding time is 5min, and the sintering vacuum degree is less than 30Pa;

[0085] By solid phase sintering below the melting point of Ni3Al (1395°C), W-10Ni3Al alloy is obtained. Although the average tungsten grains of the alloy are less than 5μm, the presence of pores in the alloy leads to a lower relative density. The macroscopic hardness of the alloy is 67.5HRA, and its bending strength is also low, only 630.42MPa.

[0086] Comparative Example 4

[0087] This comparative example provides a method for preparing a W-Ni3Al alloy with a high cobalt content, comprising the following steps and process conditions:

[0088] a) weighing a certain amount of Ni3Al powder and putting it into a ball milling jar, and performing two-step ball milling on a ball mill, wherein the ball milling medium is anhydrous ethanol, the mass percentage is ≤15wt%, and the ball-to-material ratio is 10:1; the ball milling process is firstly performing low-speed ball milling at a rotation speed of 200r / min for 10h, and then performing high-speed ball milling at 310r / min for 2h to obtain flaky Ni3Al powder; sieving with a 1000-mesh sieve to obtain flaky Ni3Al powder with uniform particle size;

[0089] b) mixing the materials according to the mass percentage of W 90wt%, sieved Ni3Al 6wt%, and Co 4wt%, adding grinding balls with a ball-to-material ratio of 5:1, and ball milling at a speed of 300r / min for 6h to obtain a uniform and fine composite powder;

[0090] c) After the composite powder is loaded into a graphite mold, it is placed in a spark plasma sintering system heating chamber, and after vacuuming, spark plasma one-step sintering is performed, the sintering pressure is 40MPa, the heating rate is 100℃ / min, the sintering temperature is 1300℃, the holding time is 5min, and the sintering vacuum is less than 30Pa;

[0091] Through the above preparation method, W-6Ni3Al-4Co alloy is obtained. Although the average tungsten grain of the alloy is less than 5μm and the macro hardness is 85.3HRA, the relative density of the alloy is low and its bending strength is also low, only 619.35MPa.

[0092] In Examples 1 to 5 of the present invention, cobalt-reinforced W-Ni3Al alloy was successfully prepared at a relatively low temperature. Moreover, the tungsten grains of the prepared tungsten alloy are fine, with an average size <4.5 μm, a relative density above 96%, a macro hardness above 70 HRA, and a flexural strength above 1218 MPa. Among them, the strength of the tungsten alloy obtained in Example 1 is as high as 1545.97 MPa. From the comparison with Comparative Example 1, it can be seen that the presence of cobalt element can not only form the (Ni,Co)3Al4 solid solution phase, but also form the Co3(Al,W) precipitation phase between tungsten and aluminum, playing a role of multiple coupling strengthening, which greatly improves the mechanical properties of the W-Ni3Al alloy. From the comparison with Comparative Example 2, it can be seen that the high-energy ball milling pretreatment of Ni3Al powder has an important influence on the properties of cobalt-reinforced W-Ni3Al alloy. While high-energy ball milling makes it gradually change from nearly spherical to flaky, it can also introduce a large number of defects such as vacancies and dislocations into the powder. These are not only beneficial to the low-temperature densification sintering of the subsequent tungsten alloy, but also beneficial to the interdiffusion between cobalt element and the binder phase during the subsequent sintering process to form the (Ni,Co)3Al4 solid solution phase. From the comparison with Comparative Example 3, it can be seen that the strength of the W-Ni3Al alloy prepared without cobalt element and without prior high-energy ball milling pretreatment of Ni3Al powder is only 630.42 MPa, which further illustrates that the addition of trace cobalt element and the high-energy ball milling pretreatment of Ni3Al powder have important influences on the preparation of high-performance W-Ni3Al alloy. From the comparison with Comparative Example 4, it can be seen that although adding too much cobalt content can greatly increase the hardness of the alloy, its flexural strength is very low.

[0093] The above description of the embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0094] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of cobalt-reinforced W-Ni3Al alloy, comprising the following steps: a) High-energy ball milling Ni3Al powder, drying and sieving it to obtain flaky Ni3Al powder; b) Mixing tungsten powder, cobalt powder and the flaky Ni3Al powder to obtain a uniformly mixed composite raw material powder; in the composite raw material powder, the content of the tungsten powder is 83.5 - 95 wt%, the content of the cobalt powder is 0.1 - 1.5 wt%, and the content of the flaky Ni3Al powder is 4.9 - 15 wt%; c) Rapidly sintering the composite raw material powder to obtain cobalt-reinforced W-Ni3Al alloy; The sintering adopts the spark plasma sintering method, the sintering temperature of the spark plasma sintering method is 1150 - 1300 °C, the sintering pressure is 30 - 50 MPa, the heating rate is 50 - 300 °C / min, the holding time is 1 - 30 min, and the sintering vacuum degree < 30 Pa.

2. The preparation method according to claim 1, characterized in that, The high-energy ball milling is specifically: first, low-speed ball milling is carried out at a speed below 300 r / min for 1 - 15 h, and then high-speed ball milling is carried out at a speed above 300 r / min for 0.5 - 10 h in two-step ball milling.

3. The preparation method according to claim 1, characterized in that The ball-to-material weight ratio of the high-energy ball milling is 5 - 30:

1.

4. The preparation method according to claim 1, wherein, The control agent for the high-energy ball milling is selected from one or more of stearic acid, sodium chloride, and absolute ethanol, and the high-energy ball milling is carried out under a protective atmosphere, and the protective atmosphere is argon or nitrogen.

5. The preparation method according to claim 1, wherein The mesh number of the sieve for sieving is 800 - 2800 mesh.

6. The preparation method according to claim 1, wherein, The mixing is to put tungsten powder, cobalt powder, the flaky Ni3Al powder and grinding balls into a ball milling tank, without adding grinding balls or the ball-to-material ratio does not exceed 5:1, and mix at a speed not exceeding 400 r / min for 2 - 12 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The average particle size of the Ni3Al powder ≤ 40 μm, the purity ≥ 99%; the average particle size of the tungsten powder ≤ 4 μm, the purity ≥ 99%; the average particle size of the cobalt powder ≤ 1 μm, the purity ≥ 99%.

8. A cobalt-reinforced W-Ni3Al alloy, which is the cobalt-reinforced W-Ni3Al alloy prepared by the preparation method according to any one of claims 1 - 7.

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