A high-density tungsten alloy and a method for manufacturing the same

Abstract

The application discloses a high-density tungsten alloy and a preparation method thereof. The tungsten alloy compact is heated to a pre-sintering temperature under vacuum, and is pressed when reaching the pre-sintering temperature, and is pre-sintered under a pressure of 15-20 MPa. After the pre-sintering is completed, the pressure is reduced to 5-15 MPa, then the temperature is increased to a solid-phase sintering temperature, and solid-phase sintering is carried out. After the solid-phase sintering is completed, the pressure is reduced to 0 MPa, then the temperature is increased to a liquid-phase sintering temperature, and liquid-phase sintering is carried out, thereby obtaining the tungsten alloy. The pre-sintering temperature is 850-950 DEG C, the solid-phase sintering temperature is 1200-1300 DEG C, and the liquid-phase sintering temperature is 1450-1500 DEG C. Through the above method, the tungsten alloy with a relative density of greater than or equal to 99.5% can be prepared.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of powder metallurgy liquid phase sintering tungsten alloy, and particularly relates to a high-density tungsten alloy and a preparation method thereof. BACKGROUND

[0002] Tungsten alloy is a kind of composite material, which is usually composed of high-strength and high-hardness tungsten particles and soft binder phase. Tungsten alloy has the remarkable characteristics of high strength (> 900 MPa), high hardness (> 400 HV), high toughness (elongation > 20%), high density (> 17 g / cm 3 ) and so on. These advantages make tungsten alloy be widely used in military and defense fields, such as bullets, cannonballs, grenades and gun components. In particular, the high-density feature makes it be regarded as the best material for armor-piercing bullets. Tungsten alloy armor-piercing bullets have extremely high kinetic energy and excellent armor-piercing ability, and can penetrate multiple layers of composite armor and large-angle armor. Compared with depleted uranium bullets, tungsten alloy armor-piercing bullets have the remarkable advantages of no radiation, no pollution and low cost.

[0003] Due to the high melting point of tungsten, the use of smelting method to prepare tungsten-based materials has coarse grains and poor performance. Therefore, the preparation of tungsten alloy usually adopts the powder metallurgy method. The powder metallurgy method for preparing tungsten alloy needs to go through the three processes of powder mixing, compaction molding and sintering. In the process of compaction molding, the compacts can only be improved to 60-65% in density by using die pressing, cold isostatic pressing and other methods. In the sintering process, a large number of pores will be produced in the compacts, so that the relative density of tungsten alloy can be effectively improved by pressing during sintering. At the same time, the sintering process will also seriously affect the performance of the tungsten alloy. The common powder metallurgy methods for tungsten alloy include spark plasma sintering, hot isostatic pressing sintering and vacuum hot pressing sintering. Among them, the spark plasma sintering can make the powder complete alloying in a short time under a large current and high pressure. However, because the liquid phase will damage the spark plasma sintering equipment, the solid phase sintering method is usually used to sinter at a lower temperature, and the performance and density of the alloy are poor. Hot isostatic pressing sintering can apply isostatic pressure at high temperature to obtain dense tungsten alloy at a lower sintering temperature. However, hot isostatic pressing sintering requires high packaging technology, and the cost of hot isostatic pressing package is high, which is difficult to be used on a large scale. Vacuum hot pressing sintering has the remarkable characteristics of low cost, high efficiency and simple equipment, and is commonly used to prepare various powder metallurgy materials. However, vacuum hot pressing sintering usually avoids the generation of liquid phase to prevent damage to the equipment and mold, which makes it only be able to use the solid phase sintering method to prepare tungsten alloy, and the alloy has low density and poor performance.

[0004] In the sintering step of the improved tungsten alloy and its preparation method (201810255013.1), the sintering of the pressed tungsten alloy in the sintering furnace is as follows: the temperature is raised to 900 DEG C at a temperature raising rate of 450 DEG C / h, and the temperature is kept at 900 DEG C for 4 h; then the temperature is raised to 1400 DEG C at a temperature raising rate of 75 DEG C / h, and the temperature is kept for 4 h, which is a solid phase sintering process; then the temperature is raised to 1440 DEG C at a temperature raising rate of 40 DEG C / h, and the temperature is kept for 1 h, which is a liquid phase sintering process; the above sintering stages are carried out under the condition of continuously supplying hydrogen; finally, the temperature is lowered to 1100 DEG C from 1440 DEG C, the hydrogen is converted into nitrogen at 1100 DEG C, and the prepared tungsten alloy is taken out from 1100 DEG C to natural temperature, thereby obtaining a 60W-28Ni-12Fe alloy. However, since no pressure is applied to the sample during the sintering process, the tungsten alloy has a low density (relative density 83-87.2%) and poor tensile strength (less than 265 MPa) and elongation (less than 2.3%). SUMMARY

[0005] In view of the problem that the powder metallurgy tungsten alloy in the prior art cannot be pressurized during vacuum hot-press sintering, and the relative density of the alloy is poor, a first object of the present application is to provide a preparation method of a high-density tungsten alloy.

[0006] A second object of the present application is to provide a high-density tungsten alloy prepared by the above preparation method.

[0007] To achieve the above objects, the present application provides the following technical solutions.

[0008] The preparation method of the high-density tungsten alloy comprises the following steps: heating the tungsten alloy compact under vacuum to a pre-sintering temperature, and pressurizing when the pre-sintering temperature is reached; pre-sintering at a pressure of 15-20 MPa; after the pre-sintering is completed, reducing the pressure to 5-15 MPa, then heating to a solid phase sintering temperature, and performing solid phase sintering; after the solid phase sintering is completed, reducing the pressure to 0 MPa, then heating to a liquid phase sintering temperature, and performing liquid phase sintering, thereby obtaining the tungsten alloy; the pre-sintering temperature is 850-950 DEG C, the solid phase sintering temperature is 1200-1300 DEG C, and the liquid phase sintering temperature is 1450-1500 DEG C.

[0009] The pressure provided in the present application is a relative pressure, and 0 MPa means normal pressure relative to the vacuum table.

[0010] The preparation method of the application adopts vacuum+hot pressing, solid-liquid phase multistage sintering method, first heating under vacuum, because the tungsten alloy compact contains a large amount of pores, the vacuum environment is helpful for the discharge of gas in the compact, the discharge of gas is helpful for the connection and contact between tungsten particles, the vacuum environment can reduce the melting point of each component in the compact, and is helpful for the formation of sintering necks between tungsten particles, then pressurization when reaching the pre-sintering temperature, pre-sintering is carried out under the pressure of 15-20 MPa, pressure sintering is carried out under pre-sintering, further promoting the formation of sintering necks between tungsten powders and the formation of tungsten skeleton in the tungsten alloy, then reducing the pressure to 5-15 MPa, and then heating to 1200-1300 DEG C for solid phase sintering, because during solid phase sintering, on the one hand, because the strength of the tungsten alloy binder phase decreases due to the increase of temperature, therefore, appropriately reducing the pressure can be helpful for the maintenance of the tungsten skeleton, on the other hand, because the strength of the tungsten alloy binder phase decreases, by applying the pressure of 5-15 MPa, the voids in the tungsten skeleton can be well filled by deformation, the density of the compact can be rapidly increased by solid phase sintering and heat preservation, finally, by reducing the pressure to 0 MPa and heating to the liquid phase sintering temperature, the elastic deformation of the binder phase can be avoided, the binder phase can be fully filled in the voids, and finally high-density tungsten alloy can be obtained through liquid phase sintering.

[0011] The preparation method of the application promotes the formation of sintering necks by pre-sintering under pressure, during the pre-sintering process, only metallurgical bonding between tungsten particles occurs, so that it is shaped in advance, thereby reducing the solid phase sintering temperature, so that the solid phase sintering can be carried out at a lower temperature of 1200-1300 DEG C in the application, and because the interval between the solid phase sintering temperature and the liquid phase sintering temperature is large, the pressure can be applied during solid phase sintering and not applied during liquid phase sintering, if the pre-sintering is not carried out under pressure, the solid phase sintering densification needs to be carried out at a higher temperature, at this time, because the temperature is close to the melting point of the gamma-(Ni, Fe) phase, thermal field fluctuation and local composition segregation of the binder phase can cause the liquid phase to appear in the compact in advance. The liquid phase appearing in advance is quickly extruded under the action of pressure, which can cause the compact to collapse and deform. At the same time, the extruded liquid phase can also react with the pressurized mold (usually graphite), which can cause the mold to be difficult to demold, and even cause the mold and even the equipment to be damaged.

[0012] During the whole preparation process of the present application, the temperature and pressure need to be effectively controlled. For example, during the pre-sintering, if the temperature is too low, the binder phase does not form stable γ-(Ni, Fe) phase through diffusion, and a large amount of nickel and iron powder still exists in the form of particles. At this time, if the pressure is too high, the particles will move and the edges of the green compact will crack and drop powder; if the pressure is too low, it is not enough to make the tungsten particles contact with each other, so as to promote the formation of sintering necks; and if the solid phase sintering temperature is too high, a large amount of tungsten particles will combine with each other to form large tungsten particles, and there are still pores between these large tungsten particles. Due to the blocking effect of the closed tungsten particles, it is difficult for the subsequent liquid phase to fill these pores, so this structure is not conducive to the subsequent densification sintering. In addition, if the solid phase sintering temperature is too high, it is not conducive to the pressurization during the solid phase sintering, and the liquid phase is not pressurized.

[0013] Preferably, the tungsten alloy green compact is obtained by mixing tungsten powder and nickel-iron-based powder and then being pressed and formed.

[0014] Further preferably, in the tungsten alloy green compact, the mass fraction of tungsten powder is 85-95%.

[0015] Further preferably, in the nickel-iron-based powder, nickel and iron are contained, and the total mass fraction of nickel and iron is ≥85%, and the mass ratio of nickel to iron is 6-8:2-4.

[0016] The sintering method of the present application is suitable for W-Ni-Fe alloy and W-Ni-Fe-Co-based alloy, but the total mass fraction of nickel and iron should be ≥85%.

[0017] Further preferably, the pressed and formed mode is die pressing or cold isostatic pressing.

[0018] Preferably, the density of the tungsten alloy green compact is ≥55%, preferably ≥60%.

[0019] Preferably, the tungsten alloy green compact is first placed in a vacuum hot-pressing sintering furnace, vacuumized, and the vacuum degree is <5×10 - 3 When the temperature reaches the pre-sintering temperature, the pressure is increased to 15-20 MPa within 5-10 min. -2

[0020] Preferably, when the temperature reaches the pre-sintering temperature, the pressure is increased to 15-20 MPa within 5-10 min.

[0021] The inventor found that slowly increasing the pressure within 5-10 min does not cause the green compact to crack, and helps the powder to deform and fill sufficiently, thereby improving the density of the tungsten alloy.

[0022] ​Preferably, the pre-sintering time is 1-1.5h.

[0023] Preferably, the pressure is reduced to 5-15MPa, preferably 5-10MPa, within 5-10min after the pre-sintering is completed.

[0024] In the present application, the solid phase sintering is performed under a pressure of 5-15MPa. During the solid phase sintering, the nickel iron in the binder phase forms a stable γ-(Ni, Fe) phase through rapid solid phase diffusion at a high temperature stage. The application of a suitable pressure can make the γ-(Ni, Fe) phase uniformly wrap the tungsten skeleton, and the voids in the tungsten skeleton can be well filled through the deformation of the γ-(Ni, Fe) phase. The density of the green body is rapidly increased through the solid phase sintering holding. Due to the high temperature stage, the strength of the tungsten alloy binder phase decreases, and therefore, the slow reduction of the pressure to 5-15MPa within 5-10min can help maintain the tungsten skeleton. If the smaller pressure is not enough to make the γ-(Ni, Fe) phase deform plastically, the high temperature can soften the γ-(Ni, Fe) phase, and at this time, the application of too high pressure can cause the collapse of the newly formed tungsten skeleton.

[0025] The inventors have found that, preferably, the temperature is increased to the solid phase sintering temperature at a rate of 5-8℃ / min, and the solid phase sintering is performed.

[0026] In the present application, the temperature is increased at a rate of 5-8℃ / min, which is helpful for the stability of the thermal field in the furnace and reduces the thermal stress caused by uneven temperature increase.

[0027] Preferably, the solid phase sintering time is 2-3h.

[0028] When the solid phase sintering is performed at 1200-1300℃, the strength of the binder phase mainly based on nickel iron decreases significantly. Through the application of a pressure of 5-15MPa, the voids in the tungsten skeleton can be well filled through deformation, and the density of the green body is rapidly increased through 2-3h of holding.

[0029] Preferably, the pressure is reduced to 0MPa within 10-20min after the solid phase sintering is completed.

[0030] The inventors have found that the reduction of the pressure to 0MPa within 10-20min can avoid the elastic deformation of the binder phase, so that it can fully fill the voids.

[0031] Preferably, the temperature is increased to the liquid phase sintering temperature at a rate of 5-8℃ / min, and the liquid phase sintering is performed. The inventors have found that the slow temperature increase at a rate of 5-8℃ / min is also helpful for the uniform heating of the sample.

[0032] Preferably, the liquid phase sintering time is 0.5-1.5h. In the present application, the final liquid phase sintering is performed at 1450-1500℃, which can realize the complete liquefaction of the nickel-iron based binder phase. Through the holding time of 0.5-1.5h during the liquid phase sintering, the tungsten particles can have sufficient time to complete the partial dissolution in the liquid phase, and meanwhile, the liquid phase also has sufficient time to further fill the small gaps between the tungsten particles through capillary action to realize densification. However, the holding time at this stage should not be too long, because the long holding time will lead to the coarsening of the structure, which is not conducive to the final performance of the alloy.

[0033] Further preferably, the liquid phase sintering temperature is 1480℃, and the liquid phase sintering time is 1h.

[0034] Preferably, after the completion of the liquid phase sintering, the temperature is first lowered to 850-950℃ at a rate of 5-10℃ / min, and then the furnace is cooled to room temperature.

[0035] Because there is a certain difference in linear expansion coefficient between tungsten and the binder phase at the high temperature stage, the temperature is lowered to 900℃ at a rate of 5-10℃ / min, which can relieve the interfacial thermal stress. Below 900℃, the tungsten particles have been completely precipitated, at which time the performance of the alloy is basically stable, and the furnace cooling after the heating is turned off can reduce the energy consumption.

[0036] The present application also provides a high-density tungsten alloy prepared by the above preparation method.

[0037] The relative density of the tungsten alloy is ≥99.5%.

[0038] Beneficial effects

[0039] The preparation method of the present application adopts the method of vacuum + hot pressing, solid-liquid phase multi-stage sintering, first heats under vacuum, and pressurizes when reaching the pre-sintering temperature, and pre-sinters at a pressure of 15-20MPa. The pressure sintering under pre-sintering can promote the formation of sintering necks between tungsten powders and the formation of tungsten skeleton in the tungsten alloy. Then the pressure is lowered to 5-15MPa, and the temperature is raised to 1200-1300℃ for solid phase sintering. Because during the solid phase sintering, on the one hand, due to the increase of temperature, the strength of the binder phase of the tungsten alloy decreases, so the appropriate reduction of pressure can help to maintain the tungsten skeleton, and on the other hand, due to the decrease of the strength of the binder phase of the tungsten alloy, the pressure is maintained, and by applying a pressure of 5-15MPa, the gaps in the tungsten skeleton can be well filled through deformation. Through the solid phase sintering holding, the green density can be rapidly increased. Finally, by lowering the pressure to 0MPa and raising the temperature to the liquid phase sintering temperature, the elastic deformation of the binder phase can be avoided, the binder phase can be fully filled in the gaps, and finally a high-density tungsten alloy can be obtained through the liquid phase sintering.

[0040] The preparation method of the application realizes the tungsten alloy vacuum hot-pressing solid-liquid phase multi-stage sintering through a pre-sintering process, a powder pre-pressing process, a solid-phase pressure sintering process, a liquid-phase sintering process and a cooling process, and the relative density of the sintered tungsten alloy reaches more than 99%. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The process flow chart of the application is shown.

[0042] Figure 2 The microstructure morphology of the tungsten alloy prepared by the method of Example 1 is shown. Figure 1 As shown in the figure, the tungsten alloy is composed of white body-centered cubic tungsten particles and black face-centered cubic binder phase, wherein the binder phase is responsible for plastic deformation, and the tungsten particles provide strength support for the alloy. No obvious hole defects are found in the alloy. The tungsten particles are spherical and dispersed in the binder phase in a fine and uniform state, and there is no obvious adhesion phenomenon between the tungsten particles. DETAILED DESCRIPTION

[0043] Example 1

[0044] The tungsten alloy compact used in this example is obtained by mixing tungsten powder and nickel-iron powder and then cold isostatic pressing. In the tungsten alloy compact, the mass ratio of tungsten powder in the tungsten alloy is 90%. In the nickel-iron powder, the mass ratio of nickel to iron is 7:3, and the density of the tungsten alloy compact is 62.5%.

[0045] A tungsten alloy vacuum hot-pressing solid-liquid phase multi-stage sintering method, comprising the following steps:

[0046] Step one: pre-sintering process.

[0047] The tungsten alloy compact after powder mixing and compression molding is placed in a vacuum hot-pressing sintering furnace. When the vacuum is reduced to 5*10 -3 Pa, the compact is heated. During the process, the vacuum degree is maintained below 1*10 -2 Pa, and the temperature is increased to 900℃ at a speed of 10℃ / min, and the temperature is maintained for 1h.

[0048] Step two: powder pre-pressing process.

[0049] When the temperature in the hot-pressing sintering reaches 900℃, the compact is subjected to a pressing operation. A pressure of 20MPa is applied to the compact, and the pressure should be slowly increased to 20MPa within 10min.

[0050] Step three: solid-phase pressure sintering process.

[0051] The pressure was slowly reduced to 10 MPa over 10 minutes, and then the furnace temperature was increased to 1300°C at a rate of 5°C / min, while the pressure was maintained at 10 MPa. Afterward, the furnace temperature was maintained at 1300°C for 3 hours.

[0052] Step 4: Liquid phase sintering process.

[0053] The pressure was reduced to 0 MPa within 20 minutes, and then the furnace temperature was increased to 1480℃ at a rate of 5℃ / min and held for 1 hour.

[0054] Step 5: Cooling and temperature reduction process.

[0055] The temperature was reduced to 900°C at a rate of 5°C / min, then the heating was turned off and the furnace was allowed to cool to room temperature.

[0056] The tungsten alloy obtained in Example 1, such as Figure 1 As shown, the tungsten alloy consists of white body-centered cubic tungsten particles and a black face-centered cubic binder phase. The binder phase is responsible for plastic deformation, while the tungsten particles provide strength support to the alloy. No obvious pore defects were observed in the alloy. The tungsten particles are all spherical and are dispersed in the binder phase in a fine and uniform manner, with no obvious adhesion between the tungsten particles.

[0057] Example 2

[0058] The tungsten alloy compact used in this embodiment is obtained by mixing tungsten powder and nickel-iron powder, followed by cold isostatic pressing. The tungsten powder accounts for 90% of the tungsten alloy in the compact by mass. The nickel-iron powder has a nickel-to-iron mass ratio of 7:3, and the compact density is 62.3%.

[0059] A vacuum hot pressing solid-liquid phase multi-stage sintering method for tungsten alloys includes the following steps:

[0060] Step 1: Pre-firing process.

[0061] The tungsten alloy compact, after being mixed and pressed into shape, is placed in a vacuum hot pressing sintering furnace. When the vacuum is reduced to 5*10, -3 Heating of the compact begins when the pressure drops below Pa, during which the vacuum level is maintained at 1*10. -2 Below Pa. Increase the temperature to 950℃ at a rate of 10℃ / min and hold for 1.5h.

[0062] Step 2: Powder pre-pressurization process.

[0063] When the temperature reaches 950℃ during hot pressing and sintering, the pressing operation begins. A pressure of 15MPa is applied to the pressing, and the pressure should be slowly increased to 15MPa within 5 minutes.

[0064] Step three: solid phase pressure sintering process.

[0065] The pressure was slowly decreased to 5 MPa within 5 min, and then the temperature in the furnace was increased to 1300°C at a rate of 5°C / min, during which the pressure was maintained at 5 MPa. Thereafter, the temperature in the furnace was maintained at 1300°C and kept for 3 h.

[0066] Step four: liquid phase sintering process.

[0067] The pressure was decreased to 0 MPa within 20 min, and then the temperature in the furnace was increased to 1480°C at a rate of 5°C / min and kept for 1 h.

[0068] Step five: cooling process.

[0069] The temperature was decreased to 900°C at a rate of 5°C / min, and then the heating was turned off and the furnace was cooled to room temperature.

[0070] Example 3

[0071] The tungsten alloy compact used in this example was obtained by mixing tungsten powder and nickel-iron powder and then press forming by molding, wherein the tungsten powder accounted for 90% by mass in the tungsten alloy compact. In the nickel-iron powder, the mass ratio of nickel to iron was 7:3, and the density of the tungsten alloy compact was 61.8%.

[0072] A tungsten alloy vacuum hot pressing solid-liquid phase multi-stage sintering method, comprising the following steps:

[0073] Step one: pre-sintering process.

[0074] The tungsten alloy compact after powder mixing and press forming was placed in a vacuum hot pressing sintering furnace, and when the vacuum was reduced to 5*10 -3 Pa or below, the compact began to be heated, and the vacuum degree was maintained at 1*10 -2 Pa or below during the heating. The temperature was increased to 950°C at a rate of 10°C / min, and kept for 1.5 h.

[0075] Step two: powder pre-pressing process.

[0076] When the temperature in the hot pressing sintering reached 950°C, the compact began to be pressed. A pressure of 15 MPa was applied to the compact, and the pressure should be slowly increased to 15 MPa within 5 min.

[0077] Step three: solid phase pressure sintering process.

[0078] The temperature in the furnace was increased to 1200°C at a rate of 8°C / min, and the pressure was maintained at 15 MPa during the process. Thereafter, the temperature in the furnace was maintained at 1200°C and kept for 3 h.

[0079] Step four: liquid phase sintering process.

[0080] The pressure was reduced to 0 MPa within 10 min, and then the temperature in the furnace was increased to 1500℃ at a rate of 8℃ / min, and the temperature was maintained for 0.5 h.

[0081] Step five: cooling process.

[0082] The temperature was decreased to 900℃ at a rate of 10℃ / min, and then the heating was turned off and the furnace was cooled to room temperature.

[0083] Example 4

[0084] The tungsten alloy compact used in this example was obtained by mixing tungsten powder and nickel-iron powder and then cold isostatic pressing. In the tungsten alloy compact, the mass ratio of tungsten powder in the tungsten alloy was 90%. In the nickel-iron powder, the mass ratio of nickel to iron was 7:3, and the density of the tungsten alloy compact was 62.1%.

[0085] A tungsten alloy vacuum hot pressing solid-liquid phase multi-stage sintering method, comprising the following steps:

[0086] Step one: pre-sintering process.

[0087] The tungsten alloy compact after powder mixing and pressing was placed in a vacuum hot pressing sintering furnace. When the vacuum was reduced to 5*10 -3 Pa or below, the compact was heated. During this period, the vacuum degree was maintained at 1*10 -2 Pa or below. The temperature was increased to 900℃ at a rate of 10℃ / min, and the temperature was maintained for 1.5 h.

[0088] Step two: powder pre-pressing process.

[0089] When the temperature in the hot pressing sintering reached 900℃, the compact was subjected to a pressing operation. A pressure of 15 MPa was applied to the compact, and the pressure should be slowly increased to 15 MPa within 5 min.

[0090] Step three: solid phase pressure sintering process.

[0091] The pressure was slowly reduced to 10 MPa within 5 min, and then the temperature in the furnace was increased to 1250℃ at a rate of 5℃ / min, and during this period, the pressure was maintained at 10 MPa. Subsequently, the temperature in the furnace was maintained at 1250℃ and the temperature was maintained for 2.5 h.

[0092] Step four: liquid phase sintering process.

[0093] The pressure was reduced to 0 MPa within 15 min, and then the temperature in the furnace was increased to 1500℃ at a rate of 5℃ / min, and the temperature was maintained for 1 h.

[0094] Step five: cooling process.

[0095] Cooling down to 900℃ at a rate of 5℃ / min, then turning off the heating and cooling down to room temperature with the furnace.

[0096] Example 5

[0097] The tungsten alloy compact used in this example was obtained by mixing tungsten powder and nickel-iron powder and then pressing into shape by die pressing. In the tungsten alloy compact, the tungsten powder accounted for 90% by mass in the tungsten alloy. In the nickel-iron powder, the mass ratio of nickel to iron was 7:3, and the density of the tungsten alloy compact was 62.2%.

[0098] A tungsten alloy vacuum hot pressing solid-liquid phase multistage sintering method, comprising the following steps:

[0099] Step one: pre-sintering process.

[0100] The tungsten alloy compact after powder mixing and pressing into shape is placed in a vacuum hot pressing sintering furnace. When the vacuum is reduced to 5*10 -3 Pa or below, the compact is heated. During this period, the vacuum degree is maintained at 1*10 -2 Pa or below. The temperature is increased to 850℃ at a rate of 5℃ / min, and the temperature is maintained for 1h.

[0101] Step two: powder pre-pressing process.

[0102] When the temperature in the hot pressing sintering reaches 850℃, the compact is subjected to a pressing operation. A pressure of 15MPa is applied to the compact, and the pressure should be slowly increased to 15MPa within 5min.

[0103] Step three: solid phase pressure sintering process.

[0104] The pressure is slowly reduced to 5MPa within 5min, then the temperature in the furnace is increased to 1200℃ at a rate of 5℃ / min, and during this period, the pressure is maintained at 5MPa. Then, the temperature in the furnace is maintained at 1200℃ and the temperature is maintained for 2h.

[0105] Step four: liquid phase sintering process.

[0106] The pressure is reduced to 0MPa within 10min, then the temperature in the furnace is increased to 1450℃ at a rate of 5℃ / min, and the temperature is maintained for 0.5h.

[0107] Step five: cooling process.

[0108] Cooling down to 900℃ at a rate of 5℃ / min, then turning off the heating and cooling down to room temperature with the furnace.

[0109] Comparative Example 1

[0110] The difference from Example 1 is that at 900℃, no pressurization operation is performed. After holding at 900℃ for 1 h, the pressure is directly increased to 10 MPa, and the temperature is increased to 1300℃ at a rate of 5℃ / min and the operation of Step 3 is continued. The rest of the operations are the same as those of Example 1.

[0111] Comparative Example 2

[0112] The difference from Example 1 is that Step 1 and Step 2 are not performed. After heating to 900℃, no holding or pressurization is performed. The pressure is directly increased to 10 MPa, and the temperature is increased to 1300℃ at a rate of 5℃ / min and the operation of Step 3 is continued. The rest of the operations are the same as those of Example 1.

[0113] Comparative Example 3

[0114] The difference from Example 1 is that after 900℃, no pressurization operation is performed. After holding at 900℃ for 1 h, the pressure is decreased to 0 MPa within 20 min. Then the temperature is increased to 1300℃ at a rate of 5℃ / min and held for 3 h. The rest of the operations are the same as those of Example 1.

[0115] Comparative Example 4

[0116] The difference from Example 1 is that no holding operation is performed at 1300℃. After the temperature is increased to 1300℃, the pressure is decreased to 0 MPa within 20 min, and the temperature is increased to 1480℃. The rest of the operations are the same as those of Example 1.

[0117] Comparative Example 5

[0118] The difference from Example 1 is that Step 4 is not performed. After the compact is held at 1300℃ for 3 h, the pressure is directly decreased to 0 MPa within 20 min, and the operation of Step 5 is started. The rest of the operations are the same as those of Example 1.

[0119] Comparative Example 6

[0120] The difference from Comparative Example 5 is that the sample is not subjected to pressurization operation. After the temperature is increased to 1300℃ at a rate of 5℃ / min and held for 3 h, the temperature is directly decreased to 900℃ at a rate of 5℃ / min, and then the heating is turned off and the furnace is cooled to room temperature. This comparative example demonstrates that the method described in the present patent can effectively reduce the solid phase sintering temperature of tungsten alloy.

[0121] The measurement results of the samples of Examples 1-5 and Comparative Examples 1-5 are shown in Table 1.

[0122]

[0123]

[0124] From the results of the samples of Examples 1-5 and Comparative Examples 1-6, it can be seen that the alloy of Example 1 is almost fully dense with fine grain size. Step 1, Step 2 and Step 3 have good effects on the relative density of the alloy, and the relative density of the alloy cannot reach more than 99% without any of the steps. Step 4 has the greatest effect on the relative density of the alloy, and the tungsten alloy without liquid phase sintering is difficult to achieve satisfactory density.

Claims

1. A method for preparing a high-density tungsten alloy, characterized in that: The tungsten alloy billet is heated to the pre-sintering temperature under vacuum, and pressure is applied at the pre-sintering temperature to perform pre-sintering at a pressure of 15-20 MPa. After pre-sintering, the pressure is reduced to 5-15 MPa, and then the temperature is raised to the solid-phase sintering temperature for solid-phase sintering. After solid-phase sintering, the pressure is reduced to 0 MPa, and then the temperature is raised to the liquid-phase sintering temperature for liquid-phase sintering to obtain the tungsten alloy. The pre-sintering temperature is 850-950℃, the solid-phase sintering temperature is 1200-1300℃, and the liquid-phase sintering temperature is 1450-1500℃.

2. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: The tungsten alloy compact is obtained by mixing tungsten powder and nickel-iron-based powder and then pressing them into shape. In the tungsten alloy compact, the mass fraction of tungsten powder is 85-95%. The nickel-iron-based powder contains nickel and iron, and the total mass percentage of nickel and iron is ≥85%; at the same time, the mass ratio of nickel to iron is 6-8:2-4. The pressing method is either molding or cold isostatic pressing.

3. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: The density of the tungsten alloy blank is ≥55%.

4. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: First, place the tungsten alloy billet in a vacuum hot pressing sintering furnace and evacuate it. When the vacuum degree is <5×10 -3 When Pa, begin heating at a rate of 5-15℃ / min to the pre-firing temperature, maintaining a vacuum level <1×10⁻⁶ during the heating process. -2 Pa.

5. A method for preparing a high-density tungsten alloy according to claim 1 or 4, characterized in that: When the pre-firing temperature is reached, the pressure is increased to 15-20 MPa within 5-10 minutes; The preheating time is 1-1.5 hours.

6. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: After preheating, reduce the pressure to 5-15 MPa within 5-10 minutes; The solid-state sintering temperature is increased at a rate of 5-8℃ / min to carry out solid-state sintering; the solid-state sintering time is 2-3 hours.

7. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: After solid-state sintering is completed, the pressure is reduced to 0 MPa within 10-20 minutes.

8. A method for preparing a high-density tungsten alloy according to claim 1 or 7, characterized in that: The temperature is increased to the liquid phase sintering temperature at a rate of 5-8℃ / min, and liquid phase sintering is carried out; the liquid phase sintering time is 0.5-1.5h.

9. The method for preparing a high-density tungsten alloy according to claim 1, characterized in that: After the liquid phase sintering is completed, the temperature is first reduced to 850-950℃ at a rate of 5-10℃ / min, and then cooled to room temperature in the furnace.

10. A high-density tungsten alloy prepared by the preparation method according to any one of claims 1-9.

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