LIU Yulong, LEI Xinhua, LI Yun, PAN Wenqiang, QIU Dekun, XIA Junjie, ZOU Jianpeng
【Objective】 Tungsten copper alloy has high density, high kinetic energy, high sound velocity, high ductility，high strength and low expansion coefficient, so it is widely used for petroleum perforation drug cover materials, anti-armor weapons, etc. Compaction pressure plays a decisive role in the green compact density, which in turn affects the sintered compact density and relative density, and ultimately the penetration performance of tungsten-copper drug cover materials. Therefore, the traditional powder metallurgy compaction and sintering method was adopted to prepare W80Cu20 composites in this paper. The effects of compaction pressure on green compact density and strength as well as the effects on sintered compact density and microstructure were studied. The compaction process of WCu alloy based on Huang Peiyun's double logarithmic compaction equation was investigated.
【Method】 W powder (99.9wt%) and Cu powder (99.9wt%) that have not been specially treated were selected as raw materials to prepare W80Cu20 composite materials. The preparation process is as follows: 400 g of W powder and 100 g of Cu powder were weighed according to the mass ratio. Stearic acid was ground through a 325-mesh sieve and added to the WCu mixed powder with mass fraction of 0.5%. The mixture was then mixed in a V-type mixer for 4 h at a speed of 60 r/min to obtain the W80Cu20 mixture. The mixture was loaded into a ϕ10 mm mold and pressed under pressures of 100, 200, 300, 400, 500, 600, 700, and 800 MPa in sequence. Finally, the W80Cu20 green compacts were sintered in an argon-protected atmosphere. The sintering process involved heating to 370 ℃ for 1 h, maintaining the temperature for 1 h, then heating to 1 000 ℃ for 3 h, maintaining the temperature for 1 h, and finally natural cooling.
【Result】 The significant increase in density and compressive strength of W80Cu20 green compacts during the early and middle stages of compaction is primarily due to the rapid rearrangement of particles and elastic-plastic deformation within the compacts as the compaction pressure increases. Small particles quickly fill the voids between larger particles through sliding and rotation, leading to local and overall deformation of the W80Cu20 powder, thereby rapidly enhancing the density and compressive strength. The increase in compressive strength of the compacts slows down during the later stages of compaction, mainly because severe work hardening has already occurred, making it more difficult to further increase the density and compressive strength. The composite exhibits the highest compressive strength at 700 MPa, reaching 106.76 MPa. Therefore, 700 MPa is the optimal pressing pressure for W80Cu20 green compacts. The density of the sintered compacts follows the same trend as that of the green compacts. Under compaction pressures ranging from 100 to 600 MPa, the relative density of the sintered compacts increases significantly, however, the increase slows down between 600 and 800 MPa. At lower compaction pressures, there are many pores between W grains and Cu grains in the sintered compacts, with uniform distribution of W and Cu phase structures and no segregation phenomena. As the compaction pressure increases, the pores in the sintered compacts decrease, the W grains become more tightly bound, and the Cu phase structure is uniformly distributed between the tungsten grains, leading to an increase in the density of the sintered compacts.
【Conclusion】 (1) After being mixed for 4 h using a V-type mixer, the W80Cu20 powder exhibits uniform distribution with no obvious agglomeration or segregation. The optimal pressing pressure for the W80Cu20 green compact is 700 MPa, and its green compact density, relative density, and compressive strength are 13.53 g/cm3, 86.5%, and 106.76 MPa, respectively. (2) The microstructure of W80Cu20 green compacts and sintered compacts is uniform. As the pressing pressure increases, the density, relative density, and compressive strength of W80Cu20 green compacts gradually increase, with a significant increase when the pressing pressure ranges from 100 to 600 MPa.The increase slows down when the pressing pressure ranges from 600 to 800 MPa. The density and relative density of W80Cu20 sintered compacts also increase with the increase of pressing pressure. (3) The relationship between the pressing pressure and green compact density of W80Cu20 composite material conforms to Huang Peiyun's double logarithmic compaction equation. The correlation coefficient of the experimental data fitting curve is 0.990 4. Both the m value (3.11) and M value (128.04) of the WCu mixed powder are at a relatively low level, indicating the good compaction performance of W80Cu20 composite.
