Preparation And Investigation On Microstructure And Properties Of Ultra-fine Grained Tungsten Alloys

Tungsten alloy is one of the most important refractory materials,which plays an important role in national defense,aerospace and other fields.Refining alloy structure is an effective means to improve the properties,which is also the main trend of current research and future development.In this paper,W-Ti,W-Cr,W-Ni,W-Ti-Cr and W-Ti-Ni alloys were prepared by cold-pressing sintering and spark plasma sintering.The microstructure and properties of the samples were studied.The thermodynamic action and refinement mechanism of alloying elements were also analyzed.The results showed that:(1)Tungsten alloy samples with submicron W grain size could be prepared by both cold-pressing sintering and spark plasma sintering.The densities of the samples reached more than90%.Samples nearly full densification could be prepared by spark plasma sintering.(2)High energy ball milling could make Ti,Cr and Ni form supersaturated solid solution in W.The average grain size of W in the W-Ti,W-Cr and W-Ti-Cr alloys prepared by subsequent cold-pressing sintering were all in the submicron scale.W-Ti alloy contained Ti_xW_1-x phase,which could be divided into W-rich phase(?₂)and Ti-rich phase(?₁).W-Cr alloy contained W-rich phase(W_ss)and Cr-rich phase(Cr_ss).With the increase of Ti and Cr content,the grain size first decreased and then increased.There were three optimal components:W80Ti20,W75Cr25 and W-20Ti-20Cr(at%),which average grain sizes of tungsten were 590nm,520 nm and 450 nm,the densities were 94.5%,91.6%,92.3%,the hardness were 763 HV,572 HV and 753 HV,the compressive strength were 746 MPa,545 MPa and 682 MPa,the fracture strain were 2.6%,2.3%and 2.4%respectively.With the increase of Ti and Cr contents,the strength first increased and then decreased,which was consistent with the grain refining behavior.According to the analysis,both of the W-Ti and W-Cr alloy systems were strongly segregation systems.The segregation behavior of Ti and Cr elements at the W grain boundary could significantly reduce the interface energy so as to inhibit the grain growth.By adding Ni to the W-Ti system,W-20Ti-10Ni and W-20Ti-15Ni(at%)alloys were prepared,which were composed of Ti_xW_1-x phase and?phase.The average grain size of tungsten increased to 720nm and 780 nm,the fracture strain increased to about 6%,the densities were 94.1%and 93.7%,the hardness were 632 HV and 608 HV,the compressive strength were 621 MPa and 609 MPa respectively.Plasticity is markedly improved.(3)W-Ni,W-Ti and W-Ti-Ni alloys were prepared by spark plasma sintering.Compared with the cold-pressing samples,the density,strength and plasticity of the samples were all greatly increased,meanwhile,the ultrafine microstructure was still maintained.Among them,the average grain size of W of W85Ni15 was 1.08?m,the density was 95.2%,the hardness and compressive strength was 546 HV and 1932 MPa respectively,the fracture strain was 47.5%.The grain size of W-Ti alloys decreased first and then increased with the increase of Ti content,and the strength increased first and then decreasesd,which was consistent with the grain refinement behavior.The W75Ti25(at%)alloy was nearly full dense,with the density of 98.5%.The average grain size of W was 340 nm,the hardness and compressive strength was 860 HV and 2598 MPa respectively,the fracture strain was 10.4%.The Ni element was added into the W-Ti alloy to prepare W-25Ti-10Ni(at%)alloy.The average grain size of W was 520 nm,the density was 98.1%,the hardness and compressive strength was 763 HV and 2293 MPa respectively,the fracture strain was 19.2%.This alloy system had good comprehensive performance and maintaining ultrafine structure.