Study On Preparation,Microstructure And Properties Of Multicomponent Tungsten Alloy

High density tungsten alloy has excellent physical and mechanical properties such as high density,high tensile strength,good electrical and thermal conductivity,good ductility,low tritium inventory,etc.It is widely used in gyroscope rotors,bullets,electrical contact materials,die-casting moulds,plasma facing materials,etc.With the rapid development of military,aerospace,electronics and nuclear industries,research on the design of multiple components of tungsten alloys,optimization of preparation processes,addition of trace elements,grain refinement and performance toughening has developed rapidly.To study the effects of doping rare earth oxides,binder type and sintering process on the microstructure evolution and mechanical properties of tungsten alloys,this paper investigates trace CeO₂ doping of W-5Ni-3Cu ternary alloys,optimization of two-step sintering process of 90W-6Ni-4Co ternary alloys,two-step sintering of W-Ni₃Al alloys with Ni₃Al binder,preparation of 90W-6Ni₃Al-4Co ternary alloys with Ni₃Al instead of Ni and W-Ni₃Al-Co ternary alloys with different Ni₃Al/Co ratios.The influencing mechanism of microstructure on properties is revealed,and the relationship between component,technology,microstructure and properties is also established by revealing the mechanism of CeO₂,Ni₃Al and two-step sintering on the microstructure evolution of tungsten alloy such as grain growth,phase distribution and densification.The W-5Ni-3Cu system alloys are prepared by a two-step sintering technique with CeO₂powder as an additive.A comparative study shows that the relative density of W-5Ni-3Cu alloys with CeO₂ addition are lower than that of the alloy without CeO₂;the shape of W phase changes from irregular polymorphic to elliptical,and its average grain size decreases first and then increases.The grain size of W-5Ni-3Cu-0.4CeO₂ alloy is the finest,and has an interfacial strengthening effect,which makes the comprehensive performance of W-5Ni-3Cu-0.4CeO₂ is the best;the main fracture type is W/bonded phase interfacial fracture in W-5Ni-3Cu model alloy.Based on the two-step sintering technology,90W-6Ni-4Co mixed powder is ball milling,and the alloy is prepared by solid phase sintering and two-step sintering processes.The particle size of milled powders increases firstly due to sheet and agglomeration of particles and decreases later for fracture of particles during a mechanical alloying process.The shapes of W-rich particles change from stripes to network,to polygonal and to subsphaeroidal finally.The mechanical properties can be attributed to the synergistic e ect of densification,grain refining and distribution of the W-rich phase and binder phase.The samples are characterized by excellent comprehensive property during two-step sintering with short dwelling time of 5 min.In order to further explore the effect of Ni₃Al on the microstructure and properties of W-Ni₃Al alloys,W-Ni₃Al alloys with different Ni₃Al contents are prepared by high-energy ball milling and two-step sintering technology.It is found that Ni₃Al reacts with oxygen in the air to form?-Al₂O₃ phase during ball milling and drying,and its content increases with the increase of Ni₃Al content,which effectively inhibits the growth of W phase and refined the structure;?-Al₂O₃ phase refinement,interfacial strengthening and densification effects can significantly promote the mechanical properties of the W-Ni₃Al alloy.However,the mechanical properties of W-Ni₃Al alloys are much lower than that of 90W-6Ni-4Co alloys due to the inhomogeneity of?-Al₂O₃ phase arrangement.For the degradation of mechanical properties of W-Ni₃Al alloy,90W-6Ni₃Al-4Co alloy is prepared by two-step sintering by partially replacing Ni as binder by Ni₃Al.The(Ni,Co)₃Al₄and Co₂Al₉ phases are formed.The reaction temperature of phases would be reduced by using Ni₃Al.The average grain size increase,and microstructure is compact with increase of sintering temperature.The fracture modes by bending test mainly include binder phase rupture,W–W grain boundary separation,and W-binder phase interface separation.The fracture modes by compressive test include toughness and brittleness.In order to further control the organization and properties of Ni₃Al bonded-phase tungsten-based alloys,W-Ni₃Al-Co alloys with different Ni₃Al/Co ratios are prepared by a two-step sintering.The results show that rich-W phase is arranged at network structure and refining with Ni₃Al/Co ratios increase.The compressive deformation behavior of W-7Ni₃Al-3Co alloy with excellent compressive properties is investigated by EBSD technique.The results demonstrate the twin in the binder phase can hinder stress concentration in binder phase and the interface of W/binder phases through the twin-dislocation interaction.The W network structure is uniform global deformation which restricts grain boundary sliding during deformation and prevents the crack extension and consolidation.The twin in binder phase and W network structure are both important factors for improving compressive properties of W-Ni₃Al-Co alloys.