Study On The Microstructure And Mechanical Properties Of AlCoCrFeNi/Ti-47Al-2Cr-2Nb Composites By Powder Metallurgy

γ-Ti Al is considered as an ideal high temperature and light weight structural material,which shows a wide application prospect in aerospace field.However,the engineering applications of many gamma-tial alloys are limited by their low tensile plasticity at room temperature and low deformation capacity at high temperature.A new type of high entropy alloy with excellent high temperature performance was selected as the reinforcing material.By powder metallurgy,the high entropy alloy particles were introduced into theγ-Ti Al alloy to prepare the high entropy alloy evenly distributedγ-Ti Al matrix composite.The main conclusions of this study are as follows:（1）Ti-47Al-2Cr-2Nb prealloy powder and AlCoCrFeNi high entropy alloy powder were sintered at 1200°C,30 MPa and 1 h by vacuum hot pressing and hot extrusion.A new type of gamma-tial matrix composite based on Ti-47Al-2Cr-2Nb alloy was successfully prepared.AlCoCrFeNi was uniformly distributed in the matrix in the form of spheroids,strips and dots.（2）The elements Ti,Al and Nb are completely diffused uniformly in HEA particles,while the diffused layers of Fe,Co,Ni and Cr are not completely diffused with the matrixγ-Ti Al phase andα₂-Ti₃Al phase about 10μm.Due to the diffusion of elements,the AlCoCrFeNi high entropy alloy region changes from BCC and FCC to BCC and B2phases.The addition of AlCoCrFeNi also changes the crystal plane spacing of the matrix structure,resulting in lattice distortion effect.Good interface,grain refinement and lattice distortion effect are the guarantee of high strength plastic composites.（3）The tensile strength ofγ-Ti Al matrix composites decreases with increasing temperature and decreasing strain rate.At the same temperature,with the increase of AlCoCrFeNi content from 0 to 6 wt.%,the tensile strength of the composites gradually increases,but the elongation increases first and then decreases.When the content of AlCoCrFeNi is 4 wt.%,the composite has the best mechanical properties（4）The fracture mode ofγ-Ti Al matrix composites is intergranular at 800°C,intergranular with ductile at 900°C,and ductile at 1000°C.At the beginning of high temperature tensile,AlCoCrFeNi first begins plastic deformation and produces a large number of dislocations.At this time,Alcocrfeni will be constrained by the undeformed Ti-47Al-2Cr-2Nb,and the deformation of the two metals is inconsistent,resulting in back stress.The strength and plasticity ofγ-Ti Al matrix composites are enhanced by back stress strengthening.（5）Power dissipation diagram and thermal working diagram of Ti-47Al-2Cr-2Nb andγ-Ti Al matrix composites with 4 wt.%and AlCoCrFeNi content constructed based on dynamic material model at 0.2～0.8 strain.The optimal range of hot working parameters is 975°C～1000°C,1×10^-1 s^-1,1×10^-3 s^-1 and 955°C～1000°C,1×10^-1 s^-1,1×10^-3 s^-1.The addition of AlCoCrFeNi increases the power dissipation of Ti-47Al-2Cr-2Nb and increases the range of thermal working parameters.