Study On Microstructures And Properties Of TC4/TiAl Gradient Materials By Laser Engineered Net Shaping

TC4 is the most widely used titanium alloy at present with the excellent comprehensive performance,which can work stably below 500?,and is widely used to manufacture compressor disks,bulkheads,and landing gears.TiAl alloy can work stably below 900?and is widely used in the aerospace field,with its characteristics of high melting point,low density,high elastic modulus,excellent high-temperature strength,good oxidation resistance,and flame retardant performance,such as engine nozzles,exhaust valves,and transition duct beams and other structural parts.Connecting TC4 alloy and TiAl alloy to manufacture TC4/TiAl gradient materials can give full play to their respective characteristics,and propose new design ideas for reducing weight and improving the performance of structural parts in the aerospace field.In this paper,TC4 and TiAl were connected to manufacture TC4/TiAl gradient materials through the gradient transition by Laser Engineered Net Shaping?LENS?technology to meet properties under different working conditions.The transition of the TC4/TiAl gradient material designed in this study is100%TC4-80%TC4+20%TiAl-60%TC4+40%TiAl-40%TC4+60%TiAl-20%TC4+80%TiAl-100%TiAl.The TC4/TiAl gradient materials sample and TC4+TiAl mixed powder alloy samples without metallurgical defects were successfully prepared using the best process parameters obtained by a large number of previous experiments.The evolution of the microstructure,composition distribution,phase composition and fracture morphology of four TC4+TiAl powder mixture alloys?80%TC4+20%TiAl,60%TC4+40%TiAl,40%TC4+60%TiAl and 20%TC4+80%TiAl?and five transition interfaces of TC4/TiAl gradient materials?TC4/80%TC4+20%TiAl?80%TC4+20%TiAl/60%TC4+40%TiAl?60%TC4+40%TiAl/40%TC4+60%TiAl?40%TC4+60%TiAl/20%TC4+80%TiAl and20%TC4+80%TiAl/100%TiAl?were analyzed by OM,SEM,EDS,XRD,EBSD,and TEM.The room temperature and high-temperature tensile properties of TC4/TiAl gradient material and TC4+TiAl mixed powder alloy were tested by the universal testing machine.The test results show that with the increase of TiAl contents?0%,20%,40%,60%,80%,and 100%?in the TC4/TiAl gradient materials,the microstructure transformed from basket weave structure to lamellar structure,the contents of Al,Nb,and Cr elements gradually increased,and the contents of Ti and V elements gradually decreased.From the TC4 side to the TiAl side,the phase composition evolutions were?+?????+?₂+?/B2??₂+?/B2??₂??₂+?+?/B2???₂+??+B2.The structures near the five transition interfaces were dense and all formed good metallurgical bondings.The TC4/TiAl gradient materials showed a quasi-cleavage fracture with the ultimate tensile strength of 308 MPa and the elongation of1.8%.The addition of TiAl?20%,40%,60%and 80%?can reduce the strength and plasticity properties of TC4+TiAl powder mixture alloys at room temperature,the 80%TC4+20%TiAl alloy has the highest ultimate tensile strength and elongation,which were 1083 MPa and4.60%,respectively.The 40%TC4+60%TiAl mixed powder alloy exhibited the best tensile strength at 650?and 750?,which was 572 MPa and 562 MPa,respectively.