Microstructure And Properties Of SiCnw Reinforced Titanium Matrix Composites

As one of the nearly-α high-temperature titanium alloys,Ti60,due to its light weight,high strength,good thermal strength and thermal stability,has attracted much attention in the aerospace field.However,the application of Ti60 has been limited because of its poor ductility al low temperatures and poor performance at high ternperatures.However,the properties of Ti60 alloy can be improved by introducing reinforcement.In this work,Ti60 alloy powder is used as matrix and SiCnw as reinforcement.By spark plasma sintering,the ball milling mixed SiCnw/Ti60 powder turns into SiCnw/Ti60 composites.The effects of sintering temperature,amount of SiCnw and hot rolling on the microstructure and mechanical properties of the composites were systematically studied.After mixing Ti60 alloy with SiCnw powder at 300 r/min for 4-6 h,SiCnw was uniformly embedded into the Ti60 powder ball,and the phase structure of SiCnw/Ti60 powder did not change significantly.Then,plasma activation sintering was carried out at different sintering temperatures.With the increase of sintering temperature,the pores in SiCnw/Ti60 composite gradually disappeared,and the density increased significantly.The microstructure changed from a large number of equiaxed grains to a bimorphic structure in which equiaxed grains coexist with β grains.The density and mechanical properties of the composites sintered at 1000℃ are the best.The SiCnw/Ti60 composites with different content of SiCow were sintered at the optimum temperature of 1000℃.With the increase of SiCnw,the large-sized β grains refined,the number of α phases increased,and the grain size of SiCnw/Ti60 composite decreased obviously.Compared with Ti60 alloy,the grain size of sintered composites decreases by 81.9%when the content of Si,Cnw is 0.5 wt.%.At the same time,the hardness of the material is obviously improved,the fracture toughness is reduced,and the tensile property increases first and then decreases with the content of SiCnw.The tensile fracture of sintered Ti60 alloy and composites is composed of a large number of tearing which is due to the low plasticity of Ti60 alloy matrix.After hot rolling at 900℃/20 min for sintered composites with different content of SiCnw,the β-grains elongated and fractured along the rolling direction,and the number of intergranularα phases increased.Compared with the sintered state,the hardness of the hot-rolled composites is obviously improved,and the fracture toughness is further improved.After hot rolling,the ultimate tensile strength of the composites containing 0.5 wt.%SiCnw reaches 1454 MPa,which is 17%higher than that of the original alloy.In the hot rolled tensile fracture,there are a lot of dimples and fractured SiCnw.The high temperature mechanical properties test shows that the tensile strength of the composites increases with the increase of SiCnw content at 500℃and 600℃,and the ultimate tensile strength of the composites with 0.5 wt.%SiCnw content reaches 728 MPa at 600℃.When stretched at 700℃,the tensile strength does not increase with the increase of SiCnw content,or even decreases.This is caused by the oxidation of the matrix during the softening and stretching process at 700℃.