Microstructure And Mechanical Properties Of TiBw/Ti65 Composites

Ti65 particles with an average particle size of 150?m and Ti B2 powder(3?m)were used as raw materials.Low-energy ball milling and hot-press sintering were used to prepare Ti Bw/Ti65 composite material with different reinforcing phase contents based on in-situ autogenous reaction and powder metallurgy techniques.Si element was also added to further improve the using temperature.By adjusting the reinforcing material content,solution and aging temperature and rolling deformation of the composite material,the room temperature tensile and high temperature tensile properties of the test material were tested,and the fracture and toughening mechanism of the composite material were analyzed.The resulting composites were characterized by optical microscopy(OM)and scanning electron microscopy(SEM).Microstructure analysis shows that the macrostructure of the titanium matrix composites of good morphology,and there are no obvious defects such as pores and interface reactions,The size of the preformed powder has little effect on the microstructure of the composites.The addition of Ti Bw can improve the structure of the matrix alloy.Ti Bw are distributed around the matrix alloy in the form of a network structure.This kind of network structure plays a role similar to grain boundary and can effectively improve the strength of the composites.The matrix is nearly equiaxed(?+?)two-phase structure,? phase is distributed in ? phase,and the two phases are closely combined.With the increase of Ti Bw content,the matrix and network structure of the composites did not change significantly,only the distribution density of the reinforced phase increased.The addition of a small amount of Si also had no obvious effect on the morphology of the composites.The heat treatment system of solution aging can effectively improve the matrix structure of the composites,and the heat treatment has little effect to the reinforcement phase.When the solution temperature rises to more than 1100?,the primary ? phase of the composites disappears completely after the heat treatment,and the existence of precipitated phase also decreases obviously.The analysis of mechanical properties shows that the tensile strength and plasticity of 1wt.% Ti Bw / Ti65 composites at room temperature were significantly higher than that of Ti65 matrix alloy,which were 1086 MPa and 5.0%,compared with Ti65 alloy,it was increased by 15.2% and 51.5% respectively.The high temperature strength of the sintered composites was significantly higher than that of Ti65 matrix alloy,from511 MPa to 602 MPa.Ti Bw strengthened the grain boundary,while Si increased the oxidation resistance of the composites,which improved the high temperature strength of the composites.The heat treatment system of solution aging had a more obvious effect on the high temperature properties of the material.The tensile strength of 2wt.% Ti Bw /(Ti65-0.5Si)after solution treatment at 1100 ? and aging treatment at 700 ? was698 MPa,which was 36.6% higher than that of the matrix alloy.After hot rolling deformation,the network structure in ND direction was compressed and enlarged,the network structure in TD direction was compressed and elongated,the network structure in RD direction is compressed,the grains were refined and obviously elongated,and a large number of dislocations were generated in the composites.With the increase of rolling deformation,the microstructure of matrix changed from fine lamellae to equiaxed structure,and recrystallization equiaxed structure appeared around the network structure.After deformation,the whisker broke seriously,and the connectivity degree decreased.When the rolling deformation is 40%,the tensile strength at room temperature reached 1414 MPa,and the elongation was13.8%.The tensile strength at 700 ? was 18.5% higher than that of the sintered composites.In the process of rolling deformation,the whisker broke seriously and the whisker was arranged non-directionally,the connectivity of the reinforcement decreased,and the whiskers perpendicular to the rolling direction were obviously flattened,so the distribution of the reinforcement phase became more uniform and dispersive than the regular distribution of the sintered network structure on the longitudinal tensile fracture along the RD direction.