Research On Hot Extrusion And Heat Treatment Of TIBW/TI6AL4V Composites

TiBw/Ti6Al4V composites with a uniform network microstructure were fabricated by in situ reactive hot processing by the system of Ti6Al4V and TiB2 powers.The average size of the original Ti6Al4V and TiBw powders were 110μm and 5μm respectively. The effects of hot extrusion and heat-treatment on microstructure and properties of composites were studied. The microstructures of the composites were studied with SEM and optical microscope. The tensile properties of composites at both room and high temperatures were measured.Microstructure analysis results showed that TiB is rodlike whisker,which distributed around the boundaries of Ti6Al4V matrix particles as-received. The TiB whisker subsequently formed into network structure.After extrusion microstructure analysis results showed that the network structure were damaged.TiB whiskers were broken and rotated distributing along the extrusion direction and local volume fraction of TiB whiskers were decreased. It can be seen in longitudinal section the distribution of TiB whiskers in extruded composites with the extrusion ratio 16:1 were more discrete than the extrusion ratio 9:1,which guaranteed connectivity of matrix alloy. The effects of heat treatment solution temperature and aging temperature on microstructure and mechanical properties of extruded composites were investigated.The results show that with increase of solution temperature primary volume fraction decreases. With the aging temperature increased,the martensite decomposition product size increases,at the same time strip phase grows integration.The room temperature tensile strength of 5vol.%TiBw/Ti6Al4V sintered composites was 1030MPa and the elongation of composites was 3.2%.As 8vol.% TiBw/Ti6Al4V sintered composites,tensile strength was 1232MPa and the elongation was 1.3%. After the composites extruded at 1100℃,compared to sintered composites,the tensile strength and especially their elongationt were greatly improved. Tensile strength of 5vol.% and 8vol.% extruded composites were 1206MPa and 1311MPa,compared with sintered 17.1% and 6.5%.The elongation were 12% and 4.8% respectively,compared with sintered composites were increased by 275% and 269%. The strength and ductility of extruded composites were improved with the increase of extrusion ratio. 5vol.% of composite quenched at 990℃aging at 600℃have better mechanical properties,its tensile strength is 1364MPa,elongation 7.8%. The 8vol.% of composite with the same heat treatment tensile strength was 1469MPa,elongation was 2.5%.The high temperature tensile results show that with the the increase of testing temperature strengthening effect is weakened.At 400℃,tensile strength of 5vol.% and 8vol.% composites after heat treatment were 1042Mpa and 1158MPa.At 700℃,5% and 8vol.% composites have considerable strength,which were 215Mpa and 223Mpa respectively.