Study On Microstructure And Properties Of TiBw Reinforced Titanium Matrix Composites

The aim of this paper is to study the microstructure and properties of TiBwreinforced titanium matrxi composites. Based on the design of quasi-continuousnetwork structure，a range of titanium matrix composites which were reinforced bylow levels of TiBw（≤3.0vol.%） were successfully fabricated by in situ technique，low energy ball milling and hot-pressing sintering processes. Large and spherical Tipowders and fine TiB₂powders were employed as raw material.The effects of heattreatment on microstructure and mechanical properties of TiBw/TC4compositeswere studied.Microstructure of the as-sintered and as-heattreated composites was observedby OM and SEM. The volume fractions of reinforcemet were different. Themorphology and distribution of matrix and reinforcement were studied. Roomtemperature and high temperature mechanical properties of different compositeswere measured. The morphology of fracture surfaces was also studied by SEM. Bystudying the plastic deformation behavior and observing the morphology of fracture,the strengthening mechanism was analyzed.Depending on the microstructures of TiBw/Ti composites, the reinforcementwith the shape of rod and whisker was distributed homogeneously around the Tiparticles. The grain size as well as lath size is obviously refined by small contentof TiB（≤0.25vol.%）. The composites were strengthened significantly. The resultsshowed that，the strength of material increased significantly and then the speed ofincrease reduced with the reinforement increasing. The as-sintered0.25vol.%TiBw/TC4composites exhibited much higher strength975MPa and ductility22.84%than those of the TC4alloy. The ductility of present composites was higherobviously than the composites which was fabricated by traditional powdermetallurgy method. The fracture mechanism was typical ductile fracture because ofthe obvious dimples and teerring edges.Effects of quenching and aging temperatures on TiBw/TC4compositesstructure and properties were analysed. The results of tensile testing showd that，with the increas of quenching temperatures, the ultimate tensile strength rised butthe elongation decreased. While the result was opposite with the increas of agingtemperatures. After quenching at930℃and aging for4hours at550℃, thestrength of composites were effectively enhanced，especially high temperatureproperties. Using this technology, the tensile strength of0.25vol.%TiBw/TC4composites reached652MPa at550℃，improved largely than the that of the as-sintered composites which was450MPa.