| Recently, high temperature titanium matrix composites (TMCs) were widely used in aerospace, marine and power generation due to their higher specific strength, specific modulus, superior creep, fatigue and wear resistance. Therefore, it was necessary and important to improve the mechanical properties at elevated temperature. In situ composites offered the advantage of homogeneous dispersed borides with contaminant-free boride matrix interfaces. They were easier to fabricate and thus reduce the cost.βheat treatment was performed for laminar microstructures after rolling because lamellar microstructures exhibited higher temperature creep properties, impact toughness and fracture toughness. It has been demonstrated that low concentrations of boron addition in titanium alloys led to increased stiffness, enhanced elevated temperature strength, good creep performance, fatigue resistance and wear resistance. Rare earth element was able to decrease the oxygen content through reaction with oxygen and form rare earth oxide which was hard and thermal stable ceramic particles. Furthermore, Rear earth element could refine the grain size of the matrix alloy and increase their oxidation resistance. The mechanical properties of TMCs at elevated temperature depended on the microstructures and interfaces of reinforcements and matrix. However, it was necessary to obtain the optimal content of reinforcements to optimize mechanical properties.In the present work, TMCs reinforced with different volume fraction of TiB plus La2O3 were in situ synthesized by common casting and hot-forging technologies. Microstructure of composites and reinforcements were investigated by X-Ray Diffraction (XRD), Optical Microscopy (OM), and Scanning Electronic Microscope (SEM) to understand the strengthening effect of reinforcements. The heat treatment temperatures of the TMCs were 10℃and 20℃above theβtransus points for fully laminar microstructure. It was expected to be a theoretical basis to design and optimize the microstructure structures and the properties of TMCs through the investigation of microstructure and mechanism. In this research, the main work was done as following:(1) Reinforcements TiB whiskers and near-equiaxial La2O3 were distributed uniformly in the titanium matrix. The black needle shapes TiB whiskers were primarily aligned along the rolling direction and uniformly dispersed among the matrix. Interfaces between reinforcements of TiB and Ti matrix were clean without any interfacial reactions.(2) Tensile tests at room temperature were very sensitive to the matrix of composites. Research indicated that composites heat-treated at Tβ+10℃obtained fine grained microstructures and superior mechanical properties. Poor heat treatment Tβ+20℃led coarse microstructures and the ductility reduced about 70% compared composites heat-treated at Tβ+10℃. Thensile test at high temperature indicated that coarse microstructure in composites (Tβ+20℃) weakened the strengthening effect of reinforcements on matrix. Composites differed in reinforcements displayed similar strengths at every temperature.(3) The relationships between volume fraction of reinforcements and mechanical properties were investigated. Aspect ratio of TiB whiskers played the critical role in strengthening effect. At room temperature and 600?C, the TiB whiskers beared loading effectively, but at 650?C and 700?C, debondings between Ti and TiB whiskers were responsible for the failure. TMC2 with medium volume fraction of reinforcements gave the highest aspect ration of TiB whiskers amd best mechanical properties at tensile tests and creep tests. The effective strengthening of TiB whiskers and fine microstructures played the dominant role in TMC2.
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