High Temperature Endurance Properties Of In Situ Synthesized Titanium Matrix Composites

Titanium matrix composites (TMCs) are considered as one of the most competitive high temperature structural materials in the field of aviation and aerospace owning to their high strength and elastic module compared to their weight, especially their good mechanical properties at elevated temperature. Particles reinforced TMCs synthesized by in situ are attracted more and more attention because the reinforcements are distributed uniformly and the matrix-reinforcements interfaces are clean, well bonded, and thermodynamically stable which make the properties of TMCs stable at elevated temperature. Moreover, they are cost-efficient and easy fabricated. As high temperature structural materials, TMCs synthesized in situ lie on their high temperature endurance properties deeply for their practical application. However, researches are rarely in this aspect. Therefore, it is important to investigate the endurance properties of in situ synthesized TMCs at elevated temperature.In this work, the high temperature endurance properties of two novel in situ synthesized TMCs (TiB+La₂O₃)/Ti and (TiB+TiC+La₂O₃)/Ti were investigated. It not only provides an experimental reference to the practical application of these two TMCs, but also provides a theoretical and experimental basis for the further research of the high temperature endurance properties and a further improvement of service temperature for in situ synthesized TMCs.In this work, the composites were in situ synthesized by a consumable vacuum arc remelting furnace based on the reaction between Ti, C4B, LaB6 and oxygen in raw materials. The high temperature endurance properties were tested and analyzed. The microstructure of composites and reinforcements were investigated by X-Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electronic Microscope (SEM) and Transmission Electronic Microscope (TEM) to discuss the relationship between the reinforcements and the high temperature endurance properties of composites. In this research, the main work was done as following:1. For contrast study, the matrix alloy was synthesized by the same way. The matrix and composites were heat-treated with a same condition to unify the microstructures of matrix. After heat-treatment, the matrix and composites showed the same near-basket-shape microstructure.The reinforcements were distributed homogeneously and the matrix-reinforcements interfaces are clean and well bonded. TiC showed a near-equiaxial shape and TiB showed a needle shape. TiB reinforcements in (TiB+La₂O₃)/Ti were more gracile than those in (TiB+TiC+La₂O₃)/Ti. Nano-sized La₂O₃ particles distributed uniformly in both of the composites. They had a same average diameter in two composites.2. The high temperature endurance properties were tested and found that the high temperature endurance properties of the composites were improved a lot compared with the matrix alloy owning to the reinforcements enhanced the deformation resistance of composites. (TiB+La₂O₃)/Ti composite has the best high temperature endurance properties. (TiB+La₂O₃)/Ti has one exponential improvement compared with the matrix alloy in steady-state rate and creep rupture life.3. The creep rupture surfaces and the reinforcements were investigated and found that TiB and TiC reinforcements in (TiB+TiC+La₂O₃)/Ti mainly disabled through debonding with the matrix, while TiB reinforcements in (TiB+La₂O₃)/Ti disabled by cracking which were more efficient in undertaking load and improving the high temperature endurance properties than TiB and TiC reinforcements in (TiB+TiC+La₂O₃)/Ti composite.4. The percentage elongations after creep rupture were measured and showed that the percentage elongations of the composites did not decrease, because the plasticity of the matrix alloy in composites were improved by the forming of La₂O₃ through capturing oxygen in the matrix which is bad for the plasticity.