Effects of volume fraction of reinforcement on tensile and creep properties of in-situ TiB/Ti MMC

摘要

High temperature applications of titanium matrix composite (TMC) are expected to have appreciable improvements in elastic modulus, strength and physical properties than monolithic alloys[l-5]. It has been reported that the different interfacial reactions resulting from various processes or reinforcements significantly affect the mechanical and physical properties of TMC[6-91. Moreover, the breaking down of reinforcements imposed by the following thermomechanical process (TMP) also depends on the interfacial condition[10, 11]. Recently, the creep behaviors of TMC are highly concerned for applica-tions of aerospace structure, propulsion system, and power generation system. However, the creep mechanisms of TMC and relevant factors associated with activation energy, stress exponent and threshold stress are not clear in detail. For aluminum and some other alloy matrix composites, although the concept of threshold stress and stress exponent have been widely introduced to correlate the strengthening mechanism of creep, the origin of threshold stress is still not well understood. In a study of TMC reported by Ranganath et a1.[12], the values of stress exponent were measured to be excep- tionally high (6-7) due to the transition of creep mechanism from lattice to pipe diffusion at 823 K, and a kinetic strengthening term involving volume fraction of reinforcement to the constitution equa-tion of power-law creep was proposed to interpret the results that creep data cannot merge even aftercompensating for threshold stress.