Effects of heat treatment on microstructure and high temperature tensile properties of TiBw/TA15 composite billet with network architecture

In situ 3.5 vol% TiBw whisker reinforced TiBw/TA15 composite with a novel network architecture was successfully fabricated by reaction hot pressing (RHP) method. In order to improve the high temperature mechanical properties of the composite, solid solution and aging treatments with different parameters were carried out. After sintering, the composite formed a net-like microstructure. The strength of composite was improved by the effect of whisker-rich boundary and the interconnected whisker-lean matrix retained its ductility. The elastic modulus and hardness of different phases were tested by nanoindentation for better understanding the strengthening mechanism. The ultimate tensile strength at 600-700 °C of the composite showed the highest value when the solution temperature is 1000 °C followed by aging treatment, which was caused by the distribution of a few residual primary α phases on the boundary and in turn the increasing of volume fraction for the reinforcements. Furthermore, the size and fraction of fine α+β phases increased with increasing of aging temperature after 1000 °C solid solution treatment, leading to the increasing of ductility and decreasing of strength for the composite tested at 600-700 °C. The above results showed that the composite with novel network architecture could be strengthened by heat treatments at high temperature environment, e.g. the ultimate tensile strength could be improved more than 200 MPa at 600 °C, and more than 100 MPa at 700 °C.