Modification of microstructure and tensile property of TiBw/near-α Ti composites by tailoring TiBw distribution and heat treatment

The 5.1 vol% TiB whisker reinforced Ti60 (near-α Ti alloy) composites were successfully fabricated by reaction hot pressing technology. In order to modify their microstructure and property, the effects of precipitates on the designed network structured composites were investigated by heat treatment without any deformation. The microstructure results show that the ordered α2 phase with the size of 5 nm-10 nm is precipitated from matrix due to high content of α stabilizing elements and the slow cooling rate after sintering process. The aging treatment can promote the precipitation of α2 phase in α phase matrix and the silicide in β phase matrix. In particular, the precipitates prefer to be formed near the TiB whiskers by providing the nucleation sites. The solution and quenching treatment above the β transus temperature can gradually dissolved these precipitates with increasing solution time. Both the solid solution and the aging treatment can improve the tensile strength of them due to the formation of martensite α′ phase and precipitation of silicide and α2, respectively. The composites exhibit more sensitive effect of precipitates on the room temperature embrittlement than the monolithic Ti60 alloy.