Microstructure evolution and enhanced mechanical properties of as-rolled TiB/(TA15-Si) composite via heat treatment

To improve the mechanical properties of the as-rolled composite under large rolling deformation, the effect of solid solution and aging on the microstructural characteristics and mechanical properties of the as-rolled TiB/(TA15-Si) composite was detailedly investigated. The solid solution temperatures of 1050 °C in the β-phase field and different aging temperatures of 550–750 °C were chosen to regulate the evolution of matrix and silicides. After solid solution treatment, the matrix transformed from elongated and kinkled lamella into acicular martensite microstructure. And the silicides completely redissolved into matrix and a uniform diffusion of Si atom was presented. Meanwhile, the aging temperature can obviously affect the evolution of martensite and silicides. As aging temperature increased, the martensite gradually decomposed into acicular α+β lamella (at 650–700 °C) and abnormal growth of α phase appeared (at 750 °C), which dominated the decreasing trend of microhardness and high-temperature strength. Besides, the silicides gradually precipitated along the prior β phase and TiB whiskers (at 600 °C) as well as α/β phase boundaries (at 650 °C). Eventually, 600 °C and 700 °C strengths of the as-rolled composite can be obviously improved by 39.7 % and 84.6 % after solid solution and aging processes. And the composite aged at 600 °C can obtain the highest 600 °C strength of 992 MPa, which is mainly attributed to martensite, precipitation of silicides and weak α2 phase.