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 degrees C in the beta-phase field and different aging temperatures of 550-750 degrees 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 alpha+beta lamella (at 650-700 degrees C) and abnormal growth of alpha phase appeared (at 750 degrees C), which dominated the decreasing trend of microhardness and high-temperature strength. Besides, the silicides gradually precipitated along the prior beta phase and TiB whiskers (at 600 degrees C) as well as alpha/beta phase boundaries (at 650 degrees C). Eventually, 600 degrees C and 700 degrees 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 degrees C can obtain the highest 600 degrees C strength of 992 MPa, which is mainly attributed to martensite, precipitation of silicides and weak alpha(2) phase.