Microstructure evolution mechanisms and strength improvement of (6.5 vol% TiC + 3.3 vol% Ti5Si3)/Ti6Al4V composites via heat treatments

To further improve the mechanical properties of titanium matrix composite containing relatively high fraction of TiC and Ti5Si3 particles, (6.5 vol% TiC + 3.3 vol% Ti5Si3)/Ti6Al4V composites were prepared at different sintering temperatures, and then were carried out heat treatments. The microstructure evolution and corresponding mechanical behavior of composites were investigated. It found that the aggregation of particles in composite was reduced with the sintering temperature increasing, while the size of particles was increased. During the quenching process, the Ti5Si3 particles dissolved into matrix and TiC particle played the role of preventing the growth of matrix. TEM and EBSD analyses revealed that the size of Ti5Si3 particles increased (from 50 nm to 300 nm) with the aging temperature increasing (from 700 °C to 900 °C), and growth mechanism of matrix transformed from boundary migration to grain coalescence, leading to the abnormal growth of matrix. 1200 °C sintered composite had the compressive yield strength of 1780 MPa and compressive strain of 21%. After 1200 °C solution treating followed by 800 °C aging treating, the yield strength increased to 1900 MPa without obvious decline of ductility. The improvement was attributed to the strengthening effect of particles.