Microstructural characterisation and thermal stability of in situ TiB 2 /60Si–Al composite synthesised by displacement reactions and spray forming

Abstract

A novel in situ reactive technique has been employed for preparing 2·0 wt-TiB₂/60Si–Al composite. The kinetic equations and the Arrhenius type equation were applied to compute the coarsening rate constant and the activation energy for grain growth for the composite when it was heated at semisolid state for partial remelting. Experimental results have shown that the in situ TiB₂ particles can refine effectively the primary Si phase and restrain the Si phase growth. The cubic coarsening rate constant for the composite was computed to be in the range of 75–148 μm³ min⁻¹ at temperatures in the range of 600–700°C, which was much less than that for the 60Si–Al alloy (1323–4523 μm³ min⁻¹). The value of activation energy for grain growth for the composite was about twice of that for the 60Si–Al alloy. The composite exhibited a higher thermal stability than that of the 60Si–Al alloy, suggesting that the in situ TiB₂ particles can effectively pin the grain boundaries and arrest the migration of liquid film in the semisolid state of the composite.