Synthesis of Intermediary Phases in Ti-Al-Si System by Reactive Sintering

Abstract

Reactive sintering as a simple and cost-effective method of preparation of bulk intermediary phases in the Ti-Al-Si system is presented. In this process, a pressed mixture of metal powders is transformed into the phases by thermally-activated chemical reactions. The alloys containing 10?20 wt.% of Si and 10?30 wt.% of Al were prepared by this technology. Pre-alloyed Al-Si powders are preferably used instead of Al and Si powders to improve the reactive sintering, reducing the product porosity. By optimization of the process parameters (temperature, heating rate, powder particle size), a porosity of less than 2 vol.% can be obtained. The material structure is formed by Ti₅Si₃ particles in the TiAl or Ti₃Al matrix. The kinetics of the process is controlled by the formation of an intermediary phase. The materials exhibit very high hardness (up to 800 HV 10) due to hard Ti₅Si₃ particles. The oxidation stability of the materials at high temperatures is comparable with that of commercial Ni-based alloys, but is much better than that of Ti-Al alloys.