Submicron-grained multiphase TiAlSi alloys: Processing, characterization, and microstructural design

Abstract

Prealloyed powders of the intermetallic γ–TiAl phase and the ceramic Ξ–Ti5Si3 phase were high-energy milled and hot-isostatically pressed (HIP) to produce silicide dispersed composite materials with grain sizes in the submicron and nanometer range. The amorphous state of the as-milled powders crystallizes via a multistep decomposition reaction during degassing at 440 °C and HIP. At a pressure of 200 Mpa HIP-temperatures as low as 750 °C are sufficient for a complete densification of the milled powder. The microstructure of the compacts is very homogeneous and consists of equiaxed γ–TiAl crystals and Ξ–Ti5(Si,Al)3 particles. Depending on the silicon content, these particles are interspersed within the grain boundary network of the γ–TiAl phase or dispersed inside the γ grains. With respect to technical applications, submicron-grained composites are regarded as promising precursor materials that should allow for easy hot working in the as-prepared state as well as for high-temperature structural applications after a suitable transformation of the microstructure.