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

Abstract

Prealloyed powders of the intermetallic ␥-TiAl phase and the ceramic -Ti 5 Si 3 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 ␥-TiAl crystals and -Ti 5 (Si,Al) 3 particles. Depending on the silicon content, these particles are interspersed within the grain boundary network of the ␥-TiAl phase or dispersed inside the ␥ 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.

Compaction of High-Energy Milled TiAlSi Powders by HIP: Simple Estimation of the Finest Grain Size Achievable in Fully Dense Materials

“…1). [12,13] Table 1. Careful density measurements revealed no influence of the applied HIP temperatures on the density of the compacts.…”

“…As the mean crystallite sizes of the c-TiAl phase and the n-Ti 5 (Si,Al) 3 phase show a fixed relation to each other, [12,13] independent of the applied HIP temperature, the estimation procedure described may also be performed for the c-TiAl grain size. The results would be the same.…”