Densification of rapidly solidified titanium aluminide powders—I. Comparison of experiments to hiping models

Abstract

Rapidly solidified γ-titanium aluminide powders were characterized and subjected to consolidation by hot isostatic pressing (HIP). Primary solidification of h.c.p.-α phase followed by formation of interdendritic γ-segregate prevails in both REP (Ti-50% Al-1.8% Nb) and RSR (Ti-48% Al-2.4% Nb-0.3% Ta) powders, except for a minor fraction of fine powders that form b.c.c.-β phase from the liquid. The evolution of these microstructures and their subsequent solid state transformations are in line with previous observations on binary titanium aluminide droplets solidified with and without supercooling. In the consolidation experiments, the influences of time, temperature and pressure on final densification were experimentally determined and compared with predicted HIP maps using best estimates of input data on material properties. Experimentally it was found that the densification rate is independent of average mean particle diameter. Best agreement between predictions and experiments were obtained for power-law creep as the dominant consolidation mechanism at high pressure, i.e. 182 MPa. Modifications of the model are suggested for consolidation during the pressurization.