Production of fully dense (α2+γ) TiAl by reactive hot isostatic pressing (RHIP) of an elemental powder mixture

Elemental powder mixtures of Ti-48at%Al were consolidated by Reactive Hot Isostatic Pressing (RHIP) at 800 degreesC, 1100 degreesC and 1250 degreesC/180MPa/2h. The canned cold isostatic pressed mixtures were previously degassed by heating up at a rate of 5 degreesC/min. up to 450 degreesC in vacuum. Based on differential thermal analysis (DTA) results, the relative sizes of the Ti and Al powders used and the heating rate for RHIP were chosen so that the exothermic reaction to form the precursory TiAl3 took place in the solid state. The consolidated materials microstructures were evaluated using optical and scanning electron microscopy. RHIP at 800 degreesC resulted in a compact which was incompletely reacted and still porous, while after RHIP at 1250 degreesC, a fully dense (alpha (2)+gamma) duplex structure resulted. Subsequent heat treatments at 1000 degreesC resulted in stabilization of this structure and decreased the lamellar/equiaxed grains volume ratio.