Abstract
Stoichiometric mixtures of titanium hydride and atomized aluminum powders for TiAl are pressed uniaxially into compacts, 10mm×10mm×10 or 5mm in size, and sintered in argon.
Differential thermal analysis curves demonstrate the decomposing endothermic reaction of the titanium hydride into titanium and hydrogen, and exothermic synthesizing reactions of compounds. The synthesizing reactions begin before the exothermic peak in a DTA curve and proceed through the peak. A subsequent holding at a high temperature for a long time is necessary in order to complete homogenization. The exothermic peak appears immediately after the melting of aluminum. The peak is attended with a rapid decrease in density of the compact. A subsequent heating to higher temperatures gives rise to a slow densification. Both swelling and shrinkage appear earlier in the compacting direction than in the lateral one.
The slower is the heating rate in the reaction temperature range, the less are the swelling and the anisotropic dimensional change. The finer particle size gives less swelling and anisotropy in dimensional change and more densification and independency of heating rate.
