Gas formation during reaction sintering of titanium aluminides

Abstract
Titanium aluminides are attractive materials not only for aviation and space research but also for application in automotive engines. Reaction sintering of titanium aluminides involves considerable swelling during phase formation ; the reason for this effect has not been understood until now. A strong increase of porosity is connected with this swelling of the samples, which must be avoided by using expensive HIP techniques. The influence of gas reactions on the swelling is investigated by mass-spectrometric analysis of the gases produced during reaction sintering. By means of simultaneous measurements of mass change (thermobalance), enthalpy change (DTA) and gas production (quadrupole mass-spectrometer) in dependence on temperature significant information on the course of the reaction sintering process is found. Espescially it is possible to determine the generation of hydrogen and gaseous water during the heating process and to correlate them to the swelling effects. From these results conclusions may be drawn for an optimization of the sintering parameters during reaction sintering of titanium aluminides.