Microstructural Change during Sintering of Ti-45at%Al Mechanically Alloyed Powder

Abstract

The structure of a mechanically alloyed Ti-45at%Al powder and its decomposition behavior during sintering have been investigated by X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM). By the XRD experiments, the powder after 200 hr mechanical alloying is shown to be consisted of two phases, Ti₃A1 and TiAI. The volume fraction of Ti₃Al is estimated to be larger than that of TiAI, while for the sintered compact of the powder this tendency was reversed. The mechanically alloyed powder is composed of strain free fine grains (grain size ranging from 10 to 20 nm in diameter). The average composition of the grains are approximately Ti-45at%Al. Therefore, the powder may be assumed to be composed mainly of Al supersaturated Ti₃Al. The results of XRD and analytical TEM experiments suggest that the decomposition of the supersaturated Ti₃AI to equilibrium Ti₃Al and TiAI took place during sintering.