Structural and phase formation of TiAl alloys synthesized by mechanical alloying and heat treatment

Abstract

Mechanical alloying (MA) of Ti-50%Al (molar fraction) powder by using Planetary ball milling equipment, have been successfully refine the crystallite size and produced TiAl nano-alloys. The characteristics of the powder samples, including composition, surface morphology and microstructure, were investigated by using X-ray diffraction and field emission scanning electron microscopy (FESEM) coupled with Energy-dispersive X-ray spectroscopy (EDX). Mechanical alloying of elemental Ti and Al powder mixture resulting in the formation of Ti(Al) solid solution which exhibits a formation of TiAl phase after 40 h of milling. Crystallite size refinement by MA shows a great reduction from 70nm, down to minimum of 21nm after 100h of milling. Subsequent heat treatment of powder milled for 80 h exhibits the formation of a mixture of mainly α2-Ti3Al plus γ-TiAl phases. On the other hand, 100h milled powder exhibits the formation of a major γ-TiAl with α2-Ti3Al and a minor reflection of TiAl3 phases. The crystallite size of heat treated powder are varies and exhibits a grain growth after 40h of mechanical alloying process as a result of multiple phases formation.