Effect of Cr and Mn Addition on Microstructure Evolution and Tensile Properties of High Nb-TiAl Alloy

The variation of microstructure evolution, phase composition, solidification path and tensile properties of high Nb-TiAl alloys alloyed with fi stable elements Cr or/and Mn were studied. The results show that volume fraction of B2 phase gradually increases while alpha(2) phase gradually decreases in as-cast microstructures of Ti-45Al-8Nb-0.4B (atom fraction, %, similarly hereinafter) alloyed by 2Cr, 2Mn and ICrlMn. ICrlMn alloy turns into the novel beta-gamma high Nb-TiAl alloy, which is composed of gamma and B2 two phases rather than gamma, alpha(2) and B2 three phases. The solidification path changes from L ->beta+alpha ->alpha+gamma+beta ->alpha(2)+gamma+B2 to L ->beta ->beta+gamma -> B2+gamma. The co-addition of Cr and Mn has more obvious beta stable ability. The room temperature tensile results reveal that with the increase of B2 phase, the strength and elongation both decrease. While the elongation decreases firstly and increases subsequently at 900 degrees C. This phenomenon indicates that when the beta phase content reaches a certain level, which is 14.4% in this study, beta phase is advantageous to deformation at high temperature.