Phase Equilibria Among β/α/α2/γ Phases and Phase Transformations in Ti-Al-Cr System at Elevated Temperatures

Effects of Cr addition to TiAl alloy on the phase equilibria among beta/alpha/alpha(2)/gamma Phases and phase transformation pathways within the temperature range of 1.523 K similar to 1073 K were investigated using several alloys in the composition of interest. In between 1473 K and 1373 K. The slope of beta/alpha tie-line in the three-phase coexisting region of beta+alpha+gamma remains basically unchanged. However, this slope drastically rotates in a clockwise direction. in between 1373 K and 1273 K and below the eutectoid reaction temperature in the binary system (1400 K). This is a strong indication that alpha-phase exists even below the 1400 K. i.e. addition of Cr stabilizes a against alpha(2) and the three-phase coexisting region of beta+alpha(2)+gamma at lower temperatures is formed through a ternary eutectoid reaction (alpha -> beta+alpha(2)+gamma) with decreasing temperature. This threephase tie-triangle moves towards lower Al content in phase diagram. This suggests that Cr addition results in increase of the volume fraction of gamma-phase with decreasing temperature even in alloys with low Al content.