Phase relation and transition in the Ti-Al-Mn system

Abstract

Seeking and optimizing beta solidified gamma (BSG) TiAl alloys have been recognized as hot research topics in recent few decades. Knowledge on phase equilibrium information including solubility limit and stability range can contribute to a necessary basis for tuning the performance of BSG alloys. In this work, we investigated phase relation and transformation in the Ti-Al-Mn system from 973 to 1373 K. With the increase of temperature, the β(Ti) phase region extends continuously accompanied by the change of Al solubility from 9.0 at% at 973 K to 34.7 at% at 1373 K. TiAl shows a wide composition range with the solubility of Mn increasing slightly along the temperature. A ternary Heusler phase β1 (Ti2AlMn) is confirmed to be stable below 1110.5 ± 12.5 K. And B2 phase with an island-like region exists in the temperature range of 1098–1123 K and can connect with Al-rich β(Ti) to form a whole as the temperature increases. According to the evolution of phase relations, two peritectoid reactions B2 + TiAl → Ti3Al + TiMn2 (1160.5 ± 12.5 K) and TiMn1−x + TiMn2 → Ti3Al + TiMn1+x (973–1023 K) can be defined. In addition, it was found that TiMn1−x can be stable up to 1373 K.