Alloying Effects on the Phase Transformation Behaviors of the Orthorhombic and Ordered ω Phases in High Nb–TiAl Alloys

In this work, alloying effects of Mn, Mo, and Cr on the phase transformation behaviors of the orthorhombic and ordered ω phases in high Nb–TiAl are investigated. Modulated structures are observed in the Mn and Mo-containing alloys indicating that Mn and Mo cannot hinder the formation of the orthorhombic phase while Cr hinders the formation of the orthorhombic phase completely. For the ordered ω phases, small ordered ω particles are observed in the Mn-containing alloy. Though Mn cannot hinder the formation of the ordered ω phases, the formation temperature of which is decreased to 600 °C. No ordered ω phases are observed in the Mo and Cr-containing alloys. Two percent of Mo and Cr hinder the formation of the ordered ω phases completely. The stabilization effect of Mn, Mo, and Cr on βo phase is mainly a thermodynamic effect.