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 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 phases, small ordered particles are observed in the Mn-containing alloy. Though Mn cannot hinder the formation of the ordered phases, the formation temperature of which is decreased to 600 degrees C. No ordered phases are observed in the Mo and Cr-containing alloys. Two percent of Mo and Cr hinder the formation of the ordered phases completely. The stabilization effect of Mn, Mo, and Cr on o phase is mainly a thermodynamic effect.