Inhibition of ωo phase precipitation in TNM-based TiAl alloys by Cr and Mn

Abstract

In modern β-solidified γ-TiAl alloys, ωo phase usually precipitates very easily within βo phase during heat treatment at intermediate temperatures. This phase transformation leads to increased brittleness and reduced service performance of the alloy. In this paper, the evolution of the ωo phase is investigated in the TNM-based TiAl alloys by the addition of Mn or Cr elements. The results show that both Mn and Cr have a strong inhibiting effect on the precipitation of ωo phase, while the inhibiting effect with Mn addition is more obvious. Specifically, in the Ti-43.5Al–4Nb-0.6Mn-0.1B alloy exposed to 750 °C for 1000 h, the ωo phase is almost completely inhibited. The composition range in which Mn and Cr effectively suppressed the ωo phase precipitation were determined by reasonable modulation. The phase transformation temperature of ωo phase was lowered by the addition of alloying elements, making it difficult to precipitate at intermediate temperatures. The corresponding phase transformation mechanisms were discussed.