Beyond Ni-base superalloys: Influence of Cr addition on Co-Re base alloys strengthened by nano-sized TaC precipitates

The high-temperature Co-Re alloy [1], a promising candidate for gas turbine applications, has a complex microstructure containing various kinds of precipitates in different size scales. The nano-sized fine spherical TaC (2Re₃ (σ phase) and Cr₂₃C₆ precipitates. In addition, Cr influences the temperature of the allotropic phase transformation of the Co matrix phase. It was found that additions of 5 at.% or 15 at.% Cr in the alloy does not result in the formation of Cr₂Re₃ and Cr₂₃C₆ phases. Further, the addition of such smaller amounts of Cr does not retain the Co γ (fcc) phase (stable or metastable) at room temperature after cooling from high temperatures. Only the ε (hcp) phase is present at low temperatures. The TaC precipitates are slightly influenced in size and volume fraction with 5 at.% and 15 at.% Cr.