A study on the effect of composition, and the mechanisms of recrystallisation in single crystal Ni-based superalloys

The effect of composition on recrystallisation of single crystal Ni-based superalloys was studied in a series of alloys that vary systematically in composition. Following room temperature macro-indentation and subsequent annealing, alloys containing higher Co concentration showed greater susceptibility to recrystallisation, and this has been attributed to the effect on the γ′ solvus temperature and the stacking fault energy of the γ phase. Mo, W and Ru did not appear to influence the recrystallisation behaviour systematically, although high concentration of all these elements led to the highest recrystallisation. Moreover, with grain orientation mapping, it was found that the nucleating recrystallisation grains form in orientations similar to the deformed regions, and subsequently twin to form higher angle boundaries and proliferate further within the deformed microstructure. The effects of the interaction between grain boundaries and secondary phases, such as the γ′ and topologically close packed phases, were also studied