Effect of hafnium on annealing twin formation in as-hot isostatically pressed nickel-based powder metallurgy superalloy

The effect of hafnium on the microstructure of as-hot isostatically pressed nickel-based powder metallurgy superalloy FGH4097 has been investigated. It is shown that when adding 0.3 wt.% hafnium, the statistical annealing twin boundary length fraction of the hafnium-free superalloy decreases from 0.35 ± 0.01 to 0.30 ± 0.01 and its interaction events of annealing twins are considerably reduced. The main reason is found to be the increase of MC (where M = metal atom) carbide density caused by micro-addition of hafnium, which could effectively lower the annealing twin nucleation probability and impede its growth into grains by retarding the movement of Shockley dislocation in the end of non-coherent twin boundary.