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

Abstract 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. Graphical abstract Image 1 Highlights • Effect of Hf on annealing twin formation in a nickel-based superalloy was studied. • With adding 0.3 wt.% hafnium, the annealing twin boundary fraction is decreased. • Minor addition of hafnium yields increased amounts of MC carbides. • MC carbides could effectively lower the annealing twin nucleation probability. • MC carbides could effectively impede the growth of annealing twin into grains. [ABSTRACT FROM AUTHOR]