Icosahedral quasicrystal enhanced nucleation in commercially pure Ni processed by selective laser melting

This work provides unambiguous evidence for the occurrence of icosahedral quasicrystal (iQC) enhanced nucleation during selective laser melting of gas atomized commercially-pure Ni powders. This solidification mechanism, which has only been recently reported in a few alloys and has to date never been observed in pure metals, consists on the solidification of grains of the primary phase on the facets of iQCs formed due to the presence of icosahedral short range order in the liquid. The occurrence of iQC enhanced nucleation has been inferred from the observation in the SLM processed pure Ni samples of an excess fraction of partially incoherent twin boundaries and of clusters of twinned grain pairs sharing common 〈110〉 five-fold symmetry axes. This work further evidences that additive manufacturing methods may constitute an invaluable tool for investigating the fundamentals of solidification and for the design of unprecedented grain boundary networks.