Epitaxy and new stray grain formation mechanism during epitaxial laser melting deposition of Inconel 718 on directionally solidified nickel-based superalloys

The epitaxy behavior and stray grains (SGs) formation in the deposit during epitaxial laser melting deposition (E-LMD) of directionally solidified (DS) superalloys were investigated. Columnar dendritic structures were obtained by epitaxial solidification on the DS substrate. The deposit also remained the orientation of the substrate. The SGs at the fusion interface, which were hardly eliminated, were attributed to different SGs formation mechanisms. The SGs were divided into GB-SGs and MC-SGs by the distribution characteristics. The GB-SGs at the low-angle and high-angle grain boundaries with a new mechanism of dynamic recrystallization induced by accumulation of thermal strain and stress under repeated spatially variable heating and cooling. The MC-SGs around the carbides were related to the misoriented cellular crystal formation caused by the varied shape of the solid-liquid interface. The columnar to equiaxed transition (CET) was another mechanism of MC-SGs formation.