Computational fluid dynamics calculations of binary representation of Ni-base superalloy solidification in frustum geometries

Abstract

CFD calculations were carried out on a number of frustum geometries from the experimental literature on freckling of superalloys. The effects of two imposed thermal fields were investigated, flat and inclined. Experiments document that when thermal fields are inclined the cold side is more prone to formation of freckles; our results conclude that rising liquid plumes in advance of the solidification front, which can correlate to freckles, are more abundant and intense on the cold side. Also, modelled plume activity is greater in inward sloping frustum geometries as opposed to outward sloping ones, which also agrees with established literature. Complex flow patterns were observed in inclined geometries and there is a clear interplay and competition between both the thermal and solutal aspects of flow, with flow being significantly changed, sometimes reversed in direction in some capacity. Our results also offer insight into the incubation length for plume and resultant freckle formation after the transition between frustums, with some critical distance of advance of the solidification front necessary to initiate and establish other plumes that feed into the main one circulating liquid flow which is locally intense enough to potentially create a freckle.