Effect of zero, normal and hyper-gravity on columnar dendritic solidification and the columnar-to-equiaxed transition in Neopentylglycol-(D)Camphor alloy

Abstract

Centrifugal casting is an important method to produce superior-quality cast parts. The microstructure and therefore materials properties strongly depend on the hyper-gravity level. To investigate the effect of gravity level on the solidification behavior, the transparent model alloy Neopentylglycol-(D)Camphor is used, which solidifies like metals. Its optical transparency allows for in-situ observation of columnar and equiaxed crystal growth. The experiments were carried out in a constant temperature gradient with two different cooling rates, and for g-levels ranging from zero-g in microgravity environment up to 10g0 on a centrifuge. It is found that the overall temperature and solutal fields close to the solidification front are not significantly altered by the laminar 3D melt flow in hyper-g environment. As a consequence, the growth velocity and primary spacing of columnar dendrites is nearly independent of the g-level. Increasing the cooling rate allows for nucleation and growth of equiaxed dendrites in the undercooled region ahead of the columnar solid-liquid interface. Here, at high g-levels the nucleation rate increases significantly and an accelerated, cascade-like settling of the growing equiaxed dendrites is observed. As a result, an earlier transition from columnar to equiaxed dendritic growth is detected in hyper-g environment.