Role of hydrostatic pressure and wall effect in solidification of TC8 alloy

Abstract

The solidification experiments of TC8 alloy under both microgravity and normal gravity were conducted using a drop tube. The solidification microstructure were found composed of fine equiaxed grains formed at early stage and bigger elongated grains formed at later stage. Between the two kinds of grains a curved transition interface was observed in 1g sample, while that in μg sample was almost flat. Generally, the amounts and aspect ratios of the grains are larger, and the grain sizes are smaller in 1g sample. Besides, no visible element macrosegregation occurred in both samples. The results suggest that the solidification velocities of the samples were rapid, and consequently the convection effect and solute transport effect caused by gravity had little influence on the solidification microstructure. Therefore, the solidification process was mainly controlled by thermal diffusion, and hydrostatic pressure and wall effect played a great role in it.

Effect of microgravity on the solidification of aluminum–bismuth–tin immiscible alloys

“…Microgravity is an excellent environment to inhibit the convection. 25–28 Since the 1970s, solidification experiments have been carried out under microgravity conditions of space to obtain immiscible alloys with a dispersed microstructure. For example, in 1978, Carlberg et al 29 performed solidification experiments with the Zn-Bi immiscible alloys on the second TEXUS flights and found that the phase macro-segregation occurs during the solidification.…”