Primary spacing selection of constrained dendritic growth

Abstract

A transparent model alloy, succinonitrile-2.5wt% ethanol, was directionally solidified on a temperature gradient stage at constant, step-increasing or step-decreasing pulling velocity. The experimental results show that there exists a wide allowable range of primary spacing of dendritic arrays for given growth conditions; the upper limit and lower limit of the allowable range are very sharp, but average primary spacing is remarkably history-dependent. The upper limit, λ max, and lower limit, λ min, as a function of pulling velocity, V, can be expressed generally as λ max= aV -b and λ min= a'V -b' , where a, a', b and b' and b' are constant for given alloy and temperature gradient, and they decrease with increasing temperature gradient. The experimental results of the lower limit are in good agreement with the Warren-Langer model at high pulling velocities.