Simulation of Columnar Crystal Growth in Forced Flow of VAR Based on Phase Field Method

Abstract

A fully coupled flow heat mass model was established based on the phase field method to simulate the growth of columnar crystals in ingots during vacuum arc remelting （VAR） in a forced flow field. The influence mechanism of melt flow on the growth of columnar crystals was analyzed by comparing the growth characteristics of columnar crystals with and without flow field conditions.The simulation results indicated that when the velocity of flow field in the solidification front is 45 μm/s and the direction is perpendicular to the direction of dendrite growth， the secondary dendrites exhibit ‘counter-flow’ growth， and the dendrite trunks tilt downstream due to erosion. A small eddy current is formed between adjacent dendrites， and the solutes and the heat in the upstream of the dendrite trunks are carried into the downstream side with the melt. The boundary layer thickness of the solute and the temperature on the upstream side decreases， from 51 μm in the absence of a flow field to 31.5 μm. The large temperature gradient promotes the development of secondary dendrites. The concentration of solutes and heat in the downstream boundary layer is high， and the boundary layer thickness increases to 78 μm. The decrease in gradient significantly inhibits the development of secondary dendrites. The downstream solute concentration is higher than that in the absence of a flow field， and the slow growth of dendrites increases the risk of micro-segregation.

Keywords

• vacuum arc remelting； phase field； columnar crystal growth； forced flow field； solute field； temperature field