材料期刊网

采用相场模型定量模拟了动力学各向异性作用下过冷熔体中的晶体生长过程.模拟结果表明,仅存在动力学各向异性时,各向异性系数大小对生长方式选择起着决定性作用.当各向异性较低时,固相以分形方式生长,在生长过程中不存在占优势的生长方向,同时也不存在稳态生长状态;而当各向异性系数大于0.02时,固相以枝晶方式沿<110>方向生长.进一步研究表明,枝晶生长稳定性系数随各向异性值的增加而增加,而与动力学系数取值无关.

Solidification is generally determined by a complex interplay of heat and/or solute diffusion processes, capillary and/or kinetic effects of the solid/liquid interface. Theoretical analysis indicates that the crystal growth morphology and behavior both depend sensitively on the degree of the capillary and kinetic anisotropy. In present, the influences of capillary anisotropy on crystal growth process have been extensively studied, especially simulated by the phase-field model. Unfortunately, the influences of kinetic anisotropy on the crystal growth morphology and behavior are seldom re-searched. In this paper, the phase-field model was employed to quantitatively simulate the effects of kinetic anisotropy on the crystal growth in undercooled melts. It is illustrated that the selection of the solid/liquid interface morphology is determined by the kinetic anisotropic parameter if the capillary anisotropy is set as zero. With a weak kinetic anisotropy, the melt solidifies in a fractal pattern, during which there is no obvious preferred growth direction, and any steady-state growth cannot be detected. As a strong anisotropy becomes greater than 0.02, the interface morphology changes to a dendritic pattern growth along the <110> orientation. Further analysis indicates that the stability parameter increases linearly with the increase of kinetic anisotropic parameter and is independent of the kinetic coefficient.