Journal of Materials Processing Technology ( IF 6.3 ) Pub Date : 2022-01-19 , DOI: 10.1016/j.jmatprotec.2022.117506 Yaohong Xiao 1 , Zixuan Wan 2 , Pengwei Liu 3 , Zhuo Wang 1 , Jingjing Li 2 , Lei Chen 1
This paper provides a quantitative understanding of grain nucleation and growth at the interface of SS316L and IN625 bimetallic structures during directed energy deposition (DED) through multi-physics simulations, including phase-field models and computational fluid dynamics analysis. The main finding is that the flow behaviors would lead to composition redistribution and the change of liquidus temperature in the mixing zone at the interface, which further influences the solidification sequence and the final grain structure that are different from general single-metal counterparts without the mixing zone. The results show that during depositing IN625 on SS316L, a gradual transition in composition distribution and liquidus temperature in the well-mixing zone caused by simple clockwise flow leads to epitaxial grain growth from the SS316L substrate and the prevalence of columnar grains with a low undercooling (<1 K) condition. However, when depositing SS316L on IN625, it turns out that initial solidification can occur due to abrupt compositional change at the interface where the well-mixing breaks are caused by two opposite (clockwise and counterclockwise) flow behaviors. Such an abrupt compositional change results in high liquidus temperatures that may trigger the grain nucleation in the middle melt pool due to a high undercooling (>30 K); thus, a mixed grain microstructure is present.
中文翻译:
SS316L 和 IN625 的增材制造双金属界面晶粒成核和生长的定量模拟
本文通过多物理场模拟,包括相场模型和计算流体动力学分析,对定向能量沉积 (DED) 过程中 SS316L 和 IN625 双金属结构界面处的晶粒成核和生长进行了定量理解。主要发现是流动行为会导致界面混合区的成分重新分布和液相线温度的变化,从而进一步影响凝固顺序和最终晶粒结构,这与没有混合的一般单金属对应物不同区。结果表明,在 SS316L 上沉积 IN625 时,由简单的顺时针流动引起的混合区成分分布和液相线温度的逐渐转变导致 SS316L 衬底的外延晶粒生长以及具有低过冷度 (<1 K) 条件的柱状晶粒的普遍存在。然而,当在 IN625 上沉积 SS316L 时,结果表明初始凝固可能是由于界面处的成分突然变化而发生的,其中混合良好的破裂是由两种相反的(顺时针和逆时针)流动行为引起的。这种突然的成分变化导致高液相线温度,由于高过冷度(> 30 K)可能引发中间熔池中的晶粒成核;因此,存在混合晶粒微观结构。当在 IN625 上沉积 SS316L 时,结果表明初始凝固可能是由于界面处的成分突然变化而发生的,其中混合良好的破裂是由两种相反的(顺时针和逆时针)流动行为引起的。这种突然的成分变化导致高液相线温度,由于高过冷度(> 30 K)可能引发中间熔池中的晶粒成核;因此,存在混合晶粒微观结构。当在 IN625 上沉积 SS316L 时,结果表明初始凝固可能是由于界面处的成分突然变化而发生的,其中混合良好的破裂是由两种相反的(顺时针和逆时针)流动行为引起的。这种突然的成分变化导致高液相线温度,由于高过冷度(> 30 K)可能引发中间熔池中的晶粒成核;因此,存在混合晶粒微观结构。