微观相场法研究镍基合金相变时的成分演化及界面定向迁移机制

Microscopic Phase-Field Study for the Evolution of Chemical Composition and Mechanisms of Directional Interface Migration during Phase Transformation for Nickel Based Alloy

基于耦合外应力场下的微观相场模型,研究了Ni_(75)Al_(7.5)V_(17.5)三元合金相变过程中相分解、生长过程中合金成分演化及应力作用下相间界面的定向迁移规律。研究表明:早期DO_(22)相长大所需的V来自于在L1_2相间有序畴界处,而后期则来自于其内部,且早期DO_(22)相长大的速度高于后期的长大速度;时效过程有5种异相间界面形成,而A类界面的迁移为相迁移的主要类型;相变初期A、B类界面较少,合金形貌变化不大,随着相变的进行,A类界面数量增加,相的生长及分解过程加剧,导致后期A类界面减少、B类界面增多,合金体系达到平衡状态;在压应力作用下,A类界面沿应力方向迁移,促进了DO_(22)相在此方向上的生长,导致合金"筏状"组织的形成。

Evolution of chemical composition during phase decomposition and growth and the mechanisms of the directional interface migration under exterior load for Ni（75）Al（7.5）V（17.5） alloy were investigated, which was based on a microscopic phase-field method. The results show that V the growth of DO（22） requires in the early stage comes from the ordering domain among L12, while it comes from the interior of L12 in the later stage, and the growth speed for DO（22） in the early stage is faster than that in the later stage. They form five types of interfaces, and A-type is the main type for interface migration. It has a few A and B type interfaces in the early stage, and morphology changes little. With the rise of the A-type interface number, the growth and decomposition for phases accelerate, the number of A-type interface declines and the number of B-type interface increases, and the alloy reaches balance finally. A-type interface migrates along the stress direction under compressive stress; as a result, DO（22） grows along this direction, and a rafting structure of the alloy forms.