Ni-Al合金中Ni_3Al相沉淀过程的微观相场模拟

MICROSCOPIC PHASE-FIELD SIMULATION FOR Ni_3Al PRICIPITATION IN Ni-Al ALLOY

基于微观相场动力学模型和微观弹性能理论,对Ni-Al合金中沉淀相Ni_3Al(γ′)形貌演化、早期沉淀机制和后期粗化过程进行了原子层面的计算机模拟．结果表明:沉淀过程中γ′相形貌由早期随机分布的圆形或不规则状逐渐向方形转变,其排列的取向性也越来越明显,最后形成周边圆滑的长方块状颗粒,沿[10]和[01]弹性“软”方向规则排列．弹性应变能作用下的粗化过程遵循优先选择的原则,位于弹性“软”方向上的颗粒不断长大和粗化,位于弹性“软”方向外的颗粒逐渐消失,沉淀后期在基体中形成高度择优取向的微观组织．低浓度Ni-Al合金中γ′相的早期沉淀机制为非经典形核长大机制,其演化序列为:过饱和固溶体→非化学计量比有序相→化学计量比平衡γ′相→长大．

Based on the microscopic phase--field dynamic model and the microelasticity theory, the morphology evolution of Ni3Al （γ′） phase and early precipitation mechanism in Ni-Al alloy were simulated. Simulation results show that γ′ phase morphology changes from initial circular or irregular shape into the quadrate shape and their orientations become more obvious during precipitation process, in the later stage, the γ′precipitates present quadrate shape with round corner and regularly align along the [10] and [01] directions. Under the effect of elastic strain energy, the coarsening process follows the rule of preferential selection, the particles lying in the elastic soft directions grow and coarsen further; the particles lying out of the elastic soft direction shrink and dissolve, highly preferential selected microstructure is formed in the later precipitation process. The early precipitation mechanism is the non-classical nucleation and growth, the evolution of γ′ phase is in the order： supersaturated solid solution→nonstoicheometric ordered phase→ stoicheometric γ′phase→growth.