Ni75Al4V21合金沉淀早期微观相场法模拟

采用三元体系微观相场动力学模型,对较低铝浓度的Ni₇₅Al₄V₂₁合金中γ′相和θ相沉淀早期进行计算研究,模拟了合金的原子图像演化过程,并计算了θ(Ni₃V)相和γ′(Ni₃Al)相的相内成分序参数分布和长程序参数分布.结果表明,θ相先析出,其沉淀机制为等成分有序化+失稳分解,等成分有序化产生非化学计量比的单相θ有序畴,并被相界分开,失稳分解为一特殊的分解类型,主要发生在相界处,形成化学计量比θ有序相;此失稳分解过程同时又是γ′相在θ相界处以非经典异相形核方式析出的过程,先形成非化学计量比γ′有序相,并逐渐长成为化学计量比γ′有序相,从而形成2种有序相共存的组织形态.

Simulation for early precipitation process of Ni75Al4V21 alloy by microscopic phase-field model

The microscopic phase-field kinetic model for ternary system was applied to investigate the precipitation process of γ′ and θ phase in Ni₇₅Al₄V₂₁alloy. The evolution of atomic pictures was simulated, and the composition and long-range order parameters of θ (Ni₃V) and γ′ (Ni₃Al) were calculated. The results show that θ forms earlier, its precipitation mechanism is congruent ordering followed by spinodal decomposition; By congruent ordering, a nonstoicheometric single θ ordered phase is produced with the order domains being separated by phase boundaries; Spinodal decomposition occurs predominantly at phase boundaries, and then the stoicheometric θ phase is formed; At the same time, γ′ (Ni₃Al) appears at phase boundaries of θ phase by nonclassical different phase nucleation mechanism, the nonstoicheometric γ′ phase forms earlier and gradually transforms into the stoicheometric γ′ phase, so two kinds of ordered phases appear simultaneously in the system.