【摘要】 采用微观相场模型,通过分析原子图像、有序相内序参数分布及有序相体积分数随时间的变化,在原子尺度对低Al浓度Ni75AlxV25-x合金的早期沉淀动力学进行了计算机预测.研究发现该合金沉淀过程中,析出D022结构的θ(Ni3V)相和L12 结构的γ’(Ni3Al)相,二者构成伪二元系;θ相先于γ’相析出,θ相的沉淀机制为等成分有序化+失稳分解,γ’相在θ相的相界处非经典形核,二者均先形成非化学计量比有序相,之后向化学计量比有序相转变;随Al浓度增加,θ相析出变慢,所占比例减少,而γ’相反之,析出越来越早且所占比例增加.更多还原

【Abstract】 The microscopic phase-field approach was used in modeling the early precipitation process of Ni75AlxV25-x alloy with lower Al concentration on an atomic scale through the simulation of atomic pictures, calculation of order parameter profiles and change of volume fraction of the ordered phases. The results show that D022 structured θ(Ni3V) and L12 structured γ(NisAl) ordered phases precipitated and formed a pseudobinary system; θ precipitated earlier than γ’ phase by a congruent ordering + spinodal decomposition (CO+SD) mechanism and thus produced a nonstoicheometric θ ordered phase, then the nonstoicheometric γ’phase precipitated by a non-classical nucleation and growth (NCNG) mechanism at the boundaries of θ phases, meanwhile, both of them transformed to stoicheometric ordered phases. With the increase of Al composition, the congruent ordering process of θ phase becomes more slow, and γ’ phase precipitation becomes earlier, the occupation percentage of γ increased and that of θ phase decreased.更多还原