相场法预测低铝合金Ni_(75)Al_xV_(25-x)的早期沉淀过程

PREDICTION FOR THE EARLY PRECIPITATION PROCESS OF Ni_(75)Al_xV(25_x) SYSTEM WITH LOWER Al CONCENTRATION BY THE PHASE-FIELD MODEL

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.

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 D0(22) structured theta(Ni3V) and L1(2) structured gamma'(Ni3Al) ordered phases precipitated and formed a pseudobinary system; theta precipitated earlier than gamma' phase by a congruent ordering + spinodal decomposition (CO+SD) mechanism and thus produced a nonstoicheometric 0 ordered phase, then the nonstoicheometric gamma'phase precipitated by a non-classical nucleation and growth (NCNG) mechanism at the boundaries of theta phases, meanwhile, both of them transformed to stoicheometric ordered phases. With the increase of Al composition, the congruent ordering process of 0 phase becomes more slow, and gamma' phase precipitation becomes earlier, the occupation percentage of gamma' increased and that of theta phase decreased.