时效工艺对Ni75Al15Ti10合金沉淀过程的微观相场模拟

Microscopic phase-field Simulation for the influence of aging process on the precipitation process of Ni75Al15Ti10 alloy

摘要:

本文通过微观相场动力学模型模拟了Ni₇₅Al₁₅Ti₁₀合金的沉淀过程。首先通过原子演化图发现,沉淀过程分为两步,起初为L1₀相向L1₂相的转变,随后为化学计量比L1₂相的形成。随后研究了单级时效温度对微结构,原子占位以及原子扩散的影响,结果表明：随着温度升高无规则形状的γ′相变为规则立方体状并且择优取向显著；同时Al原子从γ′相界面向内部扩散,Ti原子正好相反。但是温度越高,原子占位以及有序化程度越低。为了提高γ′相的原子占位,我们进一步比较了双级时效对γ′相的影响。发现双级时效不仅能获得规则排列稳定的γ′相,同时还可以提高Al与Ti原子在其正位处的原子占位并抑制反位缺陷的产生。我们的实验结果在一定程度上为制备具有优异力学性能的Ni-Al-Ti合金提供了理论依据。

Abstract:

The precipitation process of Ni₇₅Al₁₅Ti₁₀ alloy was simulated by microscopic phase-field kinetics model. The microscopic morphology evolution is firstly studied, which indicates that the precipitation process has been divided into two stages: the first is the transformation from L1₀ phase to L1₂ phase, the second is the formation of stoichiometric L1₂ phase. The effect of single aging temperature on the microstructure and atomic occupation probability and atomic diffusion are subsequently investigated. The result shows that the shape of γ′ precipitates is transformed from irregular shape to regular cuboid and the degree of orientation growth enhances with the increasing of aging temperature. But the higher aging temperature, the lower occupation probability and lower order degree. Meanwhile, the path of diffusion of Al is from the interface to the internal of γ" phase, and the diffusion of Ti atom is the opposite. Furthermore, we further study the dual aging with the purpose of improving occupation probability of γ′ precipitates and discuss its influence on the γ′ phase. Dual aging can not only obtain stable γ" phase with regular shape, but also can increase the occupation probability of Al and Ti and inhibit the formation of anti-site defects. Our results provide useful information in preparing Ni-Al-Ti alloy with excellent mechanical properties to some extent.