GH4169合金高温动态应变时效实验及模拟

Experimental and modeling investigations of high temperature DSA behaviour for GH4169 superalloy

摘要:

为了解和掌握GH4169高温合金热处理过程中动态应变时效（dynamic strain ageing, DSA）现象对力学性能的影响,通过高温单轴拉伸实验及数值模拟的方法对固溶态该合金高温条件下DSA现象进行了实验及模拟研究.不同应变率的单轴拉伸实验在620 ℃的高温下进行,应变速率分别为10^-2、10^-3、10^-4 s^-1.实验结果表现出了由DSA效应导致的负的应变率敏感性,以及明显的锯齿状屈服现象.基于热激活能的塑性流动法则并对DSA效应予以明确考虑,建立了材料宏观一维本构模型,其中变形阻力被分为位错滑移阻力及DSA效应导致的变形阻力两部分,DSA效应模型中引入等效时效时间及等效热激活等待时间两个内变量,通过最小二乘法进行参数拟合.该本构模型的计算结果与实验结果具有较高的一致性. 结果表明,通过分析本构模型中内变量的变化趋势得出结论,位错滑移阻力随应变速率的提高表现出上升趋势,而DSA效应导致的变形阻力随应变率的提高表现出下降趋势. 因此,材料强度在一定应变率范围内的应变率负相关现象是由于DSA效应及正的率效应两种机制之间的竞争所导致.

Abstract:

To understand the influence of the dynamic strain ageing (DSA) phenomenon on the mechanical properties of GH4169 superalloy during heat treatment, experimental and modeling investigations of DSA were carried out for solid solution treated nickel-based GH4169 superalloy at elevated temperature. Uniaxial tensile tests at 620 ℃ with strain rates of 10^-2, 10^-3, and 10^-4 s^-1 were performed to characterize the DSA effect, and negative strain rate sensitivity and serrated yielding behaviours were identified. Through the use of a thermal activation based viscoplastic flow rule with the DSA effect incorporated, a one-dimensional constitutive model was established. The deformation resistance was divided into two parts, i., slip resistance and deformation resistance caused by DSA effect. Two internal variables, equivalent ageing time and waiting time, were introduced to describe the DSA effect, and a least-squares method was adopted for parameter fitting. Comparison show that the calculated results of the constitutive model were in good agreement with the experimental results. The slip resistance increased with the increase of strain rate, whereas the deformation resistance caused by DSA effect decreased with the increase of strain rate. It further indicates that the identified negative strain rate sensitivity is the result of the competition between DSA effect and normal rate effect in certain strain rate range.