The residual stress generated in a superalloy during heat treatment affects the subsequent processing of the workpiece and may even adversely affect its performance. This paper investigates the effects of pre-stretching (in the range from 0% to 9%) before aging treatment on residual stress generated during quenching process and microstructure of Inconel 718 superalloy. After pre-stretching treatment, the residual stress deriving from quenching process can be well reduced. When the pre-stretch level was 3%, the quenching residual stress reached a maximum reduction of 72%, and the strength increased by 7.1%, while the product of strength and elongation hardly changed. Simultaneously, the microstructures of the pre-stretched specimens are observed by electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the fraction of high-angle grain boundaries in the alloy decreased while that of low-angle grain boundaries increased with increasing pre-stretch level. As the pre-stretch level was further increased to 9%, the proliferating entanglement of internal dislocations in the specimen was intensified, resulting in rod-shaped γ″ precipitates coarsening and volume fraction reduction of precipitates, which further led to a reduction in the product of strength and elongation of material.

中文翻译：

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预拉伸对Inconel 718合金残余应力和显微组织的影响

高温合金在热处理过程中产生的残余应力会影响工件的后续加工，甚至可能会对工件的性能产生不利影响。本文研究了时效处理前的预拉伸（在0％至9％范围内）对Inconel 718高温合金淬火过程中产生的残余应力和显微组织的影响。经过预拉伸处理，可以很好地降低淬火过程中产生的残余应力。当预拉伸水平为3％时，淬火残余应力最大降低了72％，强度增加了7.1％，而强度和伸长率的乘积几乎不变。同时，通过电子背散射衍射（EBSD）和透射电子显微镜（TEM）观察了预拉伸样品的微观结构。发现随着预拉伸水平的提高，合金中高角度晶界的分数降低而低角度晶界的分数升高。当预拉伸水平进一步提高到9％时，样品中内部位错的扩散缠结加剧，导致棒状γ''沉淀物粗大化，沉淀物的体积分数减少，从而进一步导致产物减少材料的强度和伸长率。