The main purpose of this study is to investigate the mechanical properties and micro-structures of IN718 super-alloy subjected to Cryogenic Treatment (CT). Tensile tests were performed and their engineering stress-strain curves were examined. Fracture morphologies of samples were observed with the help of Scanning Electron Microscopy (SEM). The micro-structural evolution of IN718 super-alloy before and after CT was investigated by both Optic Microscope (OM) and SEM. The composition of the precipitated phase was detected by Energy Dispersive Spectrometer (EDS). In order to better analyze the evolution of micro-structures, Transmission Electron Microscopy (TEM) observation was also carried out. Additionally, XRD technique was used to analyze the surface residual stress and microstructural phase. The results show that after two cycles of CT (CT-2), the tensile properties of IN718 super-alloy were found to be substantially improved at room temperature. Also, in comparison to the ductile fracture mode with very small dimples and some quasi-cleavage planes of untreated specimen, CT-2 specimen exhibited a more ductile fracture mode. The grains of CT-2 sample were significantly refined and the size became much more uniform. Compared to untreated specimen, the quantity of precipitated phases at grain boundaries was increased while the size of the precipitates was smaller and the distribution was more uniform after CT-2. High density dislocations were found to pile up at the grain boundaries. The occurrence of this phenomenon is expected to be explained as a result of micro plastic deformation and the increase of internal stress induced by volume shrinkage during the CT process.

这项研究的主要目的是研究经过低温处理（CT）的IN718超级合金的力学性能和微观结构。进行了拉伸试验，并检查了它们的工程应力-应变曲线。借助于扫描电子显微镜（SEM）观察到样品的断裂形态。用光学显微镜（SEM）和扫描电镜（SEM）研究了CT前后IN718高温合金的微观组织演变。通过能量分散光谱仪（EDS）检测沉淀相的组成。为了更好地分析微观结构的演变，还进行了透射电子显微镜（TEM）观察。此外，使用XRD技术分析表面残余应力和微观结构相。结果表明，经过两个周期的CT（CT-2），发现IN718高温合金的拉伸性能在室温下得到了显着改善。而且，与具有非常小的凹坑和一些未处理样品的准卵裂面的延性断裂模式相比，CT-2标本表现出了更大的延性断裂模式。CT-2样品的晶粒明显细化，尺寸变得更加均匀。与未经处理的试样相比，CT-2后晶界处的析出相数量增加，而析出物的尺寸更小且分布更均匀。发现高密度位错堆积在晶界处。预计这种现象的发生是由于微塑性变形和CT过程中体积收缩引起的内部应力增加所致。