Metal cutting involves the removal of material, typically accompanied by some form of fracture. However, the experimental observation of micro-crack formation during cutting presents a considerable challenge, leading to a gap in comprehending machined micro-crack initiation and propagation mechanisms. This study introduces an experimental methodology for thoroughly exploring the micro-crack formation process during the machining of nickel-based cast superalloy. Employing advanced tools, including an in-situ imaging system and digital image correlation (DIC) technique, the research quantitatively analyzes the cracking history on the machined subsurface during orthogonal cutting for the first time. Localized plastic deformation near the cutting tool tip and the inherent material heterogeneity contribute to crack initiation on the machined subsurface. The origin of these micro-cracks is primarily traced to Cr/Ti-rich carbides and Cr/Ti-rich sulfides located at the phase boundary between the large γ’ precipitate and the γ + γ’ matrix in the cast superalloy. Moreover, crack propagation during machining is proved to be a process involving both mode I (opening) and mode II (sliding) simultaneously. Quantitative differentiation of crack opening displacement profiles for each mode reveals a consistent increase with the augmentation of cutting tool edge radius, while the crack opening rate correlates positively with cutting speed and negatively with cutting tool edge radius. Furthermore, systematic strain field analyses under various cutting conditions reveal large-scale yielding during crack closure. These crucial findings significantly contribute to understanding materials processing, ensuring high surface integrity of components.

金属切削涉及材料的去除，通常伴有某种形式的断裂。然而，切削过程中微裂纹形成的实验观察提出了相当大的挑战，导致在理解加工微裂纹萌生和扩展机制方面存在差距。本研究介绍了一种彻底探索镍基铸造高温合金加工过程中微裂纹形成过程的实验方法。该研究采用包括原位成像系统和数字图像相关（DIC）技术在内的先进工具，首次定量分析了正交切削过程中加工表面下的裂纹历史。切削刀具尖端附近的局部塑性变形和固有的材料异质性有助于在加工的次表面上产生裂纹。这些微裂纹的起源主要归因于位于铸造高温合金中大的γ'沉淀物和γ + γ'基体之间的相界处的富Cr/Ti碳化物和富Cr/Ti硫化物。此外，加工过程中的裂纹扩展被证明是一个同时涉及模式I（张开）和模式II（滑动）的过程。每种模式的裂纹张开位移曲线的定量微分表明，随着切削刀具刃口半径的增大，裂纹张开位移曲线一致增加，而裂纹张开率与切削速度正相关，与切削刀具刃半径负相关。此外，各种切削条件下的系统应变场分析揭示了裂纹闭合过程中的大规模屈服。这些重要的发现极大地有助于理解材料加工，确保组件的高表面完整性。