Characterization of subsurface micro-crack initiation in orthogonal cutting of nickel-based cast superalloy

The occurrence of subsurface micro-cracks during machining poses a significant challenge in manufacturing engineering, contributing to the degradation of components’ machined surface integrity. However, the process of micro-crack formation lacks direct in-situ experimental characterization, creating a gap in understanding the micro-crack initiation mechanisms on the machined subsurface. This study addresses this gap by utilizing an ultra-high-speed in-situ imaging system to capture micro-crack formation within the machined subsurface during the orthogonal cutting of nickel-based cast superalloy. The moment of crack initiation can be estimated by analyzing the displacement increment gradient between successive images. A quantitative analysis of displacement fields and accumulated strain fields during subsurface micro-crack initiation using the digital image correlation (DIC) approach has been presented. The localized tensile tangential strain on the machined subsurface before crack initiation is found to be approximately constant under various cutting parameters, and the maximum machined micro-cracks can reach around 59.7 μm in width and 158.6 μm in length. Furthermore, the observed cracking phenomenon in the machined subsurface demonstrates attributes typical of cleavage fracture, characterized by brittle cracking with low plasticity.