Multiscale Damage Mechanisms of Polycrystalline Diamond During Mechanical Polishing

Polycrystalline diamond (PCD) is widely used in semiconductor, optical, and thermal applications, where achieving a damage-free surface is essential. However, controlling surface/subsurface damage (SSD) remains a fundamental challenge during free-abrasive mechanical polishing (MP) of PCD. Specifically, it is unclear how the interplay between grains, grain boundaries (GBs), and abrasive–workpiece. To address this knowledge gap, an integrated approach combining MP experiments, tribological testing, and molecular dynamics (MD) simulations was developed to tackle this problem. Through this combined methodology, this study presents an insight into understanding of how these processes occur in PCD during polishing. Accordingly, the thresholds for SSD evolution with respect to abrasive size and applied load are determined. The abrasive size primarily defines the roughness range, while the applied pressure controls the extent and severity of subsurface deformation and amorphization. Importantly, we demonstrate how microscale characterization provides critical feedback into the polishing process, revealing how GBs act as both stress concentrators promoting amorphization and barriers preventing intergranular stress transfer. These findings directly link microscale damage mechanisms to the macroscopic polishing outcomes, highlighting how process parameters influence subsurface damage evolution. The MD simulations not only explain key experimental observations, such as sp³ to sp² transitions, stacking fault formation, and GB-mediated crack deflection, but also provide dynamic insights into atomic-scale processes, confirming that GBs play a crucial role in SSD evolution. This study provides a solid scientific foundation for deciphering PCD polishing and optimizing process parameters to minimize SSD during free-abrasive polishing.