Effect of grain size on surface quality in single-point diamond turning of tungsten

Abstract

Tungsten and its alloys are representative difficult-to-cut materials extensively applied in plasma-facing components, where both surface integrity and subsurface microstructural features are critical. The purpose of this work is to investigate the machining mechanisms and quality associated with single-point diamond turning (SPDT) tungsten samples with distinct average grain sizes. Face-turning experiments were conducted to characterize surface morphologies, evaluate cutting forces, and examine subsurface microstructural evolution. In parallel, a FEA model incorporating the actual grain structure was developed to simulate stress propagation and distribution features during cutting. Results demonstrated that fine-grained tungsten specimen exhibited improved hardness because of Hall-Petch effect, resulting in more pronounced topographical variation and increased cutting forces. Nevertheless, the pre-existing grain and subgrain boundaries along with dislocations, were found to partially suppress surface micro-crack propagation. Furthermore, microstructural analysis identified the generation of a grain-refined layer, with grain widths reduced to a minimum of approximately 1 μm. The present research presents an in-depth insight into the influence of tungsten microstructural characteristics on its SPDT performance through the integration of experimental findings and grain-informed simulations.