Surface morphologies and corresponding hardness evolution during nanoscratching

Abstract

Machining surface topography is a key factor affecting the properties of optical materials.It is generally accepted that the fracture mode tends to dominate practical concerns onmachined parts and the elastic recovery area decreases with the increase of normal load.However, material removal rate is low for ductile zone processing of brittle materials. In thiscase, pile-up and elastic recovery are key factors for surface quality. In this study, an accuratescratching and ploughing hardness model with consideration of both pile-up and elasticrecovery was established based on a series of continuous and constant nanoscratch tests.The hardness evolution mechanism under different nanoscratch deformation modes wasthen investigated. It was found that, in different modes, hardness values exhibited differentcharacteristics due to the change of elastic recovery rate and the intersection of elastic andplastic states. Further, the mapping relationship between hardness dispersion and surfacemorphology characteristics was also investigated. The results indicated that high degree ofhardness dispersion usually corresponded to modes I and II while stable hardness valuerepresented a steady plastic stage. Based on the intrinsic relationship between evolution ofhardness and deformation modes, predicting hardness distribution by in-situ testing dataand then adjusting deformation mode in real time would be helpful in optimizing surfacequality.