Nanoscale Depth Profiling of Residual Stresses Due to Fine Surface Finishing

Mechanical polishing is commonly used for both surface finishing and metallographic sample preparation for a broad range of materials. However, polishing causes local deformation and induces residual stress, which has an important effect on many surface phenomena. Until recently, it has not been possible to quantify the nanoscale depth variation of polishing-induced plastic deformation (eigenstrain) and the associated residual stress. In this study, the magnitude and depth of polishing-induced residual stress are evaluated directly by focused ion beam milling and digital image correlation using the micro-ring-core geometry method. Depth-resolved residual stress profiles are obtained with sub-micrometer resolution at the surface of a titanium alloy sample that is subjected to various polishing steps. It is found that electrochemical polishing and polishing with colloidal silica do not induce any significant residual stress. However, polishing with diamond slurry leads to the formation of compressive residual stresses of up to 300 MPa, which extend deeper into the material when larger diamond particles are used. This study paves the way for further research on polishing and its effect on surface properties.