Material removal mechanisms and characteristics of potassium dihydrogen phosphate crystals under nanoscratching

Potassium dihydrogen phosphate (KDP) crystals are important materials in high-energy laser systems. However, because these crystals are brittle and soft, machining-induced defects often emerge in KDP components. This study aimed to investigate the material removal mechanisms and characteristics of KDP during nanoscratching using Berkovich, spherical, and conical indenters. We found that KDP surface layers could be removed in a ductile mode at the micro/nanoscale and that dislocation motion was one of the main removal mechanisms. Removal characteristics are related to the stress fields generated by indenter geometries. The spherical indenter achieved a ductile removal mode more easily. The lateral force of nanoscratching increased with an increase in the normal force. The coefficient of friction (COF) followed the same trend as the lateral force when spherical and conical indenters were used. However, the COF was independent of the normal force when using a Berkovich indenter. We found that these COF variations could be accurately described by friction models.