Abstract:

The experiment of varied cutting-depth nanoscratching for K9 glass is carried out on nano indenter system by Berkovich indenter. To explore the relationship between the friction coefficient and depth of brittle-to-ductile transition, the equation of the normal force and tangential force on the depth are fitted based on nonlinear least square method, which is tested by the correlation coefficientr. The surface morphology of groove is analyzed by AFM and SEM, which find that there are three regimes(elastic-plastic transition regime, plastic removal regime and brittle fracture regime) in scratching process. The depth of elastic-plastic transition for K9 glass is obtained based on Hertz contact theory. According to the results of AFM and SEM, the critical depth of brittle-to-ductile transition is obtained with regarding the first crack as brittle-to-ductile transition point. Based on the depth of brittle-to-ductile transition, the characterization method of brittle-to-ductile transition proposed by WEI is improved by adding the correction factor. The new characterization method of brittle-to-ductile transition for K9 glass is established by the friction coefficient. By analyzing the generation of friction zone causing by the friction of indenter and workpiece in scratching process, the generation of cracks and the angle between the direction of crack and the scratching direction which is about 60° are explained.

Key words: ductile-to-brittle transition, K9 glass, removal characteristic, varied cutting-depth nano-scratch