Influence of the grain size of the alumina coating on crack initiation in indentation

摘要

A study has been made for indentation to the alumina coating on a cemented carbide substrate. Radial cracks initiate outside the contact circle on the surface of the coating and the critical load of crack initiation increases with the decrease of the thickness of the coating. It is demonstrated that the coating thickness can have a profound influence on the critical load of the radial crack initiation. An elastic-plastic analysis of indentation with a spherical indenter is also made by using the finite element method. The state of stress during indentation (including unloading) is investigated in detail. The tensile stresses, which might lead to crack initiation, are discussed intensively and examined by comparing with experimental results. The results indicate the grain size of the alumina coating is one of the important factors for crack initiation, reflecting the fact that the fracture strength of the coating depends on the grain size of the coating and decreases with increasing grain size.