Influence of matrix composition and MC carbide content on damage behaviour of TiN-coated high speed steel due to cyclic shear and compression load

Abstract

Hard-coated high speed steels are commonly used as tool materials for metal cutting applications, where they are exposed to a complex load spectrum consisting of shear and compressive stresses near the interface to the hard coating. These steels consist of different microstructural components, which on the one hand increase the stiffness of the material and on the other hand can withstand damage such as wear and cyclic plastic deformation. Although MC carbides are essential for the wear resistance and in particular can significantly increase the strength of the interface to the hard coating, knowledge about the influence of the steel microstructure on the cyclic damage behaviour caused by application-oriented load spectra is incomplete for these systems. Hence, this study focuses on the influence of coarse carbides and the martensitic matrix on the cyclic damage behaviour of TiN-coated high speed steels. Using an inclined impact test, a combined shear-/compressive load is applied to the steel/TiN interface of two different specimens with systematically varied high speed steel microstructures. Scanning electron microscopy on cross sections placed in the remaining imprints prepared by means of focused ion beam milling reveal a strong cyclic plastic deformation of the substrate that occurred after surpassing a critical applied force. Scanning electron microscopy and nanoindentation measurements in the high-speed steel matrix suggest cyclic softening and cyclic plastification, which is assumed to induce cracking at the interface between MC carbides and TiN coating.