Estimation of fatigue life of TiN coatings using cyclic micro-impact testing

Abstract: This paper studies the behaviour of a thin titanium nitride (TiN) coating (1.5 um thick) on a tool steel substrate material under dynamic and cyclic impacts through an approach combining experimental testing and computational modelling. Dynamic impact testing was used to investigate the load-dependent dynamic hardness and assess the energy-dissipation capabilities of the coating system. In cyclic impact tests, the materials experienced permanent plastic deformation in each cycle, ultimately leading to coating failure. Chemical analysis identified an interlayer between the coating and the substrate, while cross-sectional analysis revealed the extent of coating damage due to cycling and impact load. A three-dimensional map was constructed, connecting the acceleration load, sensed depth, and cycles to the coating failure, and an empirical equation used to characterize the relationship between the depth and cycles to failure. The computational model examined the traction component distribution during loading and unloading, with a focus on normal and shear tractions. These findings suggested the potential significance of normal traction in the interfacial fatigue failure due to impact.