Elastic-plastic deformation and cracking behavior of thin hard chromium-based coatings

Physical vapor deposition (PVD) is a commonly applied technology for deposition of hard coating systems such as chromium (Cr)-based nitrides and oxynitrides on tools and components. In tribological applications, the tools and components are subjected to complex loading situations. This can lead to elastic-plastic deformation of the protective coatings and coating/substrate compounds or hard fracture response followed by crack formation. Thus, it is imperative that knowledge and understanding of the mechanical response be developed, to provide quality and reliability assurance for conditions representing those dictated by actual service applications. The subject of this thesis was to develop a comprehensive understanding of the elastic-plastic deformation and cracking behavior of thin hard Cr-based nitride and oxynitride coatings. Both static and dynamic loadings were employed. Besides the established investigation methods, several experimental and simulative approaches were developed and applied, which enable both qualitative and quantitative analyses. Firstly, the influence of coating's architecture on its elastic-plastic deformation behavior was studied. Thereafter, the effects of incorporating aluminum and oxygen into the coating system on the deformation and cracking behavior of coatings and coating/substrate compounds were investigated. The influence of oxygen content was subsequently studied using three oxynitrides having different oxygen contents. Furthermore, comprehensive analyses were conducted on plasticity, which lead to the understanding of the underlying mechanisms for the plastic deformation of the thin hard Cr-based coatings. Finally, the influence of the coating's residual stress on the cracking behavior was studied using a finite element method.