Ceramic nitride/metal coatings with enhanced fracture toughness and fatigue resistance using a multiscalar laminate architecture

Ceramic coatings can provide benefits such as improved wear resistance, reduced friction, and be chemical and biological corrosion barriers in various biomedical applications. However long-term issues of film cracking, particle generation, or delamination must be addressed, while achieving decades-long coating lifetimes. Instead of brittle, superhard coatings, softer but tougher coatings achieved with multiscalar, laminate architectures may meet these requirements. Layers of Cr and CrN were combined in multi- and nanolayer structures, and compared to monolayer films. The multiscalar coatings had hardness values lying between the pure Cr and CrN, but higher fracture toughness than the monolayer films

Comparison of the Dislocation Structure of a CrMnN and a CrNi Austenite after Cyclic Deformation

In the literature, the effects of nitrogen on the strength of austenitic stainless steels as well as on cold deformation are well documented. However, the effect of N on fatigue behaviour is still an open issue, especially when comparing the two alloying concepts for austenitic stainless steels—CrNi and CrMnN—where the microstructures show a different evolution during cyclic deformation. In the present investigation, a representative sample of each alloying concept has been tested in a resonant testing machine at ambient temperature and under stress control single step tests with a stress ratio of 0.05. The following comparative analysis of the microstructures showed a preferred formation of cellular dislocation substructures in the case of the CrNi alloy and distinct planar dislocation glide in the CrMnN steel, also called high nitrogen steel (HNS). The discussion of these findings deals with potential explanations for the dislocation glide mechanism, the role of N on this phenomenon, and the consequences on fatigue behaviour