Transition metal aluminium nitrides produced by physical vapour deposition are widely used as hard, protective coatings in the manufacturing industries. To optimise coatings wear resistance while maintaining fracture toughness, an understanding of the mechanisms linking the microstructure and the orientation-dependent fracture behaviour is required. (V,Al)N coatings were synthesised by direct current and high power pulsed magnetron sputtering. Uniaxial compression testing was performed using micropillars oriented between 0° and 90° with respect to the growth direction to assess the effect of microstructure on the fracture behaviour. We show here that different fracture mechanisms are active depending on the alignment of grains and loading direction. The fracture behaviour could be divided into three classes associated with column buckling, decohesion or shearing and no significant difference between the specimens induced by the deposition process could be observed. Graphical abstract

No abstract

Since protective transition metal (oxy)nitride coatings are widely used, understanding of the mechanisms linking microstructure to their fracture behaviour is required to optimise wear resistance, while maintaining fracture toughness. To assess this interconnection, beam bending was performed using microcantilevers oriented parallel and at 90° to the growth direction. Furthermore, the tests were applied to favour normal bending and shear fracture. Coatings were synthesised by both direct current magnetron sputtering (DCMS) as well as high power pulsed magnetron sputtering (HPPMS). Here, we show that the fracture toughness depends on the alignment of the grains and loading directions. Furthermore, an improved fracture toughness was found in coatings produced by HPPMS, when microstructural defects, such as underdense regions in DCMS deposited coatings can be excluded. We propose indices based on fracture and mechanical properties to rank those coatings. Here, the HPPMS deposited oxynitride showed the best combination of mechanical properties and fracture toughness. Graphical abstract Principle of measuring the effects of microstructure and process route on the fracture toughness via microcantilever bending.