Titanium nitride/vanadium nitride alloy coatings: Mechanical properties and adhesion characteristics

This study examines the mechanical properties and adhesion characteristics of thin coatings of TiN, VN and various compositions in the Ti-V-N system deposited on stainless steel. Nano-indentation was used to determine the Young's modulus and hardness of the coatings. Tensile tests have been used to introduce controlled strains in the coatings, through the stainless steel substrate, to characterise the strength, fracture toughness and adhesion behaviour. The external stresses applied result in multiple cracking and localised delamination of the coatings, which have been followed in situ using optical microscopy. The Young's modulus shows a simple linear variation with composition within experimental error while the hardness and fracture properties show a clear maximum for the ternary alloy containing 23% VN. The Young's modulus behaviour can be explained by linear mixing while the maximum in the other properties may arise from optimum pinning of dislocations at Vanadium sites in the ternary alloys.