Fracture mode transitions during indentation of columnar TiN coatings on metal

Abstract

Pyramidal indentations and focused-ion-beam machining have been used to study the damage during contact loading of textured columnar titanium nitride hard coatings on three steels and aluminium. The influence of the substrate hardness and coating thickness on the type and extent of fracture have been examined. In particular, the primary mechanism of deformation is shown to undergo a change from inter-columnar shear to other forms of subsurface damage. A physical model is proposed to explain this transition in the fracture mode. The implications of such behaviour for coating design are discussed.

Acknowledgements

Financial support for this work was made possible by grants from the Defense Research and Development Organisation, Government of India, and the Australian Research Council Discovery Grant Programme. The assistance of Dr Z.-H Xie of the School of Materials Science and Engineering, University of New South Wales, in preparing the FIB samples is gratefully acknowledged.