Nanoscratch study of hard HfB2 thin films using experimental and finite element techniques

The response of HfB2 films to nanoindentation and nanoscratch was studied using both experimental and the finite element techniques. The material properties of HfB2 (elastic modulus, yield strength and Poissonʹs ratio) were derived by curve-fitting the simulated load–displacement (F–d) nanoindentation data with the experimental F–d data using a parametric analysis. Experimental results pertaining to both in situ and residual displacements were in good agreement with corresponding finite element results. As-deposited HfB2 films show significant plastic deformation, especially under high contact pressures (22.5 GPa), resulting in pile-up around the scratch area while annealed HfB2 shows appreciable elastic recovery. Annealing improves the propensity of the material to resist crack propagation (Mode 1) after scratch since annealed HfB2 shows appreciable reduction of residual tensile stresses as well as significant increase in residual compressive stresses compared to as-deposited HfB2. However, no such improvement is expected during scratch since in situ stresses do not differ significantly between as-deposited and annealed HfB2. The approach proposed and applied in this work to HfB2 films, is general and can readily be applied to other thin film materials. The proposed finite element model of nanoscratch could be valuable in predicting thin solid film performance.