Behavior of Ti0.5Al0.5N thin film in nanoscale deformation with different loading rates

Artikel i vetenskaplig tidskrift, 2008

The nanostructured solid solution Ti0.5Al0.5N thin film (similar to 1.2 mu m in thickness) was prepared on Si (100) substrates by reactive close-field unbalanced magnetron sputtering at a bias voltage of -50 V in an Ar-N-2 gas mixture. The deformation behavior of the film was systematically investigated by nanoindentation measurements. Analyses of the obtained load-displacement curves showed no evidence of a "staircase" discontinuity in the specimen and the effect of the tip radius of the indenter on the behavior of elastic and plastic deformation can be determined. The critical shear stress, yielding strength and the size of plastic zone of the Ti0.5Al0.5N thin film under nanoindentation were evaluated by integrating the Hertzian stress analysis and the Johnson's cavity model. Results revealed that the new complete dislocation nucleation during indentation was not the prerequisite for the onset of plastic deformation, which met Von Mises yielding criteria. The relationship between the normalized plastic zone size and loading rates was also established. It was suggested that the ability of plastic deformation of the Ti0.5Al0.5N thin film under nanoindentation was sensitive to the loading rates, which is attributed to the metastable crystalline structure of thin film.