Investigation of deformation behavior under different loading directions in transition metal (oxy)nitride thin films
The aim of this project was to study the effect of transition metal species and the presence of oxygen on the mechanical properties of transition metal (oxy)nitride films, and in doing so to link quantum and continuum mechanics for material design. The growth of these films results in a strongly columnar microstructure, so it is necessary to understand the influence of this texture on mechanical properties.
Uniaxial compression was thus performed using micropillars in samples of varying compositions as well as at different angles to the growth direction. Two sets of VAlN samples were used, one manufactured by HPPMS (high power pulsed magnetron sputtering) and one by dcMS (direct current magnetron sputtering). Micropillars oriented between 0° and 90° to the growth direction were investigated to assess the effect of texture. Moreover, compression tests on micropillars with different oxygen content were performed to separately investigate this influence.
For pillars with increasing oxygen content, a decrease in fracture stress and strain was observed. Furthermore, it was shown that different load rates between 0.1 mN/s and 1.0 mN/s have no influence on fracture stress and strain. Pillars with varying grain orientation show a reduction of fracture stress and strain with increasing angle between the growth and loading directions. In all cases, the specimens produced with HPPMS showed a higher strain and fracture stress than those produced with dcMS. This behavior could be explained by the typical microstructures resulting from the growth process. These experimental results were directly connected to finite element modelling by informing the underlying decohesion law and in turn comparing the computational prediction of the effect of grain orientation on critical stress.