Effects of bias voltage and annealing on the structure and mechanical properties of WC0.75N0.25 thin films

We investigated the effects of both bias voltage and annealing on the structure and mechanical properties of WC0.75N0.25 thin films, deposited on Si (1 0 0) substrates by a direct current reactive magnetron sputtering system, in which the negative substrate bias voltage (Vb) was varied from floating (−1.6 V) to −200 V, and the deposited films were annealed at 800 °C for 2 h. The X-ray photoelectron spectroscopy and selected area electron diffraction analyses, along with the density-functional theory (DFT) calculations on the electronic structure, showed that WC0.75N0.25 films were a single-phase of carbonitrides. After annealing, a significant decrease in hardness for the films was observed, being a result of point-defect annihilation as Vb was in the range of floating to −120 V. However, when Vb was in the range of −160 to −200 V, the hardness increased from ∼37 GPa for the as-deposited film to a maximum of ∼43 GPa for the annealed one. This increase in hardness after annealing might be attributed to age-hardening.