Evolution of the microstructure, residual stresses, and mechanical properties of W-Si-N coatings after thermal annealing

W-Si-N films were deposited by reactive sputtering in a Ar + N-2 atmosphere from a W target encrusted with different number of Si pieces and followed by a thermal annealing at increasing temperatures up to 900 degrees C. Three iron-based substrates with different thermal expansion coefficients, in the range of 1.5 x 10(-6) to 18 x 10(-6) K-1 were used. The chemical composition, structure, residual stress, hardness (H), and Young's modulus (E) were evaluated after all the annealing steps. The as-deposited film with low N and Si contents was crystalline whereas the one with higher contents was amorphous. After thermal annealing at 900 degrees C the amorphous film crystallized as body-centered cubic alpha-W. The crystalline as-deposited film presented the same phase even after annealing. There were no significant changes in the properties of both films up to 800 degrees C annealing. However, at 900 degrees C, a strong decrease and increase in the hardness were observed for the crystalline and amorphous films, respectively. It was possible to find a good correlation between the residual stress and the hardness of the films. In several cases, particularly for the amorphous coating, H/E higher than 0.1 was reached, which envisages good tribological behavior. The two methods (curvature and x-ray diffraction) used for calculation of the residual stress of the coatings showed fairly good agreement in the results.