Effect of coating architecture on stress and energy relief efficiency of TiZrN coating on Si substrate

Abstract

This study aims to investigate the extent of stress relief achieved by employing different types of coating architectures, and evaluate the energy relief efficiency in the coating architectures by an energy-balance physical model. TiZrN, TiZrN/Ti, TiZrN/TiN and TiZrN/TiN/Ti coatings with various thickness of TiN were deposited by unbalanced magnetron sputtering. Laser curvature method and the average X-ray strain method combined with nanoindentation were used to measure the residual stress of the entire coating and individual layers, respectively. Experimental results showed that higher stress relief in TiZrN coating could be attained by introducing an interlayer with TiN/Ti architecture than by adding a single Ti interlayer. The tri-layer specimen with a 300-nm TiN layer showed the largest stress relief among all specimens, where the TiZrN coating had the lowest residual stress, -2.01 GPa. The energy-balance model postulated that the release of stored elastic energy in the top coating and in the Si substrate were both converted into the plastic work of the Ti interlayer. The model analysis indicated that the TiN transitional layer served as a channel that effectively transferred the stored elastic energy in TiZrN to the Ti interlayer, by which the distinct stress gradient at the original TiZrN/Ti interface could be reduced, thereby increasing the plastic deformation capacity of the underlying Ti interlayer, and therefore a larger fraction of the residual stress in TiZrN was relieved compared to the TiZrN/Ti bilayer coating. Adding a TiN transitional layer into the TiZrN/Ti coating system only slightly changed the overall energy relief efficiency, while it increased the energy relief fraction in the TiZrN coating. The stress relief in an architectured coating, including transitional layer and metal interlayer, should be evaluated based on the measurements of overall stress and the stress in the major hard coating. The energy balance model could be employed to differentiate the fraction of energy relief in hard coating and in Si substrate, by which the efficiency of stress relief, or energy relief, could be correctly revealed.