In-situ monitoring of stress evolution in high power impulse magnetron sputtering-deposited Ti-Al-N films: Effect of substrate bias and temperature

Abstract

The origin of residual stress during film deposition is a topic of strong interest in the coating engineering community; it requires appropriate investigation tools to explain the different mechanisms acting on the evolution of stress concerning process conditions and material characteristics. In the present work, we used in-situ curvature stress probing combined with ex-situ techniques such as X-ray diffraction cos2α*sin2ѱ applied to the deposition of model Ti0.42Al0.58N coatings. The films were prepared at room temperature and 300 °C, and four substrate bias strategies were studied, namely two constant values of substrate bias (0 V and −75 V), and two systems with alternating high bias and no bias. At room temperature, the application of bias changed the stress from slightly tensile to compressive, while at 300 °C, the use of high bias increased the compressive intrinsic stress by 3 GPa along with hardness. Linking in-situ and ex-situ stress measurements permitted a direct assessment of thermal stress, which varied considerably with bias. The combined analysis revealed the presence of different contributors to stress generation, particularly at the grain boundaries. The relevance of each contributor to the final stress state was found to depend on the energetic growth conditions. Stress monitoring revealed significant differences between the growth of dense films on the porous ones compared to the opposite sequence, suggesting a straightforward pathway to stress mitigation. This is documented by films produced in the alternating −75/0/−75 V bias sequence that presented comparable mechanical properties as films deposited at a constant high (−75 V) bias, but with substantially lower residual stress.