Plastic deformation behavior of nanostructured CrN/AlN multilayer coatings deposited by hybrid dcMS/HPPMS

Physical vapor deposition (PVD) is a commonly applied technology for deposition of hard coating systems such as chromium (Cr)-based nitride coatings on tools and components used in tribological applications. In such applications, the tools and components are subjected to complex loading situations, which can lead to elastic-plastic deformation of coating/substrate compounds or hard fracture response followed by crack formation. One approach to increase the durability of such load-bearing compounds is the deposition of nanostructured coatings such as CrN/AlN nanolaminates, which exhibit promising properties in terms of hardness and crack resistance. The understanding of the deformation behavior of such multilayers is, however, a key factor for further coating developments. Implementation of nanoscratch analyses in conjunction with high resolution microscopy techniques is an approach to study the tribological behavior of nanostructured coatings and to gain information about their plastic deformation mechanisms under normal and lateral loads. Nanoscratch analyses of the nanolaminate coating system CrN/AlN deposited on quenched and tempered AISI 420 steel substrate and investigation of the resulting plastic deformation are the subjects of current research. In the present work, a hybrid technology, consisting of direct current and high power pulse magnetron sputtering (dcMS/HPPMS), was used for the coating deposition. The CrN/AlN nanolaminate was deposited with a bilayer period (thickness CrN + AlN) of Ʌ ≈ 13 nm. In order to study the plastic deformation of the coating, nanoscratch analyses were performed applying a Berkovich tip. The deformation of coating system under nanoscratch loads was quantitatively analyzed by means of depth profiling using confocal laser scanning microscopy (CLSM). Furthermore, a comprehensive study of the plastic deformation and crack resistance was performed using scanning electron microscopy (SEM). The SEM analyses were carried out on the surface and cross section fractures of the nanoscratch tracks. Scanning transmission electron microscopy (STEM) was applied to explore the micro-scale cracking phenomena underneath the nanoscratch tracks. High resolution transmission electron microscopy (HRTEM) was furthermore applied to explore the mechanism of plastic deformation of the investigated coatings. Based on the results, the CrN/AlN nanolaminate exhibits a significant resistance against plastic deformation and crack formation. Furthermore, the plastic deformation of the investigated coating is explained by grain rotation and grain boundary sliding.