Investigation of the influence of the vanadium content on the high temperature tribo-mechanical properties of DC magnetron sputtered AlCrVN thin films

Abstract

The forming of high-strength steels or new aluminum alloys leads to a steady increase of the load of tools and coatings. One approach is to positively influence the manufacturing process by using thin solid films with self-lubricating features, provided by oxides at high temperatures with low decohesion energies. For the purpose of this study, AlCrN provides the matrix, while vanadium oxides are used to enhance the frictional and wear properties. However, it is not yet clear which minimum amount of vanadium has to be incorporated in DC magnetron sputtered AlCrN coatings to improve the tribological behavior. Therefore, in this study, AlCrVN coatings are synthesized with an increasing vanadium content by means of reactive DC magnetron sputtering. Additionally, a vanadium-free AlCrN coating is used as reference for the tribo-mechanical investigations. The coatings were synthesized up to a vanadium content of 13.5at.-% and no phase change could be detected by means of x-ray diffraction. Moreover, no hexagonal AlN phase, which reduces the mechanical properties and the oxidation resistance, was formed. In contrast to the vanadium-free coating, the hardness of the coatings containing vanadium is slightly reduced. The coating with the smallest vanadium content shows the highest hardness of all analyzed coatings. A heat treatment at 400°C does not lead to any significant changes with respect to mechanical properties, but at 700°C hardness, modulus of elasticity and critical load decreased for all coatings, indicating a significant change in mechanical properties. The ball-on-disc test at room-temperature, 400°C, and 700°C shows the highest wear coefficient for the coating with the lowest vanadium content, due to the poor adhesion of the coating, although this coating shows the highest H/E-ratio.