Thick CrN/AlN superlattice coatings deposited by hot filament assisted HiPIMS for solid particle erosion and high temperature wear resistance

Abstract

There are needs for the development of advanced ceramic coatings for industrial applications, e.g. die casting dies, forming tools, injection molds, valves in oil and gas field, etc. In many cases, under very severe working environment when high pressure and high velocity solid particle erosion and/or wear at high temperatures are involved, traditional hard coatings with thickness of several micrometers may not be satisfactory. High quality thick ceramic coatings are needed to achieve improved durability and performance. In this study, CrN/AlN thick superlattice coatings with thickness up to 20 μm were deposited on stainless steel and WC-Co substrates by reactive high power impulse magnetron sputtering (HiPIMS) combined with hot filament plasma assistance. The coatings were deposited at different hot filament plasma currents (ID), which correlate to different levels of ion fluxes and thermal energies superimposed on growing coatings. The bilayer thickness of these thick CrN/AlN coatings is in the range of 5.4 to 6.7 nm. The microstructure of the coatings gradually changes from loose cone-shaped columnar grains to extremely dense fine columnar grains with increasing ID. These thick CrN/AlN coatings show excellent adhesion and crack resistance with a maximum micro hardness up to 3800 Hv. The solid particle erosion resistance of the coatings was evaluated using an air jet sand erosion tester. The high temperature wear resistance of the coating was measured using a high temperature pin-on-disc tribometer in the ambient air from 600 °C to 1000 °C. It has shown that the hot filament plasma provides greatly enhanced ion flux bombardment and thermal energies, which are critical for obtaining consistent dense structure and fine grains for thick ceramic coating growth.