Thermal Stability and Mechanical Properties of Sputtered Chromium-Molybdenum-Nitride (CrMoN) Coatings

Abstract

Purpose: The purpose of paper is to determinate thermal stability and mechanical properties of sputtered chromium-molybdenum-nitride (CrMoN) coatings. Design/methodology/approach: We have deposited 1.8 m-thick ternary Cr0.5Mo0.5N1.0 films on a CoCrMo alloy using a RF dual magnetron sputtering system, with Cr and Mo targets and N2 as the reactive gas. These films were subjected to various thermal treatments in Ar, air, and microwave plasma. The hardness, Young’s modulus, surface roughness, microstructure, and composition of films were studied by nanoindentation, AFM, x-ray diffraction, and x-ray photoelectron spectroscopy. Findings: The as-prepared CrMoN films consist of an amorphous Cr-rich nitride matrix with Mo-rich nitride crystalline grains, about 15 nm in size. These films are thermally stable up to 600ºC in air. Thermal annealing in the air at 800ºC resulted in an increase in surface roughness and hardness, due to film oxidation, with Cr2O3 as the main crystalline phase. Plasma treatment in a H2/N2 gas mixture, at 800ºC, did not lead to grain growth. Instead, the existing grains were reduced to about 10 nm and a new nanocrystalline phase has been formed. This leads to a decrease in the surface roughness, and an increase in the film hardness. In addition, we have further modified the film properties through a combined thermal treatment process. Thermal annealing in the air at 800ºC, followed by microwave plasma treatment at 800ºC resulted in a film with decreased surface roughness, and improved mechanical properties. Reversing the order of the thermal treatments resulted in a further decrease in surface roughness, but it shows a reduction in the mechanical properties. Research limitations/implications: The present investigation was carried out with only one composition, Cr0.5Mo0.5N1.0, of ternary thin-film system. Originality/value: The combination of thermal and plasma treatments can be used to control the microstructure, surface topography, and mechanical properties of ternary CrMoN films. Such post-deposition treatments can further improve the materials properties for desired application, and to produce new nanocomposite materials with technologically important combination of properties.