Improvement of structural, morphological and mechanical properties of CrNx sputtered thin films by vacuum annealing process

Abstract

In this study, CrNx thin films were prepared on 304 stainless steel substrate by DC reactive magnetron sputtering technique. Different N2 gas partial pressure from 10 to 30% was employed in the sputtering process while sputtering power, sputtering pressure and total film thickness were kept constant. In order to improve structural, morphological, and mechanical properties, vacuum annealing process was adopted on the CrNx thin films at the temperature of 400 °C. The standard characterization techniques such as X-ray diffraction, scanning electron microscope, atomic force microscope and hardness (load force of HV0.1) were used to reveal the properties of as-deposited and annealing films. The as-deposited films show two-phase crystal structure of Cr2N and CrN depending on N2 gas partial pressure. After the annealing process, the films effectively enhance the crystal structure and found the phases change from Cr2N to CrN for the film deposited at low N2 partial pressure. The surface roughness of the films was between 5 - 20 nm, and as expected the annealing films shows smoother surface than the as-deposited films. Hardness of the CrNx films is in the range of 7 to 10 GPa. The mechanism of improvement in structural and mechanical properties of annealing films is introduced based on strain relaxation.