Nanostructured TaC film deposited by reactive magnetron sputtering: Influence of gas concentration on structural, mechanical, wear and corrosion properties

Abstract

TaC coatings were applied on the surface of the AISI316L stainless steel by reactive magnetron sputtering, and the effects of CH4 concentrations (CCH4=0,5,10,20 and 30) on the structural, mechanical, wear and corrosion behavior were investigated. According to the dominant phase structure, deposited films classified into three categories; namely, metallic (Ta phase), ceramic (TaC phase) and amorphous (amorphous carbon phase). Increasing the CCH4 from 0% to 20%, hardness (H) and elastic modulus (E) of the coatings increased from 6.2 and 115.6 GPa to 27.6 and 274.2 GPa, respectively. Further increase in CCH4 led to decrease H and E to 1.5 and 16.3 GPa, respectively. Based on nanoindentation and pin on disk test results, in ceramic coatings due to high coating to substrate hardness ratio, the resistance of the coating against elastic (H/E) and plastic (H3/E2) deformation are the key factors in the determination of wear behavior. It is to say, the coating deposited at CCH4=20% showing the H/E=0.101 and H3/E2=0.28 had the highest wear resistance, while the coating deposited at CCH4=10% with the H/E=0.068 and H3/E2=0.084 showed the lowest wear resistance. Tafel and electrochemical impedance spectroscopy (EIS) tests were also used to investigate the corrosion behavior of the samples. Results showed that the films deposited at CCH4=5 and 10% display the best protective properties, which was attributed to lower porosity index.