Synthesis and mechanical properties of quaternary Ti–Cr–Si–N nanocomposite coatings deposited by closed field unbalanced middle frequency magnetron sputtering

[Display omitted] ► Ti–Cr–Si–N coatings were synthesized using a closed field unbalanced middle frequency magnetron sputtering method. ► The microstructure of Ti–Cr–Si–N nanocomposite coatings are consisted of nanocrystalline TiN and amorphous Si3N4 or TiSi2 (nc-TiN/a-Si3N4 or a-TiSi2). ► The Ti–Cr–Si–N coatings showed largely increased hardness value of approximately 36.8GPa at Si contents of 7at.%. ► The average friction coefficient of Ti–Cr–Si–N coatings largely decreased from 0.84 to 0.43 with increasing Si contents to 9at.%. Ti–Cr–Si–N coatings were synthesized onto WC and Si (111) substrates using a closed field unbalanced middle frequency magnetron sputtering method. In this study, comparative studies on microstructure and evaluation of mechanical properties of Ti–Cr–Si–N coatings with various Si contents were conducted. The microstructure of Ti–Cr–Si–N nanocomposite coatings are consisted of nanocrystalline TiN and amorphous Si3N4 or TiSi2 (nc-TiN/a-Si3N4 or a-TiSi2). As the Si contents in the coatings increased, the Ti–Cr–Si–N coatings showed largely increased hardness value of approximately 36.8GPa at Si contents of 7at.%, however, when the Si contents was further increased, the hardness of the coatings decreased. The average friction coefficient of Ti–Cr–Si–N coatings largely decreased from 0.84 to 0.43 with increasing Si contents to 9at.%. This result would be caused by the tribochemical reaction, which often takes place in many ceramics, e.g. Si3N4 reacts with H2O to produce SiO2 or Si(OH)2 tribo-layer as a self-lubricant.