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

摘要

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 Si_3N_4 or TiSi_2 (nc-TiN/a-Si_3N_4 or a-TiSi_2). As the Si contents in the coatings increased, the Ti-Cr-Si-N coatings showed largely increased hardness value of approximately 36.8 GPa at Si contents of 7 at.%, 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 _(0.4)3 with increasing Si contents to 9 at.%. This result would be caused by the tribochemical reaction, which often takes place in many ceramics, e.g. Si_3N_4 reacts with H_2O to produce SiO_2 or Si(OH)_2 tribo-layer as a self-lubricant.