The effects of temperature, pressure and dissolved oxygen concentration (DO) in water on the wear of the hydrogenated diamond-like carbon (HDLC) at high temperature and pressurized water

The aim of this study is to clarify the wear mechanism of hydrogenated diamond-like carbon (HDLC) coating in high temperature and pressurized water. A new reciprocating autoclave wear tester was developed to conduct the wear test between DLC coated pins against SUS316 plate in high temperature and pressurized water. The results showed that the wear of HDLC in water was greatly influenced by water temperature from 23 °C to 300 °C and dissolved oxygen concentration (DO) from 0.73 mg O/L to 47.5 mg O/L (mg O/L:milligrams oxygen per liter) in water. On the other hand, water pressure in the chamber did not have significant effect on the wear of HDLC when pressure was increased from 10 MPa to 30 MPa at 300 °C. Based on surface analysis by XPS, AFM nano scratch, Raman spectroscopy, and AES on the top most surface of the wear scar of HDLC, softening and oxidation of top layer of wear scar of HDLC was found to be the mechanisms of high wear of HDLC in high temperature and pressurized water. The transformation of sp3 to sp2 at higher water temperature is believed to be responsible for the reduced hardness of the top most surface of HDLC. Oxidation also provided softening of top layer of HDLC at higher DO in water.