Lawrence Kwok-Yan Li

Tribological and electrochemical properties of Cr–Si–C–N coatings in artificial seawater

Cr–Si–C–N coatings were deposited on Si(100) wafer and stainless steel 316L by using unbalanced magnetron sputtering via adjusting trimethylsilane (Si(CH3)3H, or TMS) flow, and their microstructure and hardness were analyzed by using EDS, SEM, XRD, XPS and nano-indenter. The electrochemical behavior of coatings in seawater were measured by using a CHI660D electrochemical workstation, and the tribological properties of coatings sliding against SiC balls in artificial seawater were investigated by using ball-on-disk tribometers. The results indicated that there were nanocrystallites of Cr(C, N) crystal and amorphous phases such as a-Si3N4 and a-C(a-CNx) in the CrSiCN coatings. With an increase in the TMS flow, the hardness of CrSiCN coatings first increased to the maximum value of 21.3 GPa, and then decreased to 13 GPa. As compared with the CrCN coating, the CrSiCN coatings exhibited a lower friction coefficient. The pitting corrosion only appeared on the wear tracks, and therefore the mechanical wear and wear-accelerated corrosion were the main material deterioration mechanisms in seawater. The impedance modulus and phase value became high in the low frequency range with an increase in the TMS flows. Because the amorphous phase of silicide dispersed in the grains could effectively improve the density of the coatings, thus the coatings deposited at higher TMS flows exhibited better corrosion resistance.

Influence of CrB2 target current on the microstructure, mechanical and tribological properties of Cr–B–C–N coatings in water

Cr–B–C–N coatings with different boron contents (24.6–27.2 at%) were deposited on Si(100) wafers and 316L stainless steels by using closed-field unbalanced magnetron sputtering via adjusting the CrB2 target current. The microstructures, mechanical and tribological properties of Cr–B–C–N coatings in water were characterized by using XRD, XPS, SEM, nano-indentation and ball-on-disk tribometers. The results showed that the soft amorphous BN phases were formed when boron elements were introduced into CrCN coatings. With an increase in the CrB2 target current, the B content increased from 24.9 to 27.2 at%, which caused the a-BN content in CrBCN coatings to increase gradually, and then the hardness of CrBCN coatings decreased from 18.6 ± 0.86 GPa to 16.3 ± 0.28 GPa. Due to the formation of H3BO3, the friction coefficient and wear rates of CrBCN/SiC tribopairs were lower than those of CrCN/SiC tribopairs. When the CrBCN coatings (25.1 at% B) were deposited at the CrB2 target current of 3 A, the lowest values of friction coefficient (0.16) and wear rate (2.1 × 10−7 mm3 N−1 m−1) were obtained simultaneously.

An analysis of the effect of slide-to-roll ratio and surface velocity on wear using energy pulse and mean surface temperature approaches

Abstract The wear behaviour of a dry contact under different slide-to-roll ratios is studied experimentally and the results are analysed by using the energy pulse approach and the mean surface temperature approach. It is found that the energy pulse correlates with mild oxidative wear under dry conditions. Furthermore, there is a critical value of energy pulse where a marked transition from mild oxidative to severe wear occurs. The energy pulse can be used as a simple global parameter to relate mild wear under unlubricated conditions to real operating conditions, and as an aid in the experimental design under sliding–rolling motions. Wear also increases with the calculated mean surface temperature but the correlation between the two is less obvious.