TRIBOCHEMICAL CHARACTERIZATION OF THE WORN SURFACE OF THE TERNARY-SYSTEM CU-NI-ZN

Copper-based ternary alloy Cu-Ni-Zn for sliding contacts is investigated with respect to the composition of surfaces worn in abrasion tests and beat treated in vacuum. Analyses of the worn surface composition, the chemical states and the depth profiles on the surfaces of the ternary alloy are carried out, using Auger electron spectroscopy with an ion-sputtering device, as well as the measurement of sliding characteristics. The results indicate that zinc is enriched owing to segregation and is preferentially oxidized on the slid surfaces. The friction coefficient mu has a minimum when the surface includes cuprous oxide, instead of cupric oxide. In order to estimate the degree of the effect of surface temperature on segregation, a polished alloy surface was heated as a simulation experiment and analysed with respect to the altered layer thickness and composition. The results show that zinc segregates on the surface above 100-degrees-C, and the segregation energy is as high as 31.5 kJ mol-1. The results of the model experiments explain well the preferential segregation of zinc on the relevant worn surface. It is noted that a surface layer as thin as 3 nm is sensitive to and has an effect on the friction coefficient in the lower load region of sliding.