Abstract
Tailoring a material’s properties for low friction and little wear in a strategic fashion is a long-standing goal of materials tribology. Plastic deformation plays a major role when metals are employed in a sliding contact; therefore, the effects of stacking fault energy and mode of dislocation glide need to be elucidated. Here, we investigated how a decrease in the stacking fault energy affects friction, wear, and the ensuing sub-surface microstructure evolution. Brass samples with increasing zinc concentrations of 5, 15, and 36 wt% were tested in non-lubricated sphere-on-plate contacts with a reciprocating linear tribometer against Si3N4 spheres. Increasing the sliding distance from 0.5 (single trace) to 5,000 reciprocating cycles covered different stages in the lifetime of a sliding contact. Comparing the results among the three alloys revealed a profound effect of the zinc concentration on the tribological behavior. CuZn15 and CuZn36 showed similar friction and wear results, whereas CuZn5 had a roughly 60% higher friction coefficient (COF) than the other two alloys. CuZn15 and CuZn36 had a much smaller wear rate than CuZn5. Wavy dislocation motion in CuZn5 and CuZn15 allowed for dislocation self-organization into a horizontal line about 150 nm beneath the contact after a single trace of the sphere. This feature was absent in CuZn36 where owing to planar dislocation slip band-like features under a 45° angle to the surface were identified. These results hold the promise to help guide the future development of alloys tailored for specific tribological applications.
Highlights
The interaction of two contacting solid surfaces is associated, in most cases, with an undesirable dissipation of energy
The tribological performance and sub-surface microstructure evolution of three -brass alloys (Cu with 5, 15, and 36 wt% Zn) were systematically investigated in order to reveal a possible influence of the stacking fault energy
Wear, surface chemistry, material transfer, and the formation of tribologically induced microstructural changes were characterized in nonlubricated reciprocating sliding contacts against Si3N4 spheres for an increasing number of sliding cycles
Summary
The interaction of two contacting solid surfaces is associated, in most cases, with an undesirable dissipation of energy. One-third of the world’s energy resources is dissipated due to such friction processes [1]. One aim of tribology research is to reduce friction and wear and to increase energy efficiency as well as extend the lifespan of tribologically loaded parts to counteract dwindling energy resources. Copper alloys (especially brass and bronze) are favored in many engineering fields owing to their mechanical and chemical properties. Regulatory directives banning the use of heavy metals—including lead—in bearing shells and bushes [5, 6] have drawn additional attention to the research and development of lead-free brass alloys for tribological applications [7, 8]
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