Optimization of CuMnNiSnSi medium-entropy bronze alloys via solution-aging treatment: Tribological behavior under starved oil lubrication and dry sliding

The (CuMnNiSn)_100-xSi_x (x = 2, 4, and 6 in molar ratio) medium-entropy bronze alloys were subjected to solution-aging treatment to refine the microstructure and reduce compositional segregation. The effects of Si content and the solution-aging treatment on the microstructure and mechanical properties were systematically investigated. The tribological behavior of the treated CuMnNiSn)_100-xSi_x alloys under starved oil lubrication and dry sliding conditions was analyzed. As the Si content increases to 4 at.%, the precipitation of rod-like (Mn,Ni)₃Si intermetallic compound within the face-centered cubic (FCC) matrix gives rise to significant hardening in the alloy. The solution-aging treatment contributes to the alloy's ductility and fracture toughness by enhancing compositional homogeneity while reducing the content of brittle phases. As the Si content increased from 2 to 6 at.%, the wear rate of the treated alloys monotonically decreased from 5.22 × 10⁻⁷ to 1.28 × 10⁻⁷ mm³ N⁻¹ m⁻¹ under starved oil lubrication conditions and from 5.32 × 10⁻⁵ to 1.08 × 10⁻⁵ mm³ N⁻¹ m⁻¹ under dry sliding conditions. The treated (CuMnNiSn)₉₄Si₆ alloy exhibited a threefold improvement in wear resistance compared to the treated (CuMnNiSn)₉₈Si₂ alloy under starved oil lubrication conditions. This improvement further increased fourfold under dry sliding conditions, due to the formation of a locally-protective glaze layer (composed of SnO₂ and SiO₂) on the worn surface.