Mechanical and microstructural characteristics of Cu–Sn–Zn/ Gr metal matrix composites processed by powder metallurgy for bearing materials

Abstract

In this study, powder metallurgy (PM) was conducted on a single type of bronze bearing material, Cu–Sn–Zn using graphite (Gr) as the solid lubricant. Solid lubricants are required for lubrication in extreme conditions where tribological contact bearing surfaces must still be efficiently separated. Solid lubricants that are commonly used include graphite and molybdenum disulfide. PM allows for the production of products with controlled levels of porosity in their structure, where the interconnected porosity in the sintered structure is used to hold an oil reservoir. A self-lubricating sintered bearing is a metallic component with high porosity (20%–25% by volume), which has been impregnated in lubricant oil. The oil contained in the porosity provides constant lubrication between the bearing and shaft, eliminating the need for an external lubricant. This study aimed to determine the effects of wt% graphite on the mechanical properties of a Cu–Sn–Zn/Gr composite. Results of this study revealed that the hardness, density and yield strength values increased in the wt% graphite 0.5 and 1.0, but the rate of wear and porosity values decreased. Meanwhile, when the wt% was 1.5 or 2.0 the hardness, density and yield strength values decreased, whereas the rate of wear and porosity increased. Thus, the mechanical properties of a Cu–Sn–Zn/Gr alloy occurred at a wt% graphite 1.0, with hardness, rate of wear, density, porosity and compressive strength values of 55 BHN, 1.88 × 10−6 mm3/mm, 6.67 gr/cm3, 23.3% and 538 MPa, respectively.