Development of Lead-Free Bronze Alloys as Bearing Materials for Sustainable Manufacturing in Nigeria

This study develops lead-free bronze alloy compositions as replacement bearing materials for leaded tin bronzes used in sliding bearings manufactured by the Nigerian engineering industry, addressing both environmental regulations on lead and the need for locally optimised bearing alloy formulations. Leaded bronze bearings are widely used in industrial machinery across Nigeria, but lead content makes recycling and worker exposure management problematic, and international regulatory trends are pushing toward lead-free alternatives. Alloy compositions based on Cu-Sn-Bi and Cu-Sn-Zn-Si systems are designed using thermodynamic software as a guide to phase constitution and castability. Alloys are melted and cast in permanent steel moulds at a university foundry in Zaria, Kaduna State. Microstructures are characterised by optical microscopy, SEM-EDX, and XRD. Mechanical properties including hardness, compressive yield strength, and Charpy impact energy are measured. Tribological performance under boundary lubrication conditions is evaluated on a pin-on-disc tribometer against steel disc counterfaces at applied loads of 20, 40, and 60 N. Results show that a Cu-10Sn-4Bi alloy provides bearing performance (wear rate, friction coefficient) comparable to a reference Cu-10Sn-2Pb alloy while eliminating lead, with hardness and yield strength within 5 percent of the leaded reference composition. Bismuth segregation to grain boundaries is confirmed by EDS mapping. Keywords: lead-free bronze, bearing alloy, tribology, sustainable manufacturing, Nigeria.