Effect of Cr addition on microstructure and wear resistance of hypomonotectic Cu–Pb alloy

The effects of Cr content on the microstructure, hardness, and wear resistance of Cu–Pb hypomonotectic alloys were investigated. Optical microscope and differential scanning calorimetry (DSC) analysis reveal that when the Cr content exceeds the solubility limit, primary Cr precipitates from the melt as dendrites that grow anisotropically with the crystallographic orientation of 〈1 0 0〉 as the fastest growing directions. The hardness of the alloys is found to increase with increasing Cr content. The wear resistance of the alloys was measured under dry conditions over a load range of 20–80 N using a pin-on-disc type wear testing machine. The worn surfaces were characterized by scanning electron microscopy and the wear mechanism of the alloys was studied. The results show that the wear resistance increases with increasing Cr content, due to a combined effect of strengthening of the matrix and better self-lubrication ability of the lead film.