Effect of Two-Stage Cooling on the Microstructure and Tribological Properties of Steel-Copper Bimetals

In this paper, the solid-liquid composite method is used to prepare the steel-copper bimetal sample through two-stage cooling process (forced air cooling and oil cooling). The relationship between the different microstructures and friction properties of the bimetal copper layer is clarified. The results show that: the friction and wear parameters are 250 N, the speed is 1500 r/min (3.86 m/s), the friction coefficient fluctuates in the range of 0.06-0.1, and the lowest point is 0.06 at 700 degrees C. The microstructure of the copper layer was alpha-Cu, delta, Cu3P, and Pb phases, and Pb was free between alpha-Cu dendrites. When the solidification temperature is 900 degrees C, the secondary dendrite of alpha-Cu develops. With the decrease temperature, the growth of primary and secondary dendrites gradually tends to balance at 700 degrees C. During the wear process, Pb forms a self-lubricating film uniformly distributed on the surface of alpha-Cu, and the Cu3P and delta phases are distributed in the wear mark to increase alpha-Cu wear resistance.