Study on the Microstructure Evolution and Oxidation Mechanism of Copper-based Powder Metallurgy Brake Pads under High Temperature Thermal Shock Conditions

Thermal shock cycling tests were conducted on copper-based powder metallurgy brake pads at 900 ℃,and the appearance and microstructural changes of the copper-based powder metallurgy brake pads were studied.The morphology and composition of the surface oxides on the friction block were analyzed, and the oxidation mechanism was elucidated.The main components of copper-based powder metallurgy brakes are copper powder, iron powder, graphite, ferrochrome.The results indicated that after 5 thermal shock cycles, the surface of the powder metallurgy brake pad got oxidized and turned light gray.After 10 cycles, the degree of oxidation increased, and slight cracks appeared.After 5 thermal shock cycles, the surface oxides on the friction block did not fully cover the surface, were mainly a mixture of CuO,Cu₂O,FeCr₂O₄ and Fe₂O₃.After 10 cycles, the surface of the friction block was mostly covered by oxides of CuO and Cu₂O.After thermal shock cycling, the interface between the iron powder particles and the copper matrix became more blurred, and the surface morphology of the graphite became rough.The main reason for the formation of cracks on the surface of the friction block is related to the stress caused by the rapid growth of the oxide film and the difference in thermal expansion coefficients of the components.