Copperbased friction materials containing ZrO2 in different crystal structures were prepared by powder metallurgy(P/M) pressure sintering technology,and the effect of crystal structures of ZrO2 on tribological properties of copperbased P/M friction materials at different braking speeds was investigated under dry conditions.The wear surface morphology and the debris morphology of the samples were respectively observed by optical surface analyzer and scanning electron microscopy,and the effect mechanism of the structures of ZrO2 on the tribological properties of powder metallurgy friction materials was explored.The results show that the friction coefficient and wear rate of the friction material containing monoclinic ZrO2 are higher than those of the friction material containing cubic ZrO2 under the same conditions.With increasing the braking speed,the friction material with cubic ZrO2 suffers relatively smaller decline in the friction coefficient in comparison to the friction material with monoclinic ZrO2,the wear rate of both materials is increased firstly and then decreased.With increasing the braking speed,the wear mechanism of the friction material containing monoclinic ZrO2is changed from adhesive wear and plough wear to delamination wear,while the wear mechanism of the friction material containing cubic ZrO2is transformed from plough wear to oxidation wear and to delamination wear finally.