PURPOSE: To reduce the extent of abrasion between both sliding surface layers as well as to make their seizure or binding hard to occur by having two types of these surface layers, where silicon nitride grains are dispersed in an alloy base consisting of phosphorus, cobalt and nickel at different rates, slidden with each other.

CONSTITUTION: In reference to a combination of sliding surface layers, for example, the combination between a surface layer 13 of a piston ring 11 and a surface layer 15 of a cylinder 14 in an internal combustion engine, there is provided with a first surface layer where silicon nitride grains of 0.5-10μm in mean grain size are dispersed as much as 5-40 volume percentage in an alloy base composed of 2-15wt.% phosphorus, 10-40wt.% cobalt, and the rest of nickel in substance. Also there is provided with a second surface layer where the silicon nitride grains of 0.5-10μm in mean grain size are dispersed as much as 5-30 volume percentage in the alloy base composed of 12-15wt.% phosphorus, 10-40wt.% cobalt, and the rest of nickel in substance. Then, both these surface layers are slidden with each other.