PURPOSE:To decrease hardness deterioration as well as to obtain excellent heat and abrasion resistance and characteristics of sliding motion in contact by applying to the trochoid surface of a rotor housing a porous-chromium- molybdenum alloy-plated layer containing a specific weight percentage of molyb denum. CONSTITUTION:In a rotor housing 1, dressing is applied to the rear of a liner 11, which a trochoid surface 2 formed on, and is made of, for example, high- tensile steel plate, and this liner 11 is manufactured as by being buried in an aluminum alloy as internal chill. In this case, a porous-chromium-molybdenum alloy-plated layer 12 containing 0.50-2.00wt% of molybdenum is formed on the inner peripheral surface of the liner 11. With this constitution, high heat and abrasion resistance of the trochoid surface 2 and good characteristics of sliding motion in contact can be obtained, and also its hardness deterioration under high temperature can be decreased. Therefore, it is possible to cope with high power modification of the rotary piston engine.
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