PURPOSE: To improve the lubricating function at a high temperature by forming a coating layer impregnated with solid lubricating material such as CaWO4, etc., in ZrO2 of the surface of a base material.

CONSTITUTION: The inner seal 2 of a rotary heat storage type heat exchanger for a gas turbine comprises a base material formed of heat-resisting stainless steel, a shoe 11 formed with a coating layer 11a on the slidable contact surface 13 of a core, and a diaphragm formed of heat resistant spring material mounted at the opposite slidable contact surface 13 side. The layer 11a is so formed that powder impregnated with solid lubricating material such as CaWO4, etc., is formed in a thickness of 0.1-2mm on the surface of the shoe 11 by plasma spraying, etc., after ZrO2 is partially stabilized with Y2O3. The layer 11a has high heat resistance and low frictional coefficient due to the impregnation of the lubricating material to become a surface hardened layer having excellent lubricating properties, and no peeling of the layer 11a from its base material occurs.