an air starter having such a sleeve microfinish has exceeded 125 000 cycles without failure of the blades eventually a rotor shaft 56 39 of the air starter failed due to metal fatigue however there was a minimum of scoring or pitting on the sleeve surface and a minimum of wear on the vanes the inner surface of the sleeve body 28 39 can be provided with a coating 80 which can be made of hard chromium electro coating such as armoloy having a hardness which measures at least 70 on the rockwell c hardness scale hardness tests also indicate a measurement of from 1020 to 1100 on the vickers diamond pyramid hardness scale this equals 70 to 72 on the rockwell c scale the armoloy material conforms to the existing surface of a body including threads flutes scratches etc with detail down to approximately 8 micro inches r m s additionally armoloy will not affect a growth on the surface of the material more than 0 0002 inches under normal circumstances thereby eliminating the need for undersized design calculations in most applications the coating 80 works its way into the surface of the sleeve material and adheres so positively that it will not chip peel crack or flake when subject to standard astm bend tests over a radius equal to half the thickness of the material to which it is applied roughness the finely spaced surface texture irregularity resulting from the manufacturing process or the cutting action of tools or abrasive grains has in general a greater effect on performance than.