16 via hpt shaft 50 partially expanded combustion gas transitions from hpt section 38 to lpt section 40 driving lpc section 30 and fan 12 via lpt shaft 44 exhaust flow exits lpt section 40 and turbine engine 10 via exhaust nozzle 24 the thermodynamic efficiency of turbine engine 10 is tied to the overall pressure ratio as defined between the delivery pressure at inlet 22 and the compressed air pressure entering combustor 18 from compressor section 16 in general a higher pressure ratio offers increased efficiency and improved performance including greater specific thrust high pressure ratios also result in increased peak gas path temperatures higher core pressure and greater flow rates increasing thermal and mechanical stress on engine components fig2 is a cross section along line 22 of fig1 of a casing 48 which has a rotor shaft 50 inside vanes 26 are attached to casing 48 and the gas path 52 is shown as the space between vanes 26 coating 60 corresponding to the coating of this invention is on rotor shaft 50 such that the clearance c between coating 60 and vane tips 26 t of vanes 26 has the proper tolerance for operation of the engine e g to serve as a seal to prevent leakage of air thus reducing efficiency while not interfering with relative movement of the vanes and rotor shaft in fig2 and 3 clearance c is expanded for purposes of illustration in practice clearance c may be for example in a range of about 0 025 inches to 0 055 inches when the.