Patent ID: 7150798

Claim:
A method of determining the service metal temperature of a γ/γ′ MCrAlY-coated component after use of the component in a high temperature environment, where the γ/γ′-MCrAlY-coating of the component exhibits a non-equilibrium γ/γ′-microstructure at a temperature lower than the temperature during operation and the depletion of chromium from the γ/γ′-MCrAlY-coating still allows the α-Cr phase to form, the method comprising: (a) measuring qualitatively impedance curves or measuring the coating electrical conductivity and magnetic permeability of the non-equilibrium MCrAlY-coating of the component in the post-service condition at different locations of the component by means of a multi-frequency eddy current system; (b) then subjecting the coated component to a heat treatment to transform the non-equilibrium MCrAlY coating into an equilibrium microstructure of the coating; (c) then measuring qualitatively impedance curves or measuring the electrical conductivity and magnetic permeability of the equilibrium MCrAlY-coating at different locations of the component by means of a multi-frequency eddy current system; and (d) determining the exposure temperature of the different locations of the component based on the difference in the measured impedance curves or the measured conductivities and permeabilities, before and after the heat treatment according to (b).