Reliable non-destructive detection and characterization of material degradation caused by high-temperature corrosion

Abstract: Components made from nickel-based superalloys are widely used in gas turbines for aircraft and power plants. In addition to high corrosion resistance, they feature very good creep and fatigue strength at temperatures near 1000 °C. Yet, corrosive attack can significantly reduce the mechanical properties, and thus the expected remaining service life of these components. Therefore, in the case of safety-critical parts, detailed information on the component’s actual condition is crucial. In the present study, a non-destructive electromagnetic testing technique was developed that is capable of reliably detecting early degradation caused by high-temperature corrosion on components made of nickel-based alloys. The testing technique combines the use of temperature-resistant sensors and a variation of the component temperature in a wide range. This allows the determination of the magnetic properties of the component as a function of temperature. It was shown that the measurement signals obtained correlates with the degree of chromium depletion. Thus, a reliable and non-destructive detection of degradation caused by high-temperature corrosion was possible. A special feature of the presented testing technique is that degradation can be detected at an earlier stage compared to conventional methods. In addition, the technique enables the characterization of the microstructure condition directly in the component. The applicability of the testing technique was demonstrated for components with concave surface geometries, like turbine blades.