Application of spherical indentation and the materials knowledge system framework to establishing microstructure-yield strength linkages from carbon steel scoops excised from high-temperature exposed components

Abstract Industrial power generation turbines operate at elevated temperatures for prolonged periods of time (around 100,000 h) which leads to significant microstructure evolution and mechanical property changes. Due to physical and structural constraints of operational turbines, only small scoop samples can be excised from heat-exposed steel components. Scoop samples at various service time intervals provide valuable information on microstructure changes, for example on graphite formation in carbon steels, with increasing service time. However, mechanical evaluation of such small material volumes poses significant challenges using conventional tests. A novel spherical microindentation technique is applied to evaluate a library of scoop samples ranging between 0 and 99,000 h of service. Furthermore, microstructure and yield strength data for the different exposure periods is used to construct a structure-property (S-P) linkage using the MKS homogenization approach that employs spatial correlations, principal component analysis, and regression techniques. The accuracy of the extracted S-P linkage was assessed on new samples that were not included in the calibration set.