Structural stability of nickel superalloy IN740H after ageing in 750°C

Purpose: Constant demand for electric energy as well as legal and ecological conditions of the country motivate the construction of advanced ultra-supercritical AUSC power units. Increase of the steam parameters to about 700°C and pressure to over 30 MPa requires the application of modern nickel superalloys, which need to be characterized by structural stability at high temperature. The paper presents the results of analysis of structural changes of IN740H superalloy after ageing at 750°C. Design/methodology/approach: Alloy specimens were aged at 750°C for 100 h, 500 h and 1000 h. Evaluation of structure was carried out with the use of light, scanning and scanning-transmission microscopy techniques as well as microanalysis of chemical composition with the use of X-ray spectrometer with energy dispersion (EDS). Findings: The microstructure analyses applying light and electron microscopy revealed the precipitation processes occurring in the structure of IN740H alloy. It has been shown the changes of morphology of γ’ phases and carbides due to heat treatment. Practical implications: The research carried out enabled to know the structural changes of IN740H during ageing at high temperature, which are determined the mechanical and physicochemical properties of alloy. Originality/value: Applied quantity and quality methodology of testing and achieved results of tests broaden the state of knowledge which refers to superalloys of nickel which are recommended to be applied in construction of super-ultra-supercritical boilers (AUSC).