Microstructural evolution in a nickel based superalloy for power plant applications as a consequence of high temperature degradation and rejuvenation heat treatments
conference contributionposted on 12.03.2014, 15:27 authored by Zhiqi Yao, Mark JepsonMark Jepson, Rachel ThomsonRachel Thomson, C.C. Degnan
The microstructural evolution of the Ni-based superalloy CMSX-4 including the change in gamma prime size and distribution and the degree of rafting has been examined in detail using field emission gun scanning electron microscopy (FEGSEM) and transmission electron microscopy (TEM) after high temperature degradation and rejuvenation heat treatments. The relationship between the microstructure, mechanical properties and the applied heat treatment procedures has been investigated. It is shown that there are significant differences in the rafting behaviour, the size of the ‘channels’ between the gamma prime particles, the degree of rafting and the size of the tertiary gamma prime particles in each of the different microstructural conditions studied. Chemical segregation investigations were carried out to establish the cause of reduced mechanical properties of the rejuvenated sample after high temperature degradation compared to an as-received sample after the same degradation procedure. The results indicate that although the microstructure of as-received and rejuvenated samples were similar, the chemical segregation was more pronounced in the rejuvenated samples, suggesting that chemical segregation from partitioning of the elements during rejuvenation was not completely eliminated. The aim of this research is to provide greater understanding of the suitability of rejuvenation heat treatments and their role in the extension of component life in power plant applications.
The authors would like to acknowledge the support of the Technology Strategy Board (Project Number TP/5/MAT/6/I/H0101B) and the following companies: Alstom Power Ltd., E.ON New Build & Technology Limited, Doosan Babcock, National Physical Laboratory and QinetiQ for their valuable contributions to the project.
- Aeronautical, Automotive, Chemical and Materials Engineering