The evolution of the microstructure during creep of a powder processed polycrystalline nickel base superalloy for turbine discs has been investigated. The objective was to achieve better understanding of the grain-level processes during creep, with particular emphasis on the variation of the intergranular and intragranular secondary and tertiary gamma prime size, distribution and properties, as well as of the grain boundary character. To this end, miniature specimens with different microstructures produced by altering heat treatment were subjected to interrupted creep tests in argon atmosphere. Subsequent post-test examination using high resolution microscopy and microanalysis techniques, as well as examination of the nature of the fracture surfaces, clarified the correlations between microstructure evolution and creep resistances.
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