MORPHOLOGICAL CHANGES BEHAVIOR OF FAN-TYPE STRUCTURES OF γ' PRECIPITATES IN NICKEL-BASED POWDER METALLURGY SUPERALLOYS
HU Benfu1), LIU Guoquan1, 2), WU Kai1), HU Penghui1)
1) School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083
2) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083
Cite this article:
HU Benfu LIU Guoquan WU Kai HU Penghui. MORPHOLOGICAL CHANGES BEHAVIOR OF FAN-TYPE STRUCTURES OF γ' PRECIPITATES IN NICKEL-BASED POWDER METALLURGY SUPERALLOYS. Acta Metall Sin, 2012, 48(7): 830-836.
Abstract The variety and complexity of γ' phase morphological changes in heat treatment process of nickel-based powder metallurgy (P/M) superalloy, which contains high volume percentage γ' strengthening phase, is one of hot issues which material researchers focused on. γ' phase morphological changes have important effect on the strength, toughness, high-temperature creep and fatigue property of alloy. Based on the research of heat treameat process in the thirdly nickel-based P/M superalloy (FGH98I), the researcher find that there are γ' fan-structure in solution heat treatment at different cooling rates, and follow-up treatment have obvious influence on γ' fan-structure morphology. Therefore, it is necessary to research scientifically and penetratingly on the formation conditions, formation mechanism, and the effects of different heat treatment process of γ' fan-structure which exist as a kind of special organization morphology. The formation and evolution of fan-type structure in a new type nickel-based P/M superalloy FGH98I was studied by means of FESEM and TEM. The results show that the fan-type structure in alloy FGH98I consists of finger-shaped γ' dendrites and the $\gamma$ matrix between them. It forms only in a selection area characteristic, nucleates inhomogeneously in the chemical segregation area at different scales on highly supersaturated grain boundary and develops by own concentration gradient diffusion. The standard aging makes the fan-type structure growing up and coarsening. The γ' fingers become unstable, transforming into stable cubic shape γ' in low-energy state after high-temperature aging.
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