A fine gamma '+alpha cellular structure in Fe-37.3 wt pet Ni-3.6 wt pct Al-3.3 wt pct Ti-0.2 wt pct C and its influence on high-temperature tensile properties

Fe-37.3 wt pet Ni-3.6 wt pet Al-3.3 wt pet Ti-0.2 wt pet C alloy, which rev eals an excellent combination of high strength and good elongation endowed by formation of homogeneous;ly dispersed fine gamma' precipitates in the ma trix during aging at 823 K, has been investigated by means of transmission electron and optical microscopies, electron diffractions, and tensile tests . The influence of unique gamma' + alpha cellular products on the mechanica l properties has also been studied. Because of low elastic mismatch between the austenitic gamma matrix and isomorphic gamma' precipitate phases, the homogeneously distributed precipitate particles, which formed at the early stage of aging, were observed to persist even after long-term aging. After very lengthy aging, the fine gamma' phase particles were changed to coarser gamma' lamellae at the grain boundary reaction front, which were alternate ly arranged with fine alpha lamellae that were estimated to have been trans formed from the austenite-stabilizing-solute(Ni, C)depleted gamma lamellae. The fine duplex gamma' + alpha cellular product did not affect deleterious ly the room-temperature tensile properties of the alloy. However, the cellu lar structure was observed to cause the grain boundary embrittlement of the aged alloy at elevated temperatures higher than 681 K.