R. Nakkalil, N. Richards, M. Chaturvedi
Sep 1, 1992
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Journal
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
Abstract
Abstract This contribution discusses the results of an analytical electron microscopy study of precipitates and insolubles in the NiFe-based superalloy Incology 903. The large insolubles in the alloy are observed to be carbides and/or carbonitrides of niobium and titanium. During thermomechanical processing, fine carbides are observed to precipitate on grain boundaries and prior grain boundaries. Also observed to precipitate along the grain boundaries and prior grain boundaries are MNP-type (M ≡ Nb, Ti; N ≡ Ni, Co, Fe) phosphides, a phase rich in niobium. The relative proportion of carbides to phosphides is observed to increase with an increase in the final solution treatment temperature, with complete phosphide dissolution at 975°C/1 h. The phosphides are observed to have an orthorhombic crystal structure with cell dimensions a = 5.99 A , b = 3.35 A and c = 7.06 A . The chemical composition of the coarse carbides, fine carbides and phosphides has been determined. The chemical composition and lattice parameter indicates the phosphides to be based on NbCoP with iron and nickel substituting for some of the cobalt sites.