Solidification of Nb-bearing superalloys: Part II. Pseudoternary solidification surfaces

Abstract

Equilibrium distribution coefficients and pseudoternary solidification surfaces for experimental superalloys containing systematic variations in Fe, Nb, Si, and C were determined using quenching experiments and microstructural characterization techniques. In agreement with previous results, the distribution coefficient, k, for Nb and Si was less than unity, while the ''solvent'' elements (Fe, Ni, and Cr) exhibited little tendency for segregation (k Ϸ 1). The current data were combined with previous results to show that an interactive effect between k Nb and nominal Fe content exists, where the value of k Nb decreases from 0.54 to 0.25 as the Fe content is increased from Ϸ2 wt pct to Ϸ47 wt pct. This behavior is the major factor contributing to formation of relatively high amounts of eutectic-type constituents observed in Fe-rich alloys. Pseudoternary ␥-Nb-C solidification surfaces, modeled after the liquidus projection in the Ni-Nb-C ternary system, were proposed. The Nb compositions, which partially define the diagrams, were verified by comparison of calculated amounts of eutectic-type constituents (via the Scheil equation) and those measured experimentally, and good agreement was found. The corresponding C contents needed to fully define the diagrams were estimated from knowledge of the primary solidification path and k values for Nb and C.

Microsegregation and Precipitates in Inconel 625 Arc Weld Overlay Coatings on Boiler Pipes / Mikrosegregacja I Wydzielenia W Powłokach Ze Stopu Inconel 625 Napawanych Łukowo Na Rury Kotłowe

“…The Laves phase exhibits a hexagonal crystal structure and is characterized by A 2 B stoichiometric composition, where A stands for Ni, Fe and Cr, while B stands for Nb, Mo, Ti and Si. It is worth noting that the results acquired in the present study are consistent with the results presented by DuPont [2,[14][15][16], Silva [17] and Maguire [21]. It was also found that precipitates in the shape of a parallelogram contain much more Ti than the formerly discussed elongated precipitations.…”

“…The distribution of Cr and Fe in the weld overlay was relatively uniform. Similar distribution of elements in an Inconel 625 weld overlay were obtained by Cieslak [11][12][13], DuPont [14][15][16] and Silva [17]. The lighter regions on the Nb and Mo distribution maps (SEM/EDS) correspond to interdendritic regions enriched with Mo and Nb (Fig.…”

Aspectos metalúrgicos de revestimentos dissimilares com a superliga à base de níquel inconel 625

“…O padrão de difração de área selecionada deste precipitado é apresentado na Figura 11b, o qual foi caracterizado inequivocamente como sendo fase Laves. Foram observadas ainda grandes colônias de fases secundárias com morfologia eutética lamelar rica em Nb, bem como longas cadeias de estruturas eutéticas ao longo das regiões interdendríticas e intercelulares, como pode ser observado na De fato, a morfologia destes eutéticos assemelha-se a algumas formações eutéticas observadas nos trabalhos de Dupont et al [38,39] e Cieslak et al [40], a qual foi considerada pelos autores característica de fase Laves rica em Nb. As informações obtidas até então são consistentes com os resultados reportados na literatura.…”

Multiphase solidification in multicomponent alloys

“…Laves phases and Nb-carbides NbC are known to form in eutectic reactions. The systematic study by DuPont et al [141][142][143], spanning from DTAexperiments and microsegregation analysis of fusion welded samples to modeling microsegregation and phase formation along the solidification path of various alloys, highlights the major role played by carbon.…”