Solidification of Nb-bearing superalloys: Part I. Reaction sequences

Abstract

The solidification reaction sequences of experimental superalloys containing systematic variations in Fe, Nb, Si, and C were studied using differential thermal analysis (DTA) and microstructural characterization techniques. The reaction sequences responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system and commercial superalloys of comparable composition. The solute-rich interdendritic liquid generally exhibited two eutectic-type reactions at the terminal stages of solidification: L → (␥ ϩ NbC) and L → (␥ ϩ Laves). The Nibase alloys with a high C/Nb ratio represented the only exception to this general solidification sequence. This group of alloys terminated solidification with the L → (␥ ϩ NbC) reaction and did not exhibit the ␥/Laves constituent. At similar levels of solute elements (Nb, Si, and C), the Fe-base alloys always formed more of the ␥/Laves eutectic-type constituent than the corresponding Ni-base alloys. Silicon additions also increased the amount of the ␥/Laves constituent that formed in the assolidified microstructure, while C additions promoted formation of ␥/NbC. The influence of Nb was dependent on the C content of the alloy. When the C content was low, Nb additions generally promoted formation of ␥/Laves, while Nb additions to alloys with high C led to formation of the ␥/NbC constituent. The results of this work are combined with quantitative analyses for developing ␥-Nb-C pseudoternary solidification diagrams in a companion article.

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.…”

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

“…[2,8] The results of the quantitative analysis of the chemical composition (SEM/EDS) of precipitates are presented in Table 4. For comparison, this table also includes the chemical composition of the Laves phase in weld overlays examined by Cieslak [8], Floren [18] and DuPont [19]. This analysis showed that the elongated phase was enriched in Mo and Nb, and simultaneously it contained low amounts of such elements as Ni, Cr and Fe that do not segregate to interdendritic areas.…”