Phase transformation of η and σ phases in an experimental nickel-based superalloy

Long, Fei; Yoo, Yong Shim; Jo, Chang-Yong; Seo, Sun-Kyoung; Jeong, Hi-Won; Song, Young-Gyun; Jin, Tao; Hu, Z. Q.

doi:10.1016/j.jallcom.2008.11.121

Cited by 47 publications

(31 citation statements)

References 19 publications

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“…The co-segregation of B, Cr, Mo and W assisted the formation of M 5 B 3 (CrMoW) 5 B 3 borides, shown in yellow in Figure 3c. Additionally, the lamellar η-Ni 3 Ti, indicated by orange, has previously been pointed out in studies of Ni-Co superalloy and IN738 [35][36][37]. Although the Nb and Al intensity in the microconstituents was not so intense (Figure 3b), the distribution of Nb and Al in the solidification product was consistent with that of Ti.…”

Section: Microstructural Examinationssupporting

confidence: 69%

“…In fact, platelet η and nodular σ phases have been observed in cast Ni-Cr-Co superalloys like IN738 [35][36][37]. The σ phase consists of high Co and Cr concentrations [41], besides, the plate-like σ enriched in Co and Cr nucleates around the grain boundaries of GTD-111 superalloy [42].…”

Section: Discussionmentioning

confidence: 99%

“…Basically, co-segregation of Co, Cr, Mo and W, which was confirmed by EPMA mappings, enhanced the formation of σ (CrCo) phase, as shown by dark blue in the EBSD map. Nodular σ phase has also been reported to nucleate and grow from the interdendritic liquid [37]. The result indicated that the chemical compositions of every phase in the terminal solidification products were quite complex.…”

Section: Microstructural Examinationsmentioning

confidence: 99%

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Liquation Cracking in the Heat-Affected Zone of IN738 Superalloy Weld

Chen

Shiue

et al. 2018

Metals

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Abstract:The main scope of this study investigated the occurrence of liquation cracking in the heat-affected zone (HAZ) of IN738 superalloy weld, IN738 is widely used in gas turbine blades in land-based power plants. Microstructural examinations showed considerable amounts of γ' uniformly precipitated in the γ matrix. Electron probe microanalysis (EPMA) maps showed the γ-γ' colonies were rich in Al and Ti, but lean in other alloy elements. Moreover, the metal carbides (MC), fine borides (M 3 B 2 and M 5 B 3 ), η-Ni 3 Ti, σ (Cr-Co) and lamellar Ni 7 Zr 2 intermetallic compounds could be found at the interdendritic boundaries. The fracture morphologies and the corresponding EPMA maps confirmed that the liquation cracking in the HAZ of the IN738 superalloy weld resulted from the presence of complex microconstituents at the interdendritic boundaries.

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Section: Microstructural Examinationssupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Section: Microstructural Examinationsmentioning

confidence: 99%

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Liquation Cracking in the Heat-Affected Zone of IN738 Superalloy Weld

Chen

Shiue

et al. 2018

Metals

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“…However, the addition of refractory elements (i.e. Re and W) also leads to many problems, such as: (1) severe segregation [4,5]; (2) increasing tendency of grain defects formation [6]; (3) complicated solution heat treatments [7]; (4) increasing tendency of detrimental topologically-closed-packed (TCP) phases formation [8]. To overcome above-mentioned problems, approximately 2-6 wt.% Ru has been added to the newly developed single-crystal superalloys.…”

Section: Introductionmentioning

confidence: 99%

Influence of withdrawal rate on the microstructure of Ni-base single-crystal superalloys containing Re and Ru

Liu

et al. 2011

Journal of Alloys and Compounds

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“…σ 상과 η 상은 대표적인 TCP (Topologically close packed) 상으로, 우선, σ 상은 (Cr, Mo) x (Ni, Co) y (x, y = 1~7)의 조성으로 Tetragonal 구조이며, 기지인 γ 상 내 고용 원소인 Cr, Mo, Co, W에 의해 생성되므로 이러한 원소의 고 용강화 효과를 낮추고, 특히 내부식성을 감소시키는 것으로 보 고되고 있다 [20]. 또한 판상의 형태로 성장하여 결함을 유발시 키므로 고온 강도를 저하시키는 원인이 된다 [21]. (27) …”

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Alloy Design and Properties of Ni based Superalloy LESS 1: I. Alloy Design and Phase Stability at High Temperature

Youn¹,

Kang²,

Choi³

et al. 2013

Journal of the Korea Foundry Society

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The alloys required for fossil power plants are altered from stainless steel that has been used below 600 o C to Ni-based alloys that can operate at 700 o C for Hyper Super Critical (HSC) steam turbine. The IN740 alloy (Special Metals Co. USA) is proposed for improved rupture strength and corrosion resistance at high temperature. However, previous studies with experiments and simulations on stable phases at about 700 o C indicated the formation of the eta phase with the wasting of a gamma prime phase, which is the most important reinforced phase in precipitation hardened Ni alloys, and this resulted in the formation of precipitation free zones to decrease the strength. On the basis of thermodynamic calculation, the new Ni-based superalloy named LESS 1 (Low Eta Sigma Superalloy) was designed in this study to improve the strengthening effect and structure stability by depressing the formation of topologically close packed phases, especially sigma and eta phases at high temperature. A thermal exposure test was carried out to determine the microstructure stability of LESS 1 in comparison with IN740 at 800 o C for 300 hrs. The experimental results show that a needle-shaped eta phase was formed in the grin boundary and it grew to intragrain, and a precipitation free zone was also observed in IN740, but these defects were entirely controlled in LESS 1.

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Phase transformation of η and σ phases in an experimental nickel-based superalloy

Cited by 47 publications

References 19 publications

Liquation Cracking in the Heat-Affected Zone of IN738 Superalloy Weld

Liquation Cracking in the Heat-Affected Zone of IN738 Superalloy Weld

Influence of withdrawal rate on the microstructure of Ni-base single-crystal superalloys containing Re and Ru

Alloy Design and Properties of Ni based Superalloy LESS 1: I. Alloy Design and Phase Stability at High Temperature

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