Effects of Long-Time Exposure in Alloy 625 at 12OO�F, 1400�F and 1600�F

Radavich, J.F.; Fort, Arthur W.

doi:10.7449/1994/superalloys_1994_635_647

Cited by 39 publications

(16 citation statements)

References 3 publications

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“…Accordingly, almost all of the published ageing studies carried out using Alloy 625 have focused principally on the formation and evolution of these two phases and the subsequent mechanical effects thereof 10 viz. a discussion of the grain behaviour is absent [11,12,13,14,15,16,17,18,19].…”

Section: Introductionmentioning

confidence: 99%

Grain coarsening behaviour of solution annealed Alloy 625 between 600–800 °C

Moore

Taylor

Tracy

et al. 2017

Materials Science and Engineering: A

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As with all alloys, the grain structure of the nickel-base superalloy 625 has a significant impact on its mechanical properties. Predictability of the grain structure evolution in this material is particularly pertinent because it is prone to inter-metallic precipitate formation both during manufacture and long term or high temperature service. To this end, analysis has been performed on the grain structure of Alloy 625 aged isothermally at temperatures between 600-800 • C for times up to 3000 hours. Fits made according to the classical Arrhenius equation describing normal grain growth yield an average value for the activation energy of a somewhat inhomogeneous grain structure above 700 • C of 108.3±6.6 kJ mol −1 and 46.6±12.2 kJ mol −1 below 650 • C. Linear extrapolation between 650-700 • C produces a significantly higher value of 527.7 ± 23.1 kJ mol −1 . This result is ultimately a consequence of a high driving force, solute-impeded grain boundary migration process operating within the alloy.Comparison of the high and low temperature values with the activation energy for volume self-diffusion and grain boundary diffusion identifies the latter as the principle governing mechanism for grain growth in both instances. A decrease in the value of the time exponent (n) at higher temperatures despite a reduction in solute drag is attributable to the Zener pinning imposed by grain boundary M 6 C and M 23 C 6 particles identified from Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDXS) analysis.Vickers hardness results show the dominance of intermetallic intragranular precipitates in 1 the governance of the mechanical properties of the material with grain coarsening being accompanied by a significant increase in hardness. Furthermore, the lack of any correlation with grain growth behaviour indicates these phases have no significant effect on the grain evolution of the material.

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Section: Introductionmentioning

confidence: 99%

Grain coarsening behaviour of solution annealed Alloy 625 between 600–800 °C

Moore

Taylor

Tracy

et al. 2017

Materials Science and Engineering: A

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“…Indeed, while Alloy 625 is a solid solution strengthened alloy in the as-heat treated state thanks to its high chromium and molybdenum contents [1], this alloy was proved in the past to be sensitive to the precipitation of strengthening intermetallic phases such as N i2(Cr,Mo) of P t2Mo structure [5,6,8] or such as the N i3Nb y" phase of DO22 structure due its non-negligible niobium content [3,[5][6][7][8][9][10]. From the open literature, six main phases can be found in the austenitic y matrix after various types o f thermal exposure (y'', 5 and N i2(Cr,Mo) intermetallic phases, M 6C and M 23C6 secondary carbides, MC primary carbides) and over seven minor precipitations (rich a-C r particles, ^ TCP particles, Laves particles, Si-rich particles ...) were identified to nucleate/decompose/transform upon thermal aging [1,3,[5][6][7][8][9][10][11][12][13][14][15][16]. The interested reader is referred to a recent paper from the authors summarizing phases' evolutions in the 550°C-900°C temperature range and analyzing at the impact of the forming process on their precipitation kinetics [17].…”

Section: Introductionmentioning

confidence: 99%

Impact of Thermomechanical Aging on Alloy 625 High Temperature Mechanical Properties

Suave¹,

Soula²,

Bertheau³

et al. 2014

8th International Symposium on Superalloy 718 and Derivatives (2014)

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Alloy 625 is widely used for petrochemical, marine and aerospace applications owing to its outstanding corrosion and mechanical properties at high temperatures. However, this alloy is prone to complex microstructure evolutions above 500°C that may impact its mechanical properties. In this study, the impact of its micro structure evolutions occurring upon long-term thermal aging on its static and cyclic mechanical properties has been studied. Thermal exposures of up to ~ 2000 hours in the 550°C-900°C temperature range have been investigated. TTT diagrams of the 5 and y" phases were established based on high resolution scanning electron microscopy observations. The evolutions of secondary carbides distributions were also followed. It has been observed a steep increase of the room temperature microhardness after overagings performed at 650°C and 700°C due to the precipitation of the y" phase. Moreover, it is also clearly evidenced a strengthening effect of the 5 phase after long-term thermal exposures at temperatures in excess of 700°C. Finally, the impact of a thermal aging in the y" precipitation domain on the high temperature tensile and low cycle fatigue properties was evaluated. It is shown a beneficial effect of the y' ' precipitation to the fatigue life and to the tensile properties up to 750°C. It is also shown that the loss of high temperature ductility is not correlated to the precipitation of grain boundary secondary carbides. y'' precipitation and the y'' ^5 transformation are also shown to be faster under cyclic loading compared to pure thermal aging.

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“…This phase can form directly from the supersaturated solid solution on ageing at relatively high temperatures. Prolonged ageing at relatively low temperatures also causes the precipitates of the metastable y" phase to be replaced by those of the equilibrium 6 phase [6,9].…”

Section: Introductionmentioning

confidence: 99%

“…The microstructure that develops in this alloy after ageing or service for very long periods and the effect of such a microstructure on its mechanical properties have been investigated by a few researchers in the recent years. Radavich and Fort [9] have studied the microstructure of Alloy 625 after ageing in the temperature range of 650 "C to 870°C for up to 46000 h.by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Thomas and Tait [lo] have examined the microstructure and the mechanical properties of the alloy after it had seen long-term service (about 50000 h) at temperatures of around 500" C as the material of construction of feed stock superheaters in a petrochemical plant.…”

Section: Introductionmentioning

confidence: 99%

Influence of Intermetallic Phase Precipitation During Prolonged Service in Alloy 625 on Its Properties

Sundararaman¹,

Mukhopadhyay²,

Banerjee³

2001

Superalloys 718, 625, 706 and Various Derivatives (2001)

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The results of a microstructural investigation on Alloy 625 which has undergone prolonged service at temperatures close to but less than 600" C are reported in this paper. A uniform distribution of precipitates of an intermetallic phase, Ni,(Cr,Mo) with Pt,Mo type structure has been observed in addition to that of the y" phase for service periods exceeding 28,000 h. The Ni,(Cr,Mo) phase has been found to dissolve on ageing at temperatures above 600" C. The dissolution of this phase has been noticed to result in a reduction in hardness and impact properties of the alloy. The occurrence of Ni,(Cr,Mo) phase in this alloy has been discussed by taking the alloy chemistry into consideration. Apart from these intermetallic phases, precipitation of M,C carbide particles within the austenite matrix and the formation of a near continuous film comprising discrete M,C/M,,C, carbide precipitates at grain boundaries have been noticed in the alloy after prolonged service. Energy Dispersive Spectroscopy(EDS) analysis has revealed that the majority of the carbides precipitating at the grain boundaries at temperatures around 600" C are of M,,C, type. The influence of the intennetallic and the carbide phase precipitates on the performance, properties and life of Alloy 625 is also discussed in this paper. Cupcral!o\., :'! S. h2i. 706 arid b'arious l) c r~\ a t i \~: i

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Effects of Long-Time Exposure in Alloy 625 at 12OO�F, 1400�F and 1600�F

Abstract: An investigation was carried out on alloy 625 to study the structural effects

Cited by 39 publications

References 3 publications

Grain coarsening behaviour of solution annealed Alloy 625 between 600–800 °C

Grain coarsening behaviour of solution annealed Alloy 625 between 600–800 °C

Impact of Thermomechanical Aging on Alloy 625 High Temperature Mechanical Properties

Influence of Intermetallic Phase Precipitation During Prolonged Service in Alloy 625 on Its Properties

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