Effect of Cooling Rate on Microsegregation During Solidification of Superalloy INCONEL 718 Under Slow-Cooled Conditions

Shi, Xiao; Duan, Shengchao; Yang, Wensheng; Guo, Hongjian

doi:10.1007/s11663-018-1169-z

Cited by 42 publications

(15 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Combining these results with the above conclusions indicates that Nb is the most principal segregation element in IN718 alloy during solidification under slow-cooled conditions, which is abundant in the remaining liquid at a late stage of solidification and involved in promoting the generation and growth of NbC carbides and the Laves phase. Furthermore, since the size and proportion of the Laves phase in as-cast IN718 alloy are much larger compared with NbC [7], and because the Laves phase begins to be generated below 1190 °C, consuming large amounts of Mo and Nb in the remaining liquid, the SRs of Mo and Nb are alleviated in the sample quenched at 1170 °C.…”

Section: Resultsmentioning

confidence: 99%

“…Given that the general range of cooling rates for industrial ingots is basically less than 20 °C/min [24], and based on our previous studies, the lower the cooling rate, the stronger the segregation tendency of Nb and Mo during solidification [7]. In this continuous quenching experiment, the cooling rate is set to the minimum cooling rate that can be accurately measured by the experimental equipment, that is, 5 °C/min.…”

Section: Methodsmentioning

confidence: 99%

“…In such process of liquid metal cooling, the actual cooling rate is greater than that of the equilibrium in most cases. The solute redistribution will thus occur significantly due to the high content of additional alloying elements, resulting in the formation of a non-uniform matrix and harmful segregation constituents [5,7]. Consequently, some solidification defects, such as element segregation and brittle intermetallic compounds, randomly form during solidification [8], which leads to considerable difficulties in subsequent processing steps and a significant deterioration in the performance of the final castings.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

et al. 2018

Self Cite

View full text Add to dashboard Cite

The solidification and micro- and macro-segregation behaviors of as-cast INCONEL 718 (IN718) alloy at different temperatures under a slow cooling rate (5 °C/min) were investigated in this study. The results indicate that the solid-liquid interface grows into reticulation of hexagons during solidification. The variation trend of the solid fraction and transition rate of the solid phase with solidification time can be well characterized by the Boltzmann and Gaussian distribution, respectively. The order of segregation degree of negative segregation elements is: Fe > Cr > Al. Nb is the most principal positive segregation element, which is abundant in the long-term unsolidified remaining liquid. At the terminal stage of solidification, the increasing tendencies of the Nb and Mo contents in the liquid and the residual liquid density with decreasing temperature reverse due to the formation of the Laves phase. The freckles are most likely to form in the early stages of solidification, at which the liquid fraction is between 0.3 and 0.2, and the temperature range is about 1320 °C to 1310 °C. The information produced is expected to characterize the solidification and segregation behaviors of IN718 alloy when cooled at a slow rate characteristic of larger ingots typical of those required for industrial gas turbines and aircraft engines.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…The excellent high-temperature strength of nickel-based superalloys is largely attributed to the precipitation of intermetallic phases such as γ 0 -Ni 3 (Al, Ti). [1] Electroslag remelting (ESR) is widely used as refining process for superalloys, where the slags are usually based on a CaF 2 -containing system with addition of other oxides such as CaO, Al 2 O 3 , MgO, TiO 2 , and SiO 2 to optimize the property.…”

Section: Introductionmentioning

confidence: 99%

Effect of SiO₂ and TiO₂ on the Crystal Morphology of CaF₂Al₂O₃CaO‐Based Electroslag Remelting Slag

Guo

Zhang

et al. 2021

steel research int.

Self Cite

View full text Add to dashboard Cite

The effect of SiO 2 and TiO 2 on the crystal morphology of 60%CaF 2 ─20% Al 2 O 3 ─20%CaO-type electroslag remelting (ESR) slags are investigated by thermodynamic simulations, differential scanning calorimetry, X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectroscopy. The results suggest that the addition of TiO 2 and SiO 2 changes the type, amount, and sequence of crystal precipitation. CaF 2 is confirmed to be the main crystalline phase in the slag, the morphology of which depends on the slag composition and cooling rate: As SiO 2 content increases, the crystal morphology of CaF 2 in the slag changes from dendrites with smooth surface and relatively large secondary dendrite arm spacing to dendrites with sharp tips and relatively small secondary and tertiary dendritic arm spacings. A classical crystallographic model, Jackson α factor, is proved to correctly predict the crystal morphology as observed in the experiments. It is inferred that the addition of 5 wt% TiO 2 and 4 wt% SiO 2 and a proper cooling rate are favorable to improve the lubrication property of 60% CaF 2 ─20%Al 2 O 3 ─20%CaO-type ESR slags.

show abstract

“…Precipitation of Laves requires a local concentration of Nb (10 -12%) (Biswas et al, 2004), thus occurs most often in the interdendritic regions (Antonsson & Fredriksson, 2005;Biswas et al, 2004;Knorovsky et al, 1989;Manikandan et al, 2014;CH Radhakrishna & Prasad Rao, 1997;Sohrabi et al, 2018;. Laves are an inevitable part of the solidification (Janaki Ram et al, 2004) although it has been reported that increased cooling rates (Antonsson & Fredriksson, 2005;Manikandan et al, 2014;Shi et al, 2018;Y. C. Zhang et al, 2013) and increased Ni and reduced Fe (Lingenfelter, 1989) can reduce their occurrence and continuity.…”

Section: Lavesmentioning

confidence: 99%

Powder Characterisation, Microstructure, and Mechanical Property Evolution of IN625 and IN718 During Selective Laser Melting and Heat Treatment

Pleass¹

View full text Add to dashboard Cite

Additive layer manufacturing is a blanket term for a wide range of processes operating on the same underlying principle. 3D geometry is created by depositing material, layer by layer to create a final 3D geometry. Selective laser melting (SLM) is a branch of additive layer manufacturing, using a laser to fuse a powder bed of metal into each layer. This thesis investigates the SLM process and its application to nickel based superalloy materials, IN625 and IN718. IN625 and IN718 are similar nickel-based superalloys developed for use in aerospace gas turbine engines. In their conventionally manufactured form, these materials have excellent high temperature mechanical properties which make them idea for use in the hot section of gas turbine engines. The aim of this thesis was to investigate how these materials interact with the SLM process and how the material produced can be optimised to improve the range of applications it can be used for. A gap in knowledge regarding a detailed understanding of how the powders morphological and rheological properties influence its ability to be processed by SLM was identified and investigated. A wide range of characterisation methods were implemented with certain important properties being identified to assess a powders processability, namely the particle size distribution and how a significant content of fine particles below 10 μm in size can be detrimental to processability. There is also a lack of a standard powder characterisation methodology specifically for SLM applications. This is addressed with certain methods and measurements being suggested as most promising for wider SLM application. Avalanche flow testing is found to be most applicable to the critical recoating process in SLM and most able to differentiate suitable and unsuitable SLM powders. Following characterisation of the raw material feedstock powder, this thesis also investigates the influence of processing parameters on the microstructure of the material produced by the SLM process. Significant microstructural changes were observed as a result of process parameter changes. This was identified to potentially enable for in-situ modification of material microstructure to suit a manufactured material to its end application. Of the process parameters investigated, laser scan speed was most interesting, suggesting that a faster laser scan speed was able to create a similar microstructure to a much slower one. This was attributed to the reheating effect of the laser beam returning quickly to the adjacent scan line. The validity of this explanation was investigated using a simple, computational thermal model. The result is a new understanding of laser scan speed SLM and its nonlinear relationship with material temperature and microstructure evolution. Finally, post process heat treatments of SLM manufactured IN718 material were investigated. This investigation was in response to a gap in current knowledge regarding heat treatments designed specifically for SLM material. SLM IN718 has been found to have reduced high temperature mechanical properties, specifically stress rupture, which limits its application in demanding environments. In this thesis a range of post process homogenisation heat treatments were investigated, with treatments between 1030 °C and 1060 °C being found to produce material with characteristics consistent with material with excellent stress rupture properties. This novel heat treatment route could provide a method for SLM IM718, and the increased design and geometric freedoms, to be applied in more demanding applications. An evolution of the grain structure in the material was also observed and measured during high temperature homogenisation treatments. This was investigated in the final chapter, and a novel mechanism is suggested for the process of grain coarsening observed. Previously published literature explains similar evolutions as recrystallisation however this did not fit the observations during this thesis. The evolution of grain structure was observed using a process of quasi in-situ electron back scatter diffraction, and a mechanism of grain boundary length reduction, followed by grain growth, is suggested to better fit the observations. It was determined that grains are preferentially selected for growth based on their proximity to a ‘path of least resistance’ of lower angle grain boundaries. The results of this work should benefit industrial users of SLM in the fabrication of Nickel-Based Superalloy material for aerospace applications. The conclusions on powder characterisation offer an insight into available methods to better control and characterise powder feedstock materials for consistent production. Aerospace users especially may find the work regarding post process heat treatments designed specifically for SLM material, to recover lost stress rupture performance, useful in enabling the use of SLM materials, and the design freedom that brings with it, in mor demanding environments than are currently possible.

show abstract

Effect of Cooling Rate on Microsegregation During Solidification of Superalloy INCONEL 718 Under Slow-Cooled Conditions

Cited by 42 publications

References 27 publications

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

Effect of SiO₂ and TiO₂ on the Crystal Morphology of CaF₂Al₂O₃CaO‐Based Electroslag Remelting Slag

Powder Characterisation, Microstructure, and Mechanical Property Evolution of IN625 and IN718 During Selective Laser Melting and Heat Treatment

Contact Info

Product

Resources

About

Effect of Cooling Rate on Microsegregation During Solidification of Superalloy INCONEL 718 Under Slow-Cooled Conditions

Cited by 42 publications

References 27 publications

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

Solidification and Segregation Behaviors of Superalloy IN718 at a Slow Cooling Rate

Effect of SiO2 and TiO2 on the Crystal Morphology of CaF2Al2O3CaO‐Based Electroslag Remelting Slag

Powder Characterisation, Microstructure, and Mechanical Property Evolution of IN625 and IN718 During Selective Laser Melting and Heat Treatment

Contact Info

Product

Resources

About

Effect of SiO₂ and TiO₂ on the Crystal Morphology of CaF₂Al₂O₃CaO‐Based Electroslag Remelting Slag