Columnar to Equiaxed Transition in Peritectic TiAl Based Alloy Studied by a Power-Down Technique

Lapin, J.; Gabalcová, Zuzana; Hecht, U.; Mooney, Robin P.; McFadden, Shaun

doi:10.4028/www.scientific.net/msf.790-791.193

Cited by 5 publications

(15 citation statements)

References 16 publications

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“…Figure 4. Section image of the CET (at x = 76 mm) given by the primary β-phase microstructure from the sample cooled at 30 °C/min in directional solidification experiments [6] using alloy 455, reproduced from a study by Mooney et al [21]. For the purposes of this article, we are concerned with the microstructural analysis, specifically, the CET position, and numerical modelling results from reference [21] for the sample that contained the CET only.…”

Section: Resultsmentioning

confidence: 99%

“…• A combined Bridgman, power-down experiment was conducted on a gamma TiAl alloy [6] and a CET was observed when the cooling rate in the power-down phase was 30 °C/min.…”

Section: Discussionmentioning

confidence: 99%

“…Lapin et al [6] provide a detailed description of directional solidification experiments carried out in a Bridgman furnace using alloy 455. A brief description of these experiments is provided here.…”

Section: Directional Solidification Experiments Using a Gamma Tial Alloymentioning

confidence: 99%

“…%)-referred to hereafter as alloy 455-is part of this study to investigate Columnar to Equiaxed Transition (CET) in transient directional solidification experiments carried out in a Bridgman furnace where traditional Bridgman solidification was combined with the power down method [6]. CET refers to the growth of columnar dendrites in a casting that are subsequently blocked by the nucleation and growth of equiaxed dendrites.…”

Section: Introductionmentioning

confidence: 99%

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Conditions for CET in a gamma TiAl alloy

Mooney

Lapin

Klimová

et al. 2015

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. The solidification of gamma TiAl alloys is of interest to the aerospace and automotive industries. A gamma TiAl multicomponent alloy: Ti-45.5Al-4.7Nb-0.2C-0.2B (at. %) has been the focus of a study to investigate the solidification conditions that led to a Columnar to Equiaxed Transition (CET) in a directional solidification experiment where traditional Bridgman solidification was combined in series with the power down method. In this paper, a numerical modelling result (a locus plot of columnar growth rate and temperature gradient) from this experiment is superimposed onto CET maps generated using an established analytical model for CET from the literature. A parametric study is carried out over suitable ranges of nucleation undercooling and nuclei density values. The predicted CET positions are compared with the experimentally measured CET position. Reasonable agreement is found at low levels of nuclei density. The paper concludes with estimates for the solidification conditions (nuclei density and nucleation undercooling) that led to the CET.

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Section: Resultsmentioning

confidence: 99%

“…• A combined Bridgman, power-down experiment was conducted on a gamma TiAl alloy [6] and a CET was observed when the cooling rate in the power-down phase was 30 °C/min.…”

Section: Discussionmentioning

confidence: 99%

Section: Directional Solidification Experiments Using a Gamma Tial Alloymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Conditions for CET in a gamma TiAl alloy

Mooney

Lapin

Klimová

et al. 2015

IOP Conf. Ser.: Mater. Sci. Eng.

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“…This characterisation study was a prerequisite for further experiments, which have since been carried out in the same furnace, investigating columnar to equiaxed transition (CET) in a multicomponent alloy of nominal composition; Ti-45.5Al-4.5Nb-0.2C-0.2B (at.%), using a power down method at four different cooling rates; 15 °C/min, 20 °C/min, 30 °C/min and 50 °C/min. Recently, Lapin et al [10] reported on preliminary results from the experiment carried out at a cooling rate of 30 °C/min (CET was observed in the sample processed at 30 °C/min only). The work reported on in this article and the work outlined in references [8], [9] and [10] has been carried out as part of the European Space Agency (ESA) backed research project: GRADECET (GRAvity DEpendance of Columnar to Equiaxed Transition in titanium alloys.)…”

Section: Introductionmentioning

confidence: 99%

Sensitivity analysis of dendritic growth kinetics in a Bridgman furnace front tracking model

Mooney

McFadden

2016

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract.A directional solidification experiment of a Ti-Al-Nb-B-C alloy by power down method is simulated using a Bridgman furnace front tracking model. The effect of varying the dendritic growth parameters; C, the columnar dendrite growth coefficient, and n, the undercooling exponent, is investigated. A matrix of growth coefficients and undercooling exponents -at three levels each, based around a growth law for Ti-46wt.%Al -is applied in simulations, and the effect on columnar dendrite tip temperature, tip velocity, and tip temperature gradient is observed. The simulation results show that the dendrite tip velocity and temperature gradient at the tip are practically unaffected by the use of different growth parameters. However, the predicted columnar dendrite tip undercooling did vary to give the required dendrite tip velocity. This finding has implications for the analysis of microstructural transitions, such as the Columnar to Equiaxed Transition (CET). In conclusion, it is suggested that, for transient solidification conditions, a CET prediction criterion based on tip undercooling is preferable to one that uses growth velocity. IntroductionMany practical analytical models of dendritic growth use the Ivantsov parabolic model [1] to treat diffusion of heat and solute at the dendrite tip. Notable models include; marginal stability theory models based on the work Langer and Müller-Krumbhaar [2], such as the Lipton-Glicksman-Kurz (LGK) [3] model for equiaxed growth at small undercoolings, the Kurz-Giovanola-Trivedi (KGT) [4] model for columnar growth, and microsolvability theory models, as outlined by Kessler and Levine [5], where surface energy anisotropy is accounted for. In any such models, a velocity-undercooling relationship can be determined and it is possible to fit results to a power law curve so that the growth model can be more readily applied in subsequent numerical simulations. Rebow and Browne [6] demonstrated an example of this where the predicted growth velocity, V, was fitted to various levels of dendrite tip undercooling, T, by the power law; V=CT n , where C (the growth coefficient) and n (the undercooling exponent) were the fitted variables for directional solidification of Al-4wt.%Cu and Al-2wt.%Si. In a similar way, the KGT model was used by Rebow et al. [7] to model columnar

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Numerical simulation of Bridgman solidification of binary alloys

Battaglioli

McFadden

Robinson

2017

International Journal of Heat and Mass Transfer

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A transient 2D axisymmetric numerical model for the Bridgman solidification process for a stationary furnace and moving sample is presented. The model is able to predict the evolution of temperature and solid fraction of binary alloys in cases where buoyancy induced convection is negligible, such as in microgravity conditions. A dimensionless form of the governing equations was derived in order to identify the dimensionless parameters that characterize the process, those being the Stefan, Péclet, and Biot numbers. The problem was solved using a finite volume method and an explicit time stepping scheme. To test the efficacy of the model, simulated results were compared with experimental data from the literature and acceptable agreement was obtained. Finally, a parametric analysis was performed for understanding the influence of the process parameters on solidification. One key feature of this study was the inclusion of a term describing the advection of latent heat due to the translation of the mushy zone with varying solid fraction. This thermal transport mechanism was shown to be significant, since its magnitude was comparable to the advection of sensible heat. It was also found that when small Biot numbers were due to low values of the heat transfer coefficients at the surface of the sample, rather than to small sample radii, advective mechanisms were enhanced resulting in more convex shapes of the liquidus isotherm. This highlighted the importance of considering both axial and radial heat fluxes when describing the process.

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Columnar to Equiaxed Transition in Peritectic TiAl Based Alloy Studied by a Power-Down Technique

Cited by 5 publications

References 16 publications

Conditions for CET in a gamma TiAl alloy

Conditions for CET in a gamma TiAl alloy

Sensitivity analysis of dendritic growth kinetics in a Bridgman furnace front tracking model

Numerical simulation of Bridgman solidification of binary alloys

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