Channel formation in Pb-Sn, Pb-Sb, and Pb-Sn-Sb alloy ingots and comparison with the system NH4CI-H2O

Sarazin, J. R.; Hellawell, A.

doi:10.1007/bf02645156

Cited by 202 publications

(117 citation statements)

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“…The nucleation and stability of channel segregates were like-wise investigated experimentally and theoretically in a number of studies. [24][25][26] A-segregation is of particular concern to the manufacturers of pressure vessels required for nuclear power generation. Such vessels are created by removing the core of the ingot after casting to create a shell, which is then forged and machined to finish.…”

Section: )mentioning

confidence: 99%

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Pickering

2013

ISIJ Int.

146

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The macro-scale segregation of alloying elements during the casting continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still commonplace, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today's steel ingots are as chemically homogeneous as possible.This article briefly reviews the development of our current understanding of macrosegregation phenomena during the 20 th century, before going on to assess the latest developments in the field of macrosegregation modelling. The aim of the text is to highlight the shortcomings of applying contemporary macromodels to steel-ingot casting, and to suggest practical alternatives. In addition, the experimental characterisation of macrosegregation is explored, and a review of the various techniques currently available is presented.

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Section: )mentioning

confidence: 99%

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Pickering

2013

ISIJ Int.

146

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“…The general mechanism for the formation of the defect has been defined as bouyancy-driven flow in the liquid/solid region of the casting, and the analysis of this mechanism for low temperature systems, including aqueous analogues, has confirmed the fundamental parameters as a balance between the bouyancy driving-force and the resistance offered by the dendrite mesh in the mushy zone. The balance was quantified by Sarazin and Hellawell (4) in terms of the systems Rayleigh Number (Ra); a proposal which was verified by experimental work on a low melting alloy system. Further experimental work by Auburtin et al (5) on a range of segregation-sensitive superalloys confir.med the validity of this approach.…”

Section: Introductionmentioning

confidence: 95%

Freckle Formation in Superalloys

Auburtin¹,

Cockcroft²,

Mitchell³

et al. 2000

Superalloys 2000 (Ninth International Symposium)

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The analysis of the formation mechanisms for freckling and for random gram formation in single crystal castings has resulted in a general understanding of the principles involved, but has not been tested extensively against results in actual superalloy castings. In this work, we present the results of experimental work on the production of freckling in superalloy castings, made directionally in a Bridgemau furnace capable of producing DS castings in which the directional axis can be rotated with respect to gravity.The results indicate that we may account quantitatively for freckle formation through an analysis based on fluid-flow as described by a modified Rayleigh criterion. The theoretical critical condition for freckle initiation is found to be a Rayleigh Number of unity; the experimental determination of this critical value is found to be in the region of 0.7 -0.9 depending on the alloy examined. We ascribe the difference in these values to the secondary features of the dendrite morphology. The relation to random grain nucleation is found to lie in the role of isotherm curvature in the solidifying region. This aspect is examined by the use of ProCAST computations in both castings and remelt ingots. morphology may have a large influence on the numerical value of Ra, and therefore on the development of freckling in a casting. Thirdly, the common industrial solution to freckling in directional castings, that of increasing the solidification temperature gradient, is shown to be reasonable in that its primary influence is on the dendrite spacing, but it is also seen to have clear limitations in the case of large thermal sections as would, for example, exist in large castings. Finally, the role of casting geometry and imperfect isotherm control during solidification is not at present part of the analysis and should be included for a full description of the phenomenon.

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“…%Pb alloys is chose. Sn-Pb alloy system is a typical eutectic system and it has been investigated for a long time [17][18][19]. Furthermore, the thermal dynamic and physical properties are ready to obtain, and they can be found in references [17,[21][22][23].…”

Section: Numerical Model and Simulation Settingsmentioning

confidence: 99%

Simulation of thermos-solutal convection induced macrosegregation in a Sn-10%Pb alloy benchmark during columnar solidification

Zheng

Kharicha

et al. 2016

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

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Abstract:In order to investigate the effect of thermo-solutal convection on the formation of macrosegregation during columnar solidification, simulations with a liquid-columnar two phase model were carried out on a 2D rectangular benchmark of Sn-10%Pb alloy. The solidification direction in the benchmark is unidirectional: (1) downwards from top to bottom or (2) upwards from bottom to top. Thermal expansion coefficient, solutal expansion coefficient and liquid diffusion coefficient of the melt are found to be key factors influencing the final macrosegregation. The segregation range and distribution are also strongly influenced by the benchmark configurations, e.g. the solidifying direction (upwards or downwards) and boundary conditions, et al. The global macrosegregation range increases with the velocity magnitude of the melt during the process of solidification. IntroductionMacrosegregation is the inhomogeneous solute distribution at the scale of a casting and it is very sensitive to thermal-solutal convection [1]. It is important to understand the macrosegregation, and be able to model and control it because macrosegregation is usually detrimental for castings. Macrosegregation is mainly due to a combination of microsegregation and relative motion between liquid phase and solid phase [2][3][4][5]. The relative motion during the solidification is induced by different flow phenomena, for example, equiaxed sedimentation, thermo-solutal convection or feeding flow. In this study it is dedicated to illustrate the delicate mechanism of macrosegregation during solidification with the presence of thermal-solutal convection. This is also an important topic in the annual solidification course in Swiss Federal Institute of Technology of Lausanne (EPFL) [4,6]. There are lots of works carried out on lateral solidification benchmark [7][8][9][10][11] while the investigation on the vertical-directional solidification is not sufficient. In order to investigate the effect of thermo-solutal convection on the formation of macrosegregation during vertical-unidirectional solidification, a series of simulations with a liquid-columnar two phase model were carried out on 2D rectangular benchmark of Sn-10%Pb alloy. The aim of this paper is to explore the effect of thermo-solutal convection on macrosegregation in detail.

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Channel formation in Pb-Sn, Pb-Sb, and Pb-Sn-Sb alloy ingots and comparison with the system NH4CI-H2O

Cited by 202 publications

References 16 publications

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Freckle Formation in Superalloys

Simulation of thermos-solutal convection induced macrosegregation in a Sn-10%Pb alloy benchmark during columnar solidification

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