Equiaxed dendritic solidification and grain refiner potency characterised through in situ X-radiography

Murphy, A.G.; Mirihanage, Wajira; Browne, David J.; Mathiesen, Ragnvald H.

doi:10.1016/j.actamat.2015.04.060

Cited by 61 publications

(48 citation statements)

References 27 publications

(41 reference statements)

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“…The last-mentioned grain-size value in this set appears to be in fair agreement with earlier grain-refinement efficiency tests using a Mg-Nd-Zn alloy [5]. Further, it is to be noted that grain-size dependence on cooling rate is more pronounced for the alloy with the low grain-refiner addition level, similar to results reported earlier for alloys based on the AlCu system [6]. Finally, solid-area fraction data from these experiments are presented in Figure 4.…”

Section: Solidification Of a Mg-nd-gd Alloy With Zr Additionsupporting

confidence: 79%

The Use of In Situ X-ray Imaging Methods in the Research and Development of Magnesium-Based Grain-Refined and Nanocomposite Materials

Sillekens

Casari

Mirihanage

et al. 2016

JOM

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Abstract:Metallurgists have an ever-increasing suite of analytical techniques at their disposition. Among these techniques are the in-situ methods, being those approaches that are designed to actually study events that occur in the material during for instance solidification, (thermo)-mechanical working or heat treatment. As such they are a powerful tool in unraveling the mechanisms behind these processes, supplementary to ex-situ methods that rather analyze the materials before and after their processing. In this paper, case studies are presented of how in-situ imaging methods -and more specifically micro-focus X-ray radiography and synchrotron X-ray tomography -are used in the research and development of magnesium-based grain-refined and nanocomposite materials. These results are drawn from the EC collaborative research project ExoMet (www.exomet-project.eu). The first example concerns the solidification of a Mg-Nd-Gd alloy with Zr addition to assess the role of zirconium content and cooling rate in crystal nucleation and growth. The second example concerns the solidification of a Mg-Zn-Al alloy and its SiC-containing nanocomposite material to reveal the influence of particle addition on microstructural development. The third example concerns the (partial) melting-solidification of Elektron21/AlN and Elektron21/Y2O3 nanocomposite materials to study such effects as particle Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporationpushing/engulfment and agglomeration during repeated processing. Such studies for one visualize and by that confirm what is known or assumed. Moreover, they advance science by monitoring and quantifying phenomena as they evolve during processing and by that contribute toward a better understanding of the physics at play.Response to Reviewers: The reviewer's comments on the initial version of the manuscript have been taken into account as follows.1) The manuscript has received thorough proof-reading and editing to improve on grammar.2) The manuscript has been restructured in separate sections on experimental procedures on the one and results and discussion on the other hand as suggested. Upon consultation with the concerned editor, track changes was not used as the heavy swapping of text would have rendered the text virtually illegible.3) The discussion of X-ray methods has been extended by adding an additional paragraph to the introduction (paragraph 2) and by discussing the two used methods into more depth under the experimental procedures (sub-section "methods", including the schematic drawings in Figure 1 and Figure 2). The introduction of magnesium alloys as relevant materials for such studies is covered as well under the experimental procedures (sub-section "materials"). Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation ABSTRACTMetallurgists have an ever-increasing suite of analytical techniques at their disposition. Among these techniques are the in-situ methods, being those approaches that are designed to actually stud...

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Section: Solidification Of a Mg-nd-gd Alloy With Zr Additionsupporting

confidence: 79%

The Use of In Situ X-ray Imaging Methods in the Research and Development of Magnesium-Based Grain-Refined and Nanocomposite Materials

Sillekens

Casari

Mirihanage

et al. 2016

JOM

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“…The sample was aligned in a configuration where the broad surface (X-Y plane) of the sheet-like sample is perpendicular to the gravity (Z || g), by which the melt convection and grain motion were reduced to a large extent. The Bridgman furnace was operated in the so-called near-isothermal mode [12,57], and later in standard directional solidification mode with imposed temperature gradients G along the sample length direction (G || Y). In the near-isothermal mode, the furnace temperature (melt temperature) at the commencement of the experiment is 630 o C;…”

Section: Methodsmentioning

confidence: 99%

Revealing the heterogeneous nucleation behavior of equiaxed grains of inoculated Al alloys during directional solidification

Casari

Mathiesen

et al. 2018

Acta Materialia

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An in-situ study on the directional solidification of an inoculated Al-20 wt%Cu alloy under well-controlled constant cooling rates and temperature gradients has been carried out using a microfocus X-radiography set-up. The influences of temperature gradient and cooling rate on the heterogeneous nucleation rate and growth kinetics of equiaxed grains have been studied quantitatively. It is shown that under the same cooling rate, the nucleation rate of grains decreases with increasing temperature gradient. A high temperature gradient also promotes preferential growth of dendrite arms along the temperature gradient direction, and therefore the formation of elongated grains.However, the temperature gradient effects on nucleation and grain growth decrease with increasing cooling rate. It is revealed that the propagation velocity of the nucleation front in directional solidification castings is approximately equal to the ratio between cooling rate Ṫ and temperature gradient . Based on the experimental observations, a novel numerical grain size prediction model has been proposed, in which the temperature gradient effect on the nucleation kinetics was rigorously treated by introducing two new concepts termed as 'inhibited nucleation zone'(INZ) and 'active nucleation zone'(ANZ). The model has been applied to simulate the present insitu solidification experiments. A good agreement was achieved between the predicted grain number density and the experimental measurements, showing the importance of including the temperature gradient effect on heterogeneous nucleation. Furthermore, the present model also has the capability to predict the temperature gradient necessary for the transition from equiaxed to columnar grain growth.

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“…In-situ X-ray radiography has emerged as a versatile technique in solidification science permitting real-time observations of microstructure spatiotemporal evolution through attenuation and/or phase shift of the X-ray field by the material. Apart from the wellestablished synchrotron-based investigations [25], recent advances in compact microfocus Xray source and high-efficiency detector technologies have allowed in-situ X-ray radiographic solidification experiments to be performed in home laboratories [26][27][28][29]. The home-lab technique provides image contrast exclusively by X-ray absorption, and accordingly its 4 application is limited to systems in which the evolving phases can be distinguished from adequately sharp transitions in the X-ray attenuation across phase domains boundaries.…”

Section: Introductionmentioning

confidence: 99%

α-Mg primary phase formation and dendritic morphology transition in solidification of a Mg-Nd-Gd-Zn-Zr casting alloy

et al. 2016

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Microstructure evolution in the commercial Mg-Nd-Gd-Zn-Zr alloy Elektron 21, solidified under nearly isothermal conditions, has been studied via in-situ X-ray radiography. For cooling rates T ≤ 0.075 K/s, primary equiaxed α-Mg dendrites undergo a morphological transition after nucleation and an initial stage of growth. The growth regime is observed to change abruptly from a 3D to a more pronounced anisotropic sheet-like growth occurring predominantly along 〈112 ̅ 0〉 direction, with a 4-5 times increase in the growth velocity. The experimental results together with thermodynamic calculations and density functional theory simulations give support to relate the morphology transition to the formation of ordered rare earth-zinc dimers in the {0001} basal plane and {101 ̅ 1} pyramidal plane of α-Mg lattice. At the temperature where the morphological transition occurs, it is found that both the solute concentration and zinc diffusivity in α-Mg are high enough for dimer formation to occur 2 within a diffusive layer extending a few micrometres from the solid-liquid interface into α-Mg, and thereby open for increased solute-partitioning at the growth front.

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Equiaxed dendritic solidification and grain refiner potency characterised through in situ X-radiography

Cited by 61 publications

References 27 publications

The Use of In Situ X-ray Imaging Methods in the Research and Development of Magnesium-Based Grain-Refined and Nanocomposite Materials

The Use of In Situ X-ray Imaging Methods in the Research and Development of Magnesium-Based Grain-Refined and Nanocomposite Materials

Revealing the heterogeneous nucleation behavior of equiaxed grains of inoculated Al alloys during directional solidification

α-Mg primary phase formation and dendritic morphology transition in solidification of a Mg-Nd-Gd-Zn-Zr casting alloy

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