Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography—I: In icosahedral AlPdMn grains

Agliozzo, S.; Brunello, Elisabetta; Klein, Holger; Mancini, Lucia; Härtwig, J.; Baruchel, J.; Gastaldi, J.

doi:10.1016/j.jcrysgro.2005.04.013

Cited by 7 publications

(8 citation statements)

References 28 publications

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“…This "in situ" observation of pore evolution during melting and solidification disclose, for the first time, that the pores encountered in as-grown quasicrystal grains [2][3] [4],with sizes ranging from some micrometres to a few ten micrometres, do not appear during the solidification process. The fact that they were only detected when growing in a band at about two millimetres ahead of the melting interface (Fig.…”

Section: Discussionmentioning

confidence: 96%

“…Since they have been successively observed in thin foil of the Al-Cu-Fe icosahedral phase [1], both at the surface and in the volume of bulk icosahedral Al-Pd-Mn grains [2] [3] and in the volume of quasicrystalline grains of some other alloys and structures [4], pores are generally admitted as important special features of quasicrystals. However as all these previous studies were carried out at room temperature, as well after interrupted [5] [6] as complete [7] [8] growth, it is difficult to decide between the two hypotheses which have been put forward to explain their origin, namely the thermal vacancy condensation [7] and the hierarchical structure [8].…”

Section: Introductionmentioning

confidence: 99%

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In situobservation of pore evolution during melting and solidification of Al–Pd–Mn quasicrystals by synchrotron X-ray radiography

Gastaldi

Schenk

Reinhart

et al. 2006

Philosophical Magazine

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It is now generally admitted that pores are intriguing special features of quasicrystals. Therefore, we have performed an "in situ" and real time observation of the pore evolution during directional solidification and melting cycles of an icosahedral Al-Pd-Mn bi-grained sample, by synchrotron X-ray radiography. Rather surprisingly, no pore was observed to grow during the solidification stages. Nucleation and growth of pores were firstly seen during melting. These pores were subsequently shrinking either just being absorbed or during resumption of directional solidification. It is concluded that the vacancy origin of pores is certainly valid whereas the vacancy supersaturation, needed thereby to explain their growth, would be more probably related to the peculiar structure of quasicrystal than to the destruction of the thermal equilibrium. growth, it is difficult to decide between the two hypotheses which have been put forward to explain their origin, namely the thermal vacancy condensation [7] and the hierarchical structure [8]. Therefore, we have performed an "in situ" and real time observation of the pore evolution during directional solidification-melting cycles of an Al-Pd-Mn bi-grained sample, by synchrotron radiography, in order to grasp, more precisely, the origin of these intriguing species. II Experiments:The synchrotron experiments were carried out at the ID 19 beam line of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). One thin Al-Pd-Mn sample (40x6x0.7 mm 3 ) cut in an ingot prepared at the composition which gives quasicrystal grains soon after the beginning of the solidification process (Al 72.4 Pd 20.5 Mn 7.1 ), was melted and solidified two times inside a graphite crucible held vertically in a two heating-zone furnace. This furnace, described previously in detail [9], is permeable to X-rays and thereby allowed us to follow the course of the solidification/melting of the investigated sample, under a 20K/cm gradient, a pressure of about 3x10 -7 mbar and pulling velocities ranging from 0 to 3.6 µm/s. Radiographs were recorded all along the processes, at the X-ray energy of 24 keV, either by using a CCD camera developed at the ESRF [10]or exposing High Resolution (<1µm) photographic plates (Ilford L4). The camera was fitted with an optics leading to an effective pixel size of 7.46 µm and a large field of view (15x15 mm 2 ). According to the high coherence of the beam delivered by the ESRF synchrotron source, phase contrasts were recorded in addition to absorption contrasts on radiographs, which increased the sensitivity to grain inhomogeneities of the technique. III Results:The sample, as cut in the master ingot (section II), was completely melted before being submitted to two partial solidification/melting cycles. Rather surprisingly, no pore was detected during the solidification stages at the spatial resolution allowed by our technique (≅1µm). The appearance of micrometric pores was firstly observed during melting, at about 2 mm ahead of the regressive interface, whil...

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

In situobservation of pore evolution during melting and solidification of Al–Pd–Mn quasicrystals by synchrotron X-ray radiography

Gastaldi

Schenk

Reinhart

et al. 2006

Philosophical Magazine

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“…The number of different samples of each phase available for this study is not big enough to conduct a systematic study of the influence of the solidification techniques as it has been done on i-Al-Pd-Mn [1]. However, in combination with the results from Part I [1], the present study allows to conclude the absence of correlations between the existence of pores and these techniques.…”

Section: Discussionmentioning

confidence: 95%

“…Pores in the bulk of quasicrystals have firstly been observed in i-Al-Pd-Mn quasicrystal by Mancini and co-workers [1]. These pores are usually facetted and have the shape of a dodecahedron.…”

Section: Introductionmentioning

confidence: 92%

Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography: Part II, in grains of other alloys and structures than AlPdMn

Brunello

Agliozzo

Klein³

et al. 2005

Journal of Crystal Growth

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“…Let us mention, in addition to the detailed study of pores in quasicrystals [10], and their evolution under thermal annealing [11] or melting and solidification [12] which give clues about the origin of the porosity, the investigation of high speed industrial sprays, which provide the experimental data to develop and validate liquid breakup models [13]. Grazing incidence reflectivity phase contrast imaging has also been demonstrated, the difference in optical path between terraces being in this case sufficient to observe monomolecular steps at a solid surface [14].…”

Section: Phase Contrast Imaging 'Holotomography'mentioning

confidence: 99%

Advances in synchrotron hard X-ray based imaging

Baruchel

Bleuet

Bravin

et al. 2007

Comptes Rendus. Physique

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Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography—I: In icosahedral AlPdMn grains

Cited by 7 publications

References 28 publications

In situobservation of pore evolution during melting and solidification of Al–Pd–Mn quasicrystals by synchrotron X-ray radiography

In situobservation of pore evolution during melting and solidification of Al–Pd–Mn quasicrystals by synchrotron X-ray radiography

Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography: Part II, in grains of other alloys and structures than AlPdMn

Advances in synchrotron hard X-ray based imaging

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