Comparison of Amorphous and Quasicrystalline Films of SputteredAl0.72Mn0.22

Abstract

X-ray data were collected on films of Alo.72Mno.22Sio.06 sputtered on NaCl at 45, 150, and 230 °C. The 45°C films show a typical metallic-glass structure factor, 5(g), while at 230°C the structure is quasicrystalline plus Al. A combined particle-size and phason strain broadening was applied to the normalized and reduced S(Q) for the 230°C film to bring it essentially into coincidence with the amorphous (45 °C) S(Q) leading us to conclude that the glass, or amorphous, phase represents a defect limit of the quasicrystal. PACS numbers: 61.50.Em, 61.40.+b, 61.55.Hg Conventional microcrystalline models have for some time been considered unsuccessful descriptions of the glassy state of simple metals and alloys. l The discovery of the icosahedral quasicrystal, 2 however, has revived interest in the structure of metallic glasses. As discussed by Widom 3 in his review of icosahedral phases, there is an intimate connection between the local order in glasses, icosahedral quasicrystals, and the crystalline Frank-Kasper phases. 4 The competition among them may be understood if we consider the ways in which frustration, induced by an attempt to close-pack tetrahedra, is relieved or realized. Frank 5 was the first to point out that liquids can naturally accommodate this frustration by forming icosahedral clusters that are clearly not little pieces of, say, an fee crystal. Sachdev and Nelson 6 have more recently developed the statistical mechanics of icosahedral order in dense liquids just above the glass transition and have calculated a structure factor, S(Q), which agrees rather well with the data on amorphous Fe. 7 For U-Pd-Si alloys, Kofalt et a/. 8 have shown with x-ray scattering a similarity in the pair correlation functions, G(r), for a quenched glass and a quasicrystal. Mayer et al 9 have also done an electron-diffraction study to determine the G(r) for an amorphous alloy of Alo.84Vo.i6, produced by electron irradiation of the quasicrystalline phase of the same alloy. In this work they demonstrate the similarity in structure between the "amorphized" quasicrystal and a conventional metallic glass. Urban Moser, and Kronmiiller 10 had previously obtained a very fine grain size for the quasicrystalline phase by annealing the amorphous phase produced by irradiation and had termed the microstructure "microquasicrystalline." Bendersky and Ridder, 11 however, produced increasingly fine droplets-and hence cooling rates-from atomized Alo.86Mn 014 alloys whose apparently amorphous structures, formed smoothly in the limit of high cooling rate, were not considered to be truly amorphous, as in a metallic glass, but rather "microquasicrystalline." Urban et al. n have reviewed this situation-glass versus microquasicrystal-and suggest that (a) the term "microquasicrystalline" may profitably be used only for the quasicrystal whose fine grain size, due to copious nucleation, cannot easily grow, and that (b) the competing amorphous phase, produced by irradiation, is indistinguishable from a conventional metallic glass. This resolution, ...

Atomic decoration of a random-cluster model for icosahedral-phase AlMnSi

“…In the "amorphous" diffraction pattern of AlMnSi of the same composition there is a prepeak at this position. 16 Such a prepeak is usually associated with correlations in the minority atomic species 17 and in this case has been identified with the Mn-Mn distance of -4.5 A. 16 The partial intensities shown here demonstrate that this remains the case in the quasicrystal which is of particular interest because the broadened quasicrystal pattern agrees so well with the amorphous pattern.…”

Multistage Devitrification Behavior of Mg65Cu25Tb10 Bulk Metallic Glass

“…In fact, the fcc TbMg 3 phase (a = 7.324) [15] shows a strong (111) peak at 2.43 Å -1 and a good match of several other peaks, as shown in Figure 3. Interestingly, the previous work of Robertson et al [16] on Al 72 Mn 22 Si 6 found a similar situation, where the appearance of fcc Al phase facilitated the growth of a quasi-crystalline i phase. Because the Mg-Cu-Tb and Al-Mn-Si alloys belong to two different systems, this similarity may suggest that the fcc phases have coherent interfaces (the (111) faces) with the i phase, and the two types of grains are intimately mixed to reduce the strains created by the nonperiodic i phase.…”

“…The PDFs at higher temperatures match well with that of the TbMg 6 , especially within the 1-nm range. This illustrated the existence of icosahedral order in the as-cast state, as suggested by Robertson et al [16] for the Al-Mn-Si system. The PDF at 470 K shows that in stage I, little change can be observed for the first four shells; yet, the intensity of peaks above 10 Å increases, and additional peaks appear around 20 Å (not shown), suggesting that the clusters start to concatenate and correlate.…”

Study on crystallization of nanocrystalline/amorphous Al-based alloy

“…1), which is considered as indication of the existence of short-range order (SRO) in the sample. Previous work showed that the pre-peak corresponding to chemical short-range order (CSRO) of clusters [21][22][23][24][25][26][27][28], which was observed in XRD patterns of most Al-based amorphous alloy, was ascribed to the strong effect among different atoms in alloys and helpful to the formation and stability of amorphous Al-based alloys. In Al-Fe-X alloy, the pre-peaks in XRD patterns correspond to Al-Fe clusters with strong CSRO.…”