Quasicrystalline and Crystalline Phases in Al65Cu20 (Fe, Cr)15 Alloys

Abstract

Two types of icosahedral quasicrystals are observed in Al65Cu20Fe15−xCrx (0 ≦ x ≦ 15) alloys, the face‐centred AlCuFe‐type icosahedral phase with dissoluted Cr and the primitive AlCuCr‐type icosahedral phase with dissoluted Fe. In the vicinity of Al65Cu20Fe8Cr7 a stable decagonal phase (a = 0.45 nm and c = 1.23 nm) forms competitively with the icosahedral quasicrystals. All these three quasicrystalline phases can be regarded as Hume‐Rothery phases stabilized by the energy band factor. The density is measured to be 4.57, 4.44, and 4.11 g/cm3 for the icosahedral Al65Cu20Fe15, the decagonal Al65Cu20Fe8Cr7, and the icosahedral Al65Cu20Cr15 alloys, respectively. Depending on the composition in the range between Al65Cu20Fe8Cr7, and Al65Cu20Cr15, several crystalline phases are observed during the transformation of the AlCuCr‐type icosahedral phase: the 1/1 –3/2‐type orthorhombic (0) and the 1/0 ‐ 3/2‐type tetragonal (t) approximants of the decagonal phase, a hexagonal (h) phase, as well as a long‐range vacancy ordered τ3‐phase derived from a CsCI‐type structure with a = 0.2923 nm. The structures of all the crystalline phases are closely related to those of the icosahedral (i) and decagonal (d) quasicrystals, which leads to a definite orientation relationship as follows: i5 ∥ d10 ∥ o[100] ∥ t[100] ∥ h[001] ∥ τ3[110].

Formation and microstructure of quasicrystals in suction cast Al‐6 wt.% Mn alloys with additions of nickel and iron elements

“…The coexistence of the two phases is due to the epitaxial nucleation and growth of the decagonal phase on the icosahedral phase. Similar phenomenon were observed in the Al-Cu-Cr and Al-Mn-Ni alloys [6,7]. In addition, the periodic value of the Al 40 Mn 7 Fe 2 decagonal phase is 1.1955 nm, smaller than 1.2349 nm of Al 56 Mn 11 Ni 2 .…”

“…So far it has been widely recognized that the Hume-Rothery stabilization of the valence electrons plays a significant role in formation of the quasicrystal, and that the quasicrystalline phase is easily formed when the composition of alloy has the particular electron to atom ratio [25,26]. The value of electron to atom ratio of the Al 56 Mn 11 Ni 2 and Al 40 Mn 7 Fe 2 decagonal phases is respectively 1.84 and 1.81, respectively [6,23]. Thus, we suppose that the Al 56 Mn 11 Ni 2 and Al 40 Mn 7 Fe 2 and A1 60 Mn 11 Ni 4 , A1 20 Mn 3 Cu 2 and Al 24 Mn 5 Zn are the same kind compounds due to the approximate electron to atom ratio of 1.85 [9,23].…”

“…The decagonal phase grows epitaxially on the icosahedral phase and its grain orientation is decided by icosahedral substrates [5][6][7]. Electron diffraction patterns along the ten-fold rotation axis of the decagonal phase show a high resemblance of those of the icosahedral phase along the five-fold axis, suggesting a strong linkage between these two phases [8].…”

Oxidation kinetics of an AlCuFeCr approximant compound: an ellipsometric study

“…However, because of the high degree of disorder usually observed with this compound, we do not exclude the possible presence of other minority Ophases, particularly the O 2 -phase that is often detected along with the O 1 phase and forms with it a twinned microcrystalline structure (for more details about the crystalline structure and microcrystalline texture, see Refs. [20][21][22][23]). Yet, no evidence for the presence of any other crystalline phase is found by XRD.…”

Role of Fe substitution and quenching rate on the formation of various quasicrystalline and related phases

“…But substitution of Fe by Cr shows that regarding phase formation these two elements behave differently e.g. Liu et al (1992) have shown that Al-Cu-Fe system exhibits the face-centred icosahedral while Al-Cu-Cr system corresponds to the primitive, icosahedral phase.…”