Formation of a quasicrystalline phase in Al–Mn base alloys cast at intermediate cooling rates

Al-rich 94Al–6Mn and 94Al–4Mn–2Fe alloys were suction-cast to evaluate thefeasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediatecooling rates alloyed with non-toxic, easily accessible and affordable additions.The influence of different cooling rates on the potential formation of a quasicrystallinephase was examined by means of scanning and transmissionelectron microscopy, X-ray diffraction and differential scanning calorimetry.Increased cooling rates in the thinnest castings entailed a change in samplephase composition. The highest cooling rates turned out to be insufficient toform an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead,an orthorhombic approximant phase occurred (L-phase). The addition of Fe tothe 94Al–6Mn binary alloy enhanced the formation of a quasicrystalline phase.At intermediate cooling rates of 102–103 K/s, various metastable phases wereformed, including decagonal and icosahedral quasicrystals and their approximants.Rods (1 mm in diameter) composed of I-phase particles embedded in Almatrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al–6Mn

On the constitution of the high-Al region of the Al-Cr alloy system

The compositional range of the Al-Cr alloy system above 75 at.% Al was investigated by powder X-ray diffractometry, differential thermal analysis, scanning and transmission electron microscopy. A hexagonal phase isostructural to mu-Al4Mn (a approximate to 2.00 nm, c approximate to 2.47 nm) was found to be formed in a compositional range from about 78.7 to 81.3 at.% Al. A higher-AlAl11Cr2 phase was associated with the C-centered monoclinic (pseudo-orthorhombic) structure with a approximate to 1.76 nm, b approximate to 3.05 nm, c approximate to 1.76 nm and beta approximate to 90 degrees reported earlier. No orthorhombic structure with a approximate to 3.46 nm, b approximate to 2.00 nm, c approximate to 1.24 nm related in the literature to either Al45Cr7, Al11Cr2 or Al4Cr was revealed at all. The peritectic temperature of the Al11Cr2 phase formation was found to be similar to 865 degrees C and the stability of this phase was confirmed down to 600 degrees C. (c) 2007 Elsevier B.V. All rights reserved

Al-rich region of Al-Pd-Ru at 1000 to 1100°C

Partial isothermal sections of the Al-Pd-Ru phase diagram at 1000, 1050 and 1100 degrees C are presented here. The Al-Pd orthorhombic epsilon-phases dissolve up to similar to 15.5 at.% Ru, Al13Ru4 < 2.5 at.% Pd and Al2Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (Pm (3) over bar, a = 0.7757 nm) C-1 (lm (3) over bar, a = 1.5532 nm) and C-2 (Fm (3) over bar, a = 1.5566 nm) were revealed. An additional complex cubic structure with a approximate to 3.96 nm was found to be formed at compositions close to those of the icosahedral phase. (C) 2007 Elsevier B.V. All rights reserved

An investigation of the high-Al part of the Al-Pd-Ru phase diagram at 790 to 900°C

Partial isothermal sections of the Al-Pd-Ru phase diagram at 790 and 900 degrees C are presented. Complex orthorhombic 8-phases extending from Al3Pd up to 15 at.% Ru exhibit structural variants including transient irregular structures. The Al3Pd2 phase dissolves up to 2 at.% Ru, Al13Ru4 <2.5 at.% Pd and Al2Ru up to 1 at.% Pd. A stable icosahedral quasicrystalline phase is formed around the Al71.5Pd17Ru12.5 composition. At nearby compositions two complex primitive cubic phases with a approximate to 2.0 and approximate to 4.0 nm were observed. These cubic phases exhibit powder X-ray diffraction (XRD) patterns very similar to that of the icosahedral phase. At compositions close to the high-Ru limit of the epsilon-range the electron diffraction patterns of complex orthorhombic structures and ID quasicrystalline structure were revealed. At lower-Al concentrations three ternary cubic phases structurally related to quasicrystals are formed: primitive C (a approximate to 0.75 nm), bcc C-1 and fcc C-2 with a double lattice parameter. (C) 2008 Elsevier B.V. All rights reserved

An investigation of the Al-Pd-Ir phase diagram between 50 and 100 at.% Al

Partial 1100, 1000, 900 and 790 degrees C isothermal sections of the Al-Pd-Ir phase diagram were experimentally determined. The Al-Pd epsilon-phase region extends up to 22 at.% Ir, the Al4Pd phase dissolves up to 15.5 at.% Ir and the C-Al2,7Ir phase dissolves up to 15 at.% Pd. The Al9Ir2 and Al28Ir9 phases extend up to 2 and 5 at.% Pd, respectively. Two ternary phases were revealed: cubic C-2 (a = 1.5482(2) nm) and hexagonal C-3 (a= 1.09135(14), c = 1.3418(9) nm). The isostructural binary AlPd and AlIr phases probably form a continuous P-range of the CsCl-type solid solutions at the temperatures investigated. (C) 2006 Elsevier B.V. All rights reserved