| The work is dedicated to the problem of forming abilities of stable quasicrystals (QCs) in the Al-based ternary alloy systems.QC is an ordered solid with a non-crystallographic rotational symmetry and quasiperiodic translational order. Metastable QCs were observed in numerous binary alloy systems of Al with transition metals. In general, formation of stable QC requires an additional element. Among known alloy systems those of Al with transition metals (TM) are of a great interest. On the other hand, only a few ternary alloy systems have been studied till now. In order to search for stable quasicrystal under certain empirical criteria guidance instead of by trial and error, in this work, phase equlibria were systematically investigated in the Al-rich parts of the ternary Al-Ni-TM(TM=Mo, Ru) and Al-Co(Rh)-Cu(Ag, Au) alloy systems. Analyzing the characteristics of ternary phase diagrams containing stable QC(s) allows us to discuss: 1) the relationship among the binary metastable QC(s), ternary stable QC(s) and approximant(s); 2) the roles of the third elements in stabilizing metastable QC(s); 3) the compositional region of the ternary stable QC(s); Due to inconsistency in the literature concerning the boundary Al-Ru system the relevant part of this system was reinvestigated.In the literature review, the formation of quasicrystals and approximants in binary and ternary aluminum alloys were compiled.The main experimental results are the following: Al-RuA new orthorhombic Al5Ru2 phase (a=0.78, b=0.66 and c=0.42 nm) isostructural to Al5Fe2 was revealed. The Al6Ru, Al13Ru4, Al2Ru, Al3Ru2 and AlRu phases were confirmed. Transition temperatures were investigated. The AleRu is formed peritectically at 734℃, Al13Ru4 peritectically at 1420℃ and Al2Ru peritectically at 1805℃. Al5Ru2 is formed at 1492℃ by a peritectic reaction of Al2Ru with the liquid and is decomposed at 1340℃ to Al2Ru and Al13Ru4. The Al3Ru2 phase is formed by a peritectoid reaction from Al2Ru and AlRu at 1675℃. Al-Ni-RuThe investigation of this system is to at compare with:Al-Ni-Fe, Fe and Ru belong to the same column in the periodic table,Al-Cu-Ru, Ni and Cu belong to the same period in the periodic table.Phase equilibria were studied in the Al-rich part (>60 at.% Al) of the Al-Ni-Ru alloy system. The decagonal phase with the 1.6 nm periodicity (D4) was confirmed to be stable. Four stable crystalline phases were also determined. They are:cubic (C-Al5(Ru,Ni)2) at about Al71.8Ni11.2Ru17.0 (a=0.7673(1) nm), isostructural to C-Al5Rh2;hexagonal (H-phase) at about Al75.5Ni12.0Ru6.1 (a=1.2132(3) and c=2.7020(9) nm);orthorhombic (O-Al13(Ru,Ni)4) at about Al76.0Ni8.0Ru16.0 (a=l.4960(6), b=0.8253(3), c=l.2668(6) nm), isostructural to O-Al13Co4;monoclinic (m-phase) at about Al81.9Ni8.0Ru16.0(a=0.8636(3), b=0.6333(2), c=0.6273(3) nm, (3=95.12(3), isostructural to Al9Co2.At 1100℃, Al13Ru4 dissolves up to 7.0 at.% Ni. The ternary extensions of Al2Ru, Al6Ru, Al3Ni2 and Al3Ni are below 1 at.%. The ternary stable decagonal phase forms at 1050℃ by a peritectic reaction: Liquid+Al13(Ru,Ni)4+Al3Ni2D4. Together with O-Al13(Ru,Ni)4, C-Al5(Ru,Ni)2 and the H-phase, it is located near the e/a-constant line (e/a=l .86).The isothermal sections at 1100, 1000, 900, 800, 700℃ were built for the compositional range of Al-Al2Ru-AlNi. Al-Ni-MoThe Al-rich part of the Al-Ni-Mo system was investigated in order to compare with that of the Al-Ni-Ru system and clarify the roles of the different transition metals (TMs) in the formation of stable QC (Mo and Ru belong to different columns and the same period in the periodic table).The as-cast and annealed samples (800-1050℃) were studied. No stable ternary QC was observed in the Al-rich part of the Al-Ni-Mo alloy system. The solubility of Ni in Al-Mo binary phases and of Mo in Al-Ni binary phases is quite low.Two stable ternary crystalline phases were observed:An orthorhombic X-phase (a=1.0054(4), b=l.5288(4) and c=0.8519(2) nm atTetragonal, isostructual to...
|
PDF Full Text Request