Dissertation consists of results on research of structure changes and phase transformations in alloys of aluminium with 3d- and 5d- transition metals, obtained by quenching of melts and by arc melting with further homogenizing annealing.
It is shown that ternary alloys, concentration of which is expressed by formula Al90+хFe3Nb4+х upon quenching are amorphous with distinct “molecular clusters”, centred by transition metal atoms, distributed regularly in bulk of alloy. By combination of high temperature X–ray diffraction and Mӧssbauer spectroscopy methods it was revealed that crystallization of such alloys has three stages. First of them is related with extraction of nanocrystalline Al in amorphous matrix and second one with formation of two intermetallides: Al3Nb compound and Al6Fe metastable phase. Appearance of new type of magnetic ordering, revealed at 700 K, is due to cooperation of layers of Al6Fe phase by Fe-atoms with nearest almost spherically symmetric arrangement of Al-atoms. As result the formation of Al13Fe4 (Al3Fe) crystalline compound with Penrose quasicrystalline cell like structure. Such structural transformations are confirmed by scanning electron microscopy. The crystallization of alloy is accompanied by drastic decrease of integral microhardness from 1900 MPa in amorphous state to ~ 800 MPа after crystallization of three compounds.
It was shown that in ternary Al100-3xV2xFex alloys at rapid quenching it is possible the competition of two icosahedral quasicrystalline phases. Particularly the sample of Al94V4Fe2 contains only two coexisting phases with different quasicell parameter of content, corresponding formulas Al86V9,3Fe4,7 and Al86V4,3Fe9,7. It is shown that increase of total content of transition metal promotes the formation of the phase with higher value of quasicell parameter and amorphous phase that is supposed to be caused by structural competition at quenching of alloy. Total microhardness significantly depends on content of alloys and increases gradually from 867 up to 3000МPа with increasing of total content of transition metals from 6 to 12 аt. %.
The Al-enriched alloys of Al–Ni–Zr(Hf) systems, synthesized by rapid quenching are found to be brittle and partly or particularly amorphous. Metallic ribbons of Al84Ni8Zr8(Hf8) content consist of three phases: Al, NiAl3 and ZrAl3 or HfAl3, respectively. The same ternary phase equilibrium was revealed in casted Al84Ni8Zr8 alloy, not observed in annealed samples. As the result of phase equilibria studies in Al-enriched corner of phase diagram we have revealed the existence of notable homogeneity regions for ZrNi2Al5 and Zr6Ni8Al15 compounds. At first it was pointed out that formation of Zr6Ni8Al15 compound occurs according to eutectoid reaction Zr6Ni8Al15 ↓ NiAl + ZrNixAl2-x (structure type – MgCu2). Unknown early ternary equilibrium between phases: Zr6Ni8Al15 – NiAl – ZrNixAl2-x was observed at two temperatures.
Alloys of Al–Ni–Zr(Hf) systems, which corresponds to pseudobinary Laves phases of ST MgCu2 and MgZn2 have been obtained in partly amorphous state by means of mechanical treatment in hydrogen atmosphere. Besides, we have obtained the nanocrystals of the Laves phase, whose size ≈ 6-14 nm, embedded in amorphous matrix. In case of alloys with Hf further amorphization with decomposition into HfH2, AlH3 hydrides and nanocrystalline nickel at heating to 873 K. Such sequence of phase transformations was established by means of X–ray diffraction and magnetic phase analysis. The result of hydrogen saturation of Laves phases is appearance of magnetic properties. We supposed that it is caused by change of electron structure of Laves phases. Hydrogen, possessing by higher electronegativity attract electrons from Ni-atoms that results increasing of their magnetic moment.
Temperature dependences of specific electroresistivity of ternary compounds in Al–Ni–Zr(Hf) systems reveal metallic behaviour with tendency to saturation at high temperatures and can be interpreted by Bloch-Grüneisen-Mott model. Such behaviour is caused by 3d- electrons of Zr, Hf and Ni– atoms. It was at first revealed for Zr(Hf)NixAl2-x (ST – MgCu2) Laves phases the occurrence of superconductive transitions at temperatures 1,5 K and 0,9 K respectively at concentrations, corresponding the most low concentration of Ni within homogeneity ranges. Contrary, at maximum concentration it is observed Kondo-like behaviour, that is manifested by slight increasing of electroresistivity at approaching to temperature T=0K.
