Obtenção de ligas estequiométricas quasicristalinas de base alumínio contendo nióbio e/ou manganês

Abstract

Quasicrystalline alloy systems are sensitive to the addition of other elements and variations in processing methods. This sensitivity produces a wide network of substitutions that can be performed to improve certain properties of these systems, in order to satisfy specific application demands. In this work, quasicrystalline aluminum-based alloys were produced, with total stoichiometric replacement of Chromium by Niobium and addition of Manganese in the AlCuFe ternary system. The ability of these new alloy systems to form a quasicrystalline phase was observed. The alloys of composition Al72Mn15Nb5Si8 and Al61.7Cu10Fe8.5Mn1.0 were quickly solidified via meltspinning and the alloy Al71Cu10Fe8.5Nb10.5 obtained by casting in a vacuum furnace. The microstructures were analyzed by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (MET) and X-ray Diffractometry (XRD) and, the thermal stability of the phases was evaluated through Differential Thermal Analysis (ATD). It was possible to obtain a quasicrystalline phase in all alloy systems obtained, both presented a mixture of quasicrystalline phase with one or more crystalline and/or amorphous phases. In fact, it was possible to state that it is possible to obtain the quasicrystalline phase for all alloy systems with the processing method used. After rapid solidification via meltspinning carried out in the Al72Mn15Nb5Si8 and Al61.7Cu10Fe8.5Mn1.0 systems, the alloys appeared in the form of discontinuous pieces of ribbons with equiaxed grains and varying sizes. In the alloys of the Al-Mn-Nb-Si and Al-Cu-Fe-Mn systems, after heat treatment via meltspinning, it was possible to observe the presence of the icosahedral quasicrystalline phase Al (Mn,Si) dispersed in an amorphous matrix and AlCuFe together with other crystalline phases, respectively. In the raw Al71Cu10Fe8.5Nb10.5 alloy, the beginning of the formation of regular polyhedra can be observed in some regions, it was possible to observe in some regions the beginning of the formation of regular polyhedra that may be associated with the formation of the quasicrystalline phase. The results indicate that the quasicrystalline phase can be obtained by the systems studied and that its presence can occur in conjunction with other crystalline or amorphous phases.