Abstract:
Quasicrystals (QC´s) exhibit particular features when compared to a conventional crystalline solid materials. They present an aperiodic, however, highly ordered atomic structure. These phases exhibit a variety of interesting properties for application as protective coatings, including high hardness, low friction coefficient, high corrosion resistance in acid medium, high resistance to oxidation and low thermal conductivity. In the present work, several aluminum based alloys in the systems Al-Fe-Cu, Al-Cu-Fe-Cr, Al-Cu-Fe-Ni, Al-Ni-Co, Al-Ni-Co-Cr, Al-Ni-Co-Cu and Al-Co-Fe-Cr have been assessed, with the objective to develop new quasicrystalline compositions with improved corrosion, thermal and tribological properties.
Rapid solidification methods, such as melt-spinning, atomization, HVOF and arc melting, were used. The microstructures were characterized by transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Evaluation of the properties included mechanical and pin-on-plate wear tests and Vickers Microhardness. Al-Cu-Fe and Al-Co-Ni are systems well known for the formation of quasicrystalline phases and the present work aimed to modify ternary quasicrystalline compositions of those alloys by adding corrosion resistant elements, such as Cr, Ni and Cu. The Al-Co-Fe-Cr system was studied due to their known good thermal insulation properties.
Quasicrystalline phases were observed in most alloys of the Al-Cu-Fe-(Cr,Ni) and Al-Ni-Co-(Cr,Cu) systems. The Al-Co-Fe-Cr system did not present the formation of quasicrystalline phases; instead, we observed the formation of two intermetallic phases, which are quaternary extensions of Al5Co2 and Al13Co4 phases. The coatings fabricated from this alloy presented extremely low friction coefficient values and Vickers microhardness around 500 HV in the coating material and up to 1000 HV in the bulk material. The results from this assessment of potential quaternary quasicrystalline alloys indicated a promising way of tailoring new quasicrystalline compositions with improved properties such as corrosion behavior, thermal insulation and low friction coefficient, which are desirable properties for coating applications.
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