The effect of chromium and nickel as alloying elements on rapidly solidifying alloys of the Al-Cu-Fe system is investigated. Four different compositions were selected for the analysis: Al63Cu18Fe10Ni9, AlCu20Fe13Ni3, Al65Cu22Fe10Cr3 and Al67Cu20Fe5Cr8, based on maintaining a constant average number of valence electrons per atom (e/a) in the ternary Al-Cu-Fe quasicrystal. Tapes of these alloys obtained by melt spinning were subjected to detailed analysis using X-ray diffraction, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the icosahedral quasicrystalline phase of Al-Cu-Fe has limited nickel solubility. With increasing Ni content, a sharp decrease in the proportion of the quasicrystalline phase is observed, replaced by two primitive cubic B2 phases. The introduction of chromium promotes the formation of a decagonal quasicrystalline structure, displacing the icosahedral one. At a Cr concentration of 3 at.%, both quasicrystalline phases coexist, but the icosahedral one predominates. The alloy containing 8 at.% Cr is characterized by the presence of an exclusively decagonal phase.
Over the past decades, more than a hundred metallic systems capable of forming quasicrystalline phases have been identified. These include Al-Cu-Fe, Al-Cr-Fe, Al-Cu-Fe-Cr, Al-Co-Ni, Al-Cr-Ni-Co, Al-Mn, and others. Complex intermetallic phases, which are quasicrystalline approximants, are often found in alloys close in composition to quasicrystals. They have a similar atomic structure and functional properties, such as high hardness, low friction coefficient, good corrosion resistance, and low thermal conductivity.
The ternary Al-Cu-Fe system is the most studied quasicrystal. Annealing or high cooling rate, such as melt spinning, are required to obtain a single-phase Al-Cu-Fe quasicrystal. The cubic τ-AlCu(Fe) phase is also often found in Al-Cu-Fe melt-spinning tapes. Addition of chromium to quasicrystalline Al-Cu-Fe alloys results in the formation of a decagonal quasicrystalline phase and improves corrosion and oxidation resistance. The aim of this work is to study the effect of Ni and Cr additives on the formation of quasicrystalline phases in the Al-Cu-Fe-Ni and Al-Cu-Fe-Cr systems, as well as to determine the composition ranges in which decagonal and icosahedral phases are observed in the Al-Cu-Fe-Cr system.
The effect of transition metals (M = Cr, Ni) on the structure and thermal stability of the quasicrystalline phase in rapidly solidified Al-Cu-Fe tapes was studied. Tapes of Al62Cu25.5Fe12.5 and Al62Cu25.5Fe12.5-xMx (x = 1, 2; M = Cr, Ni) alloys were obtained by melt drawing. X-ray phase analysis and differential scanning calorimetry showed that the addition of chromium or nickel promotes the formation of the icosahedral quasicrystalline phase (i-phase) in the cast state.
It is shown that alloys containing chromium have higher thermal stability of the i-phase compared to alloys alloyed with nickel. This is manifested in an increase in the crystallization temperature of the metastable i-phase. It is found that small additions of chromium (x = 1) lead to a more pronounced stabilization effect than additions of nickel. It is assumed that chromium, which has a larger atomic radius compared to nickel, has a greater effect on the structure and stability of the quasi-crystalline lattice. The results obtained can be used to develop new materials with improved properties based on quasicrystals.
Author: W. Wolfa, F. G. Coury, M. J. Kaufman, C. Bolfarini, C. S. Kiminami, W. J. Botta
Institute: Postgraduate Program in Materials Science and Engineering, Federal University of São Carlos, Rd. Washington Luis, km 235, 13565-905, São Carlos, São Paulo, Brazil, Department of Metallurgy and Materials Science, Colorado School of Mines, Golden, Colorado 80401, USA, Department of Materials Science, Federal University of Sao Carlos, Road Washington Luis, km 235, 13565-905, Sao Carlos, Sao Paulo, Brazil