Melt drawing, also known as spinning, is an effective way to produce rapidly quenched materials with a unique microstructure. When applied to Al-Cu-Fe-(M=Cr,Ni) alloys, this method allows the formation of tapes containing a quasi-crystalline phase distributed in an amorphous or crystalline matrix. By varying the cooling rate, it is possible to control the size and volume fraction of quasi-crystals, as well as the phase composition of the tapes.
Addition of chromium or nickel to the Al-Cu-Fe alloy has a significant effect on the formation of quasicrystals. Chromium, as a rule, promotes an increase in the supercooling of the melt, which leads to the formation of a larger number of crystallization centers and, consequently, to a decrease in the size of the quasicrystals. Nickel, on the contrary, can stabilize the icosahedral phase and promote its growth, which leads to the formation of larger quasicrystals.
The effect of alloying with chromium and nickel on rapidly solidifying alloys of the Al-Cu-Fe system is studied. Four compositions were selected for analysis: AlCu20Fe13Ni3, Al63Cu18Fe10Ni9, Al65Cu22Fe10Cr3 and Al67Cu20Fe5Cr8. The choice was based on maintaining a constant average number of valence electrons per atom (e/a) in the ternary Al-Cu-Fe quasicrystal. Tapes from these alloys were obtained by melt spinning and studied by X-ray diffraction, transmission electron microscopy and energy-dispersive X-ray analysis.
The results show that the icosahedral quasicrystalline phase of Al-Cu-Fe is characterized by limited solubility of nickel. Consequently, with increasing nickel content, there is a sharp reduction in the proportion of the quasicrystalline phase, giving way to two primitive cubic phases of the B2 type. The introduction of chromium leads to the formation of a decimal quasicrystal at the expense of the icosahedral phase. At a chromium concentration of 3 at.%, the coexistence of the icosahedral and decimal phases is observed, with the former dominating in volume fraction. In the alloy with a chromium content of 8 at.%, only the decimal phase was identified.
The microstructure of melt-pulled Al-Cu-Fe-(M=Cr,Ni) tapes is investigated using various techniques, including transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM allows visualization of quasicrystals and determination of their size, shape and orientation, while XRD is used to identify the phase composition of the tapes and determine the lattice parameters.
The properties of Al-Cu-Fe-(M=Cr,Ni) tapes containing quasicrystals depend on their microstructure. As a rule, such tapes have high hardness, corrosion resistance and a low friction coefficient. Due to these properties, they are used in various fields, including protective coatings, wear-resistant parts and catalysts.
Author: W. Wolf, 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, R. Washington Luis, km 235, 13565-905, São Carlos, São Paulo, Brazil, Department of Metallurgy and Materials Science, Colorado School of Mines, Golden, CO 80401, USA, Department of Materials Science, Federal University of São Carlos, R. Washington Luis, km 235, 13565-905, São Carlos, São Paulo, Brazil