Search

The performance of Ti alloys can be considerably enhanced by combining Ti and other elements, causing an eutectic transformation and thereby producing composites in situ from the liquid phase. This paper reports on the processing and characterization of a directionally solidified Ti–Fe eutectic alloy. Directional solidification at different growth rates was carried out in a setup that employs a water-cooled copper crucible combined with a voltaic electric arc moving through the sample. The results obtained show that a regular fiber-like eutectic structure was produced and the interphase spacing was found to be a function of the growth rate. Mechanical properties were measured using compression, microindentation and nanoindentation tests to determine the Vickers hardness, compressive strength and elastic modulus. Directionally solidified eutectic samples presented high values of compressive strength in the range of 1844–3000 MPa and ductility between 21.6 and 25.2%.

The Al46Cu23Fe13 quasicrystal phase, prepared by arc-melting and nanostructured using high energy ball milling technique, was studied employing X-ray diffraction, transmission electron microscopy, ferromagnetic resonance and electric transport measurements. Fe local environments were studied by Mossbauer spectroscopy. The resistivity ratio R(4.2 K)/R(300 K) is within the expected values commonly observed in an icosahedral phase. In general, the experimental results show that an appropriate heat treatment of the as-cast alloy prepared by arc-melting makes possible to obtain good quasicrystal samples. On the other hand, for milling time longer than five hours, the average grain-size of quasicrystal phase reduces, but it preserves Fe local atomic orders. It is also observed that the quasicrystalline sample decomposes in an iron rich nano-quasicrystalline phase and a e-Al2Cu3 phase. Electric transport measurements show that at low temperatures the nano-quasicrystalline samples behave strongly different to their solid counterparts, an effect attributed to a long-range order reduction and an increasing of grain boundary regions. The presence of local magnetic moments in the nanostructured sample is also discussed.

An extremely fast hardening response with no reduction in peak hardness was obtained in Al–Cu with minor additions of Si and Ge by 8% plastic deformation before artificial aging. The mechanism for the accelerated hardening was determined by detailed characterization with transmission electron microscopy. Plastic deformation was found to enhance the nucleation rate of Si–Ge precipitates, resulting in a higher volume density. Such precipitates catalyzed the formation of θ′ precipitates that are responsible for hardening.

Nanocrystalline Al64Cu23Fe13 icosahedral quasicrystal has been obtained by milling of solid quasicrystal precursors prepared by arc-melt. The local structure around Fe atoms was studied by Mossbauer spectroscopy using a quadrupole splitting distribution method. Mossbauer results of annealed and milled samples show the existence of a broadened distribution of Fe sites which is associated to intrinsic disorder. The structural characterization was determined using x-ray diffraction. The average grain-size of the nanostructured quasicrystal, obtained from the line broadening of the X-ray diffraction peaks, was estimated to be of the order of 10 nm for a sample milled by 5 h.