Jorge M. Cubero-Sesin

High strength and high electrical conductivity of UFG Al-2%Fe alloy achieved by high-pressure torsion and aging

In this study, Al-2%Fe samples extracted from a cast ingot in the shape of rings were processed by High-Pressure Torsion (HPT) at room temperature. Suitable specimens were extracted for evaluation of mechanical properties and electrical resistivity. High tensile strength of ~600 MPa was attained by HPT due to grain refinement down to an average grain size of ~130 nm and by subsequent aging accompanied by nano-sized (~10 nm) AhFe precipitates. The resulting conductivity (IACS%) was recovered from ~40% in the steady state after HPT to well above 50% in the peak-aged condition, which is in the range of current Al electrical alloys.

Aging and Precipitation Behavior in Supersaturated Al-2%Fe Alloy Produced by High-Pressure Torsion

The aging behavior of a cast Al-2 wt.% Fe alloy processed by High-Pressure Torsion (HPT) at room temperature was studied by subsequent aging treatments at 200 °C. Observations by Transmission Electron Microscopy (TEM) revealed that the microstructure after HPT processing reached an ultrafine-grained level with an average grain size in the Al matrix of ~120 nm. The initial eutectic structures were fragmented into particles with sizes of less than 400 nm and partially dissolved in the matrix up to a supersaturated Fe content of ~1% as confirmed by X-Ray Diffraction (XRD) analysis. The peak-age condition was achieved within 0.25 h of aging, which provides the maximum hardness of ~200 HV. Analyses by high-resolution S/TEM show that round particles of Al6Fe with sizes of ~5-10 nm and semi-coherent with the matrix are the dominant precipitates in the peak-aged condition. The hardness increases by aging for 12 h above the as-HPT-processed level of 185 HV. The dominant precipitate phase transforms to Al3Fe in the over-aged condition with a loss of coherency during growth. Enhanced precipitation kinetics was observed because of high density of lattice defects induced by the HPT processing, which were also confirmed by significant recovery in the electrical conductivity of the samples after aging.

Simulación del procesamiento de una aleación de Ti-6Al-7Nb por la técnica de presión en canal angular constante usando el método de elementos finitos

In this work, the finite element method was used to analyze plastic deformation of a bar of Ti-6Al-7Nb with a squared cross section of 10 x 10 mm2 processed by equal-channel angular pressing (ECAP). Firstly, this process was simulated for different internal angles and internal and external radii of curvature of the channel, by a simplified 2D model. The influence of these parameters on the magnitude and homogeneity of the deformation, as well as on the applied load, was determined. From the 2D simulation results, optimum curvature radii for each internal angle was selected, based on a proposed design for the external dimensions and material of the ECAP processing die. Furthermore, it was determined by 3D simulation that the selected dimensions and material for the die are sufficient to withstand the high pressures involved in this process.

Superplasticity of nanostructured Ti-6Al-7Nb alloy with equiaxed and lamellar initial microstructures processed by High-Pressure Torsion

Microstructural modifications of a biomedical Ti-6Al-7Nb alloy were accomplished via heat treatment in 3 different quenching mediums and then processed by High-Pressure Torsion (HPT) at room temperature. The microstructure of the as-received condition is composed of an equiaxed duplex (α+β) structure. After the heat treatment, a combination of primary α phase and lamellar structures was obtained with an increasing fraction of the martensitic lamellar with increasing cooling rate. After HPT processing, refinement of the microstructures was observed for N=5 revolutions. Transmission electron microscopy (TEM) of the sample quenched in liquid nitrogen confirmed the nanostructure with grain sizes below 100 nm and high density of lattice defects after HPT processing for N=5 revolutions. High-temperature tensile tests were carried out at 800 °C with an initial strain rate of 2×10−3 s−1 on specimens with different combinations of heat treatment and HPT straining. The test in the as-received condition presented a maximum elongation to failure of ~400% after HPT processing for N=5 revolutions. The highest elongation to failure in the heat-treated samples was ~580% in the sample quenched in liquid nitrogen and processed for N=5 revolutions.