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Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co-Cr-Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin ε (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The ε-lamellae grown on the {111}γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

Optical surface second harmonic measurements of isotropic thin-film metals: Gold, silver, copper, aluminum, and tantalum Phase formation has been studied in Au-AI thin-film interactions by means of 4 He+ MeV backscattering and x-ray diffraction techniques. The films were annealded at temperatures low enough for no liquid phase formation. Au 4 Al, AU s AI2' Au 2 Al, AuAl, and AuAl 2 were detected from samples prepared by depositing the exact stoichiometry quantities of Au and AI. The phase formation sequence was determined. The first phase formed is Au s A1 2 ; the others are observed with the disappearence of one phase previously formed. For instance, Au 4 Al grows only when all Al is reacted and, on the other hand, AuAl 2 when all Au is reacted. The sequence of the phases in the Au-AI interactions cannot be interpreted on the basis of pure thermodynamic or kinetic arguments and a composite mechanism is proposed.

Phase formation at temperatures well below the melting point of the phases was studied in thin silicon–near-noble-metal films by means of 4He+ ion-backscattering spectrometry and x-ray diffractometry in SiO2/Si/M film systems, where the metal-film thickness was larger than that of the Si film. In the initial stage of compound formation where both unreacted Si and M layers are present, the M2Si phase has been found. At increasing annealing times and temperatures, more and more metal-rich phases have been detected. The Si-Ni thin-film system evolution follows exactly the phase diagram reported in the literature; moreover, for Ni, Pt, and Pd-Si thin-film interactions the end phases are dictated by the phase equilibrium and can be predicted by the phase diagrams.

Extended x-ray absorption fine structure spectroscopy, x-ray diffraction and transmission electron microscopy were used to analyze the Nb coordination and clustering in Nb-doped (5 at. %) h-Mg film samples deposited by rf magnetron sputtering. Results show that the catalytic effect of the Nb doping in the H-2 absorption and desorption kinetics is connected with the formation of Nb nanoclusters dispersed in the host matrix. The H-2 desorption from beta-MgH2 is favored by local elastic stresses produced by beta-NbH0.89 clusters on the MgH2 matrix that reduces the stability of the hydride phase and by preferential paths in the nanocomposite hydride