J.M. Loureiro

Order-disorder phenomena from X-ray diffraction in FeCo alloys annealed and ground at high energy

Order-disorder transformations were studied in annealed and high-energy ball-milled near-equiatomic FeCo alloys. X-ray diffraction with Co K α radiation enables to follow disordering with milling time because of anomalous dispersion.

Mechanically Driven Dissolution of Sn in Near-Equiatomic Bcc FeCo

Ternary alloys, (Fe50−x/2Co50−x/2)Snx (x ≤ 33 at.%), are prepared by mechanical alloying from powder mixtures of the three elements. As-milled alloys are studied by X-ray diffraction and 57Fe and 119Sn Mössbauer spectroscopy. The solubility of Sn in near-equiatomic bcc FeCo is increased from ~0.5 at. % at equilibrium to ~20 at.% in the used milling conditions. The average 119Sn hyperfine magnetic field at room temperature is larger, for any x, than the corresponding fields in mechanically alloyed Fe-Sn solid solutions.

Long-time ball milling of FeCr

Near-equiatomic sigma and alpha phases of the FeCr system were ball-milled in vacuum in a vibratory mill for long times. When milled, the sigma phase first transforms into an alpha phase, which amorphises partially as observed too when milling directly an alpha phase. In the latter case, the amorphisation rate of the alpha phase is about five times smaller than it is when the alpha phase is formed under milling from the sigma phase. In both experiments, the amorphous phase fractions formed during long periods of milling are independent of the rate of amorphisation.

Long ball-milling of bcc-FeCr at different injected powers: Amorphization and partial crystallization

The structural changes induced by long ball-milling of the α-FeCr bcc phase in vacuum in a vibratory Fritsch P0 mill at two different amplitudes, were studied by Mossbauer spectroscopy and X-ray diffraction. In previous studies we showed that amorphization is an intrinsic phenomenon which occurs when grinding alpha and sigma phases of near-equiatomic FeCr alloys. With long periods of milling at different injected powers, we observe a phenomenon of amorphization-partial crystallization-amorphization which is reminiscent of the cyclic amorphization-crystallization phenomenon that takes place in various ball-milled alloys.

Magnetic study of amorphization of ball-milled FeCr alloys

The magnetization of sigma and alpha FeCr samples ball-milled in vacuum is reported as a function of milling time. The change of the saturation magnetization with milling time is non-monotonous in the sigma series: after an initial increase due to the transformation to the magnetic alpha phase, then it decreases as in the alpha phase. The results are fully consistent with our previous results from Mossbauer spectroscopy that established the formation of an amorphous phase.