We use x-ray photon correlation spectroscopy to investigate the structural relaxation process in a metallic glass on the atomic length scale. We report evidence for a dynamical crossover between the supercooled liquid phase and the metastable glassy state, suggesting different origins of the relaxation process across the transition. Furthermore, using different cooling rates, we observe a complex hierarchy of dynamic processes characterized by distinct aging regimes. Strong analogies with the aging dynamics of soft glassy materials, such as gels and concentrated colloidal suspensions, point at stress relaxation as a universal mechanism driving the relaxation dynamics of out-of-equilibrium systems.

Calorimetric data of primary crystallization is usually interpreted in the framework of the Kolmogorov [Dokl. Akad. Nauk SSSR 1, 355 (1937)], Johnson and Mehl [Trans. AIME 135, 416 (1939)], and Avrami [J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941)] (KJMA) theory. However, while the KJMA theory assumes random nucleation and exhaustion of space by direct impingement, primary crystallization is usually driven by diffusion-controlled growth with soft impingement between the growing crystallites. This results in a stop of the growth before the space is fully crystallized and induces nonrandom nucleation. In this work, phase-field simulations are used to check the validity of different kinetic models for describing primary crystallization kinetics. The results show that KJMA theory provides a good approximation to the soft-impingement and nonrandom nucleation effects. Moreover, these effects are not responsible of the slowing down of the kinetics found experimentally in the primary crystallization of glasses.

Random subdivisions in a $D$-dimensional Euclidean space are commonly observed in many scientific fields, such as metallurgy, geology, biology, and even, in the case of large $D$, in subjects related to information codification. This paper presents an analytical approximation of the size probability distribution in space subdivisions generated by random point processes, which include the well-known cases of the Poisson-Voronoi and the Johnson-Mehl cellular structures. Based on the calculations of Gilbert [Ann. Math. Stat. 33, 958 (1962)] and an assumption for the distribution shape, the cell size distributions are obtained in a general way for a very wide range of random space subdivisions.

The effect of low amounts of Cr on glass forming ability and corrosion behavior of Fe(65-x)CrxMo14C15B6 (x = 0, 2, 4, 6, 8,10 at.%) ribbons have been studied. It was found that the reduced glass transition temperature (T-rg) do not change significantly with Cr content. The glass forming ability (GFA) of this system is evaluated by the gamma(m), delta and omega parameters and the alloys containing 4 and 6 at.% were found to be the best glass formers in this system. The temperature interval of the supercooled liquid region (Delta T-x) changed with Cr and was enlarged from 35 K at x = 0 to 50 K at x = 4. Corrosion rates measured by immersion tests in H2SO4 decreased with an increase of chromium content in the alloys. The electrochemical measurements indicate that the alloys containing more than 4 at.% of Cr are spontaneously passivated with low current densities in 0.1 N H2SO4 whereas the alloys with Cr content <4 at.% showed transpassive Mo dissolution. In view of these results, the optimal amount of Cr addition in Fe-Mo-C-B amorphous steels is discussed. (C) 2014 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (published version

We report here on a polyamorphic-phase transition upon application of pressure on a Ce-based metallic glass, Ce${}_{70}$Al${}_{10}$Ni${}_{10}$Cu${}_{10}$, investigated by x-ray diffraction and inelastic x-ray scattering. This alloy is found to display a strong hysteresis in volume per atom upon application and subsequent release of pressure. The observed structural changes are correlated with changes observed by inelastic x-ray scattering in the elastic constants, acoustic mode frequencies, and sound speed. The results reported here point toward three different amorphous phases for this alloy existing in the 0–25 GPa pressure region: low- and high-density states and an intermediate mixed state that displays a hysteresis behavior. Finally, we discuss the impact of Ce concentration on the polyamorphic transition for a series of Ce-based metallic glass alloys and link it to the phase transformation between $\gamma$-Ce and $\alpha$-Ce under pressure.