Claudio Shyinti Kiminami

Topological instability as a criterion for design and selection of aluminum-based glass-former alloys

This letter proposes a criterion to quantitatively correlate chemical composition with crystallization behaviors of Al-based glass-former alloys. By extending to multicomponent systems the topological instability model of Egami and Waseda [J. Non-Cryst. Solids 64, 113 (1984)], we introduce a “lambda (λ) criterion” according to which amorphous alloys with λ>0.1 exhibit glassy behavior, whereas alloys with λ<0.1 are nanocrystalline. Nanoglassy alloys occur when λ≈0.1. A large number of experimental findings in the literature supports the λ criterion, rendering it a useful tool for the design and selection of glass-former systems and compositions.

Corrosion resistance of amorphous and nanocrystalline Fe–M–B (MZr, Nb) alloys

Amorphous Fe‐M‐B (M‚Zr, Nb) based alloys with nanometer-sized crystallites have attracted attention due to their magnetic properties. Although corrosion resistance is a desirable property in such alloys, no study concerning this aspect has been reported. The eAect of metalloid content and partial crystallization on corrosion resistance of Fe‐M‐B (M‚Zr, Nb) amorphous alloys, Fe84Nb7B9 ,F e 84Zr7B9 and Fe83Zr3:5Nb3:5B9Cu1, was investigated. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and thermogravimetric mass gain measurements. The partial crystallization of the amorphous alloy results in a decrease of the corrosion resistance for all the compositions analyzed. We also observed a greater corrosion resistance when Nb was present in comparison to the case when Zr was present. These results are an eAect of the superficial passive film protector formed. ” 2000 Published by Elsevier Science B.V. All rights reserved.

Corrosion resistance of amorphous and polycrystalline FeCuNbSiB alloys in sulphuric acid solution

Abstract The influence of structural changes such as structural relaxation and crystallization on the corrosion resistance of the amorphous Fe74Cu1Nb3Si13.5B8.5 alloy in 0.1M sulphuric acid was investigated. A controlled crystallization of such amorphous alloy leads to nanocrystalline microstructure which increases the corrosion resistance, whereas structural relaxation of amorphous alloy results in reduced corrosion resistance. Different conditions of relaxation (330°C and 380°C) and structural crystallization (554°C and 610°C) were analyzed.

Topological instability and electronegativity effects on the glass-forming ability of metallic alloys

The glass-forming ability (GFA) of metallic alloys is associated with a topological instability criterion combined with a new parameter based on the average electronegativity difference of an element and its surrounding neighbours. In this model, we assume that during solidification the glassy phase competes directly with the supersaturated solid solution having the lowest topological instability factor for a given composition. This criterion is combined with the average electronegativity difference among the elements in the alloy, which reflects the strength of the liquid. The GFA is successfully correlated with this combined criterion in several binary glass-forming systems.

Crystallization and corrosion resistance of amorphous FeCuNbSiB

The influence of metalloid content and thermal treatment on microstructural evolution and corrosion resistance of FeCuNbSiB amorphos alloys with different Si/B ratio was investigated. The crystallization of FeCuNbBSi amorphous alloys is dependent on Si/B content. An increase of the corrosion resistance with the Si content in a 0.1 M H2SO4 solution was observed. The nanocrystallization of alloys, except that with lower Si content, results in an increase of corrosion resistance.

Influence of structural relaxation and partial devitrification on the corrosion resistance of Fe78B13Si9 amorphous alloy

Amorphous alloys obtained by rapid solidification from the melt exhibit a similar structure to those observed in the liquid state, i.e. without long range ordering, in such a way that the constituents of the alloy usually are randomly and homogeneously distributed. Amorphous alloys, depending on their composition, may exhibit interesting characteristics such as very soft magnetic properties and improved resistance to corrosion (1). The high corrosion resistance of these alloys is attributed mainly to a higher rate of dissolution of passivating elements in the amorphous state. In addition, amorphous alloys are chemically homogeneous and free of defects such as grain boundaries, precipitates and segregation, which are favorable sites for corrosion (1). The corrosion resistance of amorphous alloys also depends on their thermal history. Several authors (2, 3, 4) have reported that structural changes, such as structural relaxation and devitrification caused by annealing, change significantly the corrosion properties of these alloys. The Fe78B13Si9 commercial amorphous alloys are produced by the melt spinning process and mainly used as transformer cores owing to their excellent soft magnetic properties, but their resistance to corrosion is poor compared to other commercial amorphous alloys (5). Chattoraj et al. (6) report significant degradation of the magnetic properties caused by corrosion, and conclude that this fact must be taken seriously since, in normal applications, this alloy can rarely be isolated from corrosive agents in the atmosphere. The purpose of this paper is to study corrosion resistance of the amorphous FeBSi alloy and the effects of structural changes such as structural relaxation and partial crystallization caused by annealing.

Amorphous phase formation in spray deposited AlYNiCo and AlYNiCoZr alloys

Al 85 Y 8 Ni 5 Co 2 and Al 84 Y 3 Ni 8 Co 4 Zr 1 (at%) alloy billets were prepared by spray forming. Two ratios of volumetric gas flow rate to mass of metal flow rate (G/M) were used for the Al 85 Y 8 Ni 5 Co 2 alloy (G/M 5 6.4 m 3 /kg and 10.0m 3 /kg) and one G/M (8.7 m 3 /kg) was used for the Al 84 Y 3 Ni 8 Co 4 Zr 1 alloy. The superheat temperature was 1170K and the diameter of the nozzle bore of the atomizer used was 4.4 mm. The molten metal was sprayed at a rate of 3.1 kg/min and nitrogen gas was used for atomization. The resulting billets weighed about 7.0kg and 2.1kg for the Al 85 Y 8 Ni 5 Co 2 and Al 84 Y 3 Ni 8 Co 4 Zr 1 alloys, respectively. The overspray powder was collected in a cyclone separator and accounted for about 19% and 30% of the starting charge for the Al 85 Y 8 Ni 5 Co 2 and the Al 84 Y 3 Ni 8 Co 4 Zr 1 alloy, respectively. The billets and the powder were analyzed by X-ray diffraction using Cu K a radiation (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) system, electron probe microanalysis (EPMA) and transmission electron micros

Amorphous phase formation during spray forming of Al84Y3Ni8Co4Zr1 alloy

Abstract In this investigation the Al84Y3Ni8Co4Zr1 alloy has been processed by spray forming to investigate the potential of achieving substantial fractions of the amorphous phase in the billet. The alloy was prepared by spray metal forming using the ratio of volumetric gas flow rate to mass of metal flow rate of 8.7 m 3 / kg . The resulting billet, weighting 2.1 kg, as well as the powders produced by the particles that had not hit the growing billet (overspray), were characterized by using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powders had particles with spherical morphology in the size range of few microns to 100 μm with the median particle diameters about 20±1 μ m. The resulting billet contained only crystalline phases nevertheless the powder was composed of about 40% volume fraction of amorphous phase. This result indicates that the heating of the billet, by the heat release during solidification of the liquid and semi-solid particles was at temperature and for time enough for crystallization.

Influence of the corrosion on the saturation magnetic density of amorphous and nanocrystalline Fe73Nb3Si15.5B7.5Cu1 and Fe80Zr3.5Nb3.5B12Cu1 alloys

Abstract Amorphous FeMBCu (M=Nb, Zr) and FeNbSiBCu alloys with nanometer size crystallites have attracted attention due to their soft magnetic properties. The mechanism through which crystallization affects the corrosion and the comparative effect of corrosion on magnetic properties of FeMBCu (M=Nb, Zr) and FeNbSiBCu alloys has not yet been evaluated. In this paper the effect of partial crystallization on corrosion resistance of amorphous Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 and Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 alloy ribbons and the comparative effect of corrosion on saturation magnetic flux density, Bs, of these alloys were investigated. The samples were characterized by X-ray diffraction, differential scanning calorimetry and X-ray photoelectron spectroscopy. Corrosion resistance evaluation was carried out by measuring mass loss of samples immersed in 0.1 M H 2 SO 4 solution, and by measuring potentiodynamic polarization curves (potential vs. current). Saturation magnetic flux density, Bs, of the samples were measured. After partial crystallization of Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 amorphous sample the corrosion resistance decreased, while for the Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 the corrosion resistance increased. The decrease of Bs after treatment in the corrosion solution as observed in the nanocrystalline Fe 80 Zr 3.5 Nb 3.5 B 12 Cu 1 sample was larger than that observed for both amorphous and the nanocrystalline Fe 73 Nb 3 Si 15.5 B 7.5 Cu 1 samples after the same treatment.

Amorphous phase formation in Fe-6.0wt%Si alloy by mechanical alloying

Mechanical alloying, MA, is a high-energy ball milling technique, in which elemental blends are milled to achieve alloying at atomic level. This communication describes the results of an investigation on the phase transformation of a mixture of Fe and Si powders with 6wt%Si during MA processing. Besides the verification of the effect of milling time on the structure and on the compositional homogeneity, this study was undertaken in order to confirm, by using TEM technique, the possibility of amorphous phase formation for Si content lower than 17.7wt%.