Bulk glassy and nonequilibrium crystalline alloys by stabilization of supercooled liquid: fabrication, functional properties and applications (Part 2)

Abstract

Magnetic properties. Although glassy alloys inFe-and Co-based systems exhibit good soft magnetic properties, the characteristics are expected to be nearly the same as those for amorphous alloys, which require high cooling rates (> 10 5 K/s) for their formation.Recently, it has been found that the soft magnetic properties of Fe-and Co-based glassy alloys are much superior to those for Fe-and Co-based amorphous alloys.1)-3) Figure 1 summarizes the relationship between coercivity (H c ) and the ratio of saturation magnetostriction (λ s ) to saturation magnetic flux density (J s ) for Fe-based glassy alloys, together with data for Fe-based amorphous alloys. A rather good linear relationship is recognized for both alloy groups, which can be expressed as H c ∝ λ s /J s . It is known that the gradient in the relationship between H c and λ s /J s depends on the volume and density of internal defects, i.e., structural inhomogeneity in their alloys. 4) As seen in Fig. 1, the gradient of Fe-based glassy alloys is much smaller than that of Fe-based amorphous type alloys, indicating that the Fe-based glassy alloys have more homogeneous atomic configurations with lower volumes and densities of internal defects than ordinary Fe-based amorphous type alloys produced at much higher cooling rates. It is therefore concluded that the formation of these more homogeneous atomic configurations is the origin of the lower coercivity of Fe-based glassy alloys. Reflecting the lower coercivity, the Fe-based glassy alloys exhibit much higher permeability than Febased amorphous alloys, in conjunction with a rather high saturation magnetization of 1.2 -1.5 T. With their good soft magnetic properties, the Fe-based glassy alloys have been used as consolidated magnetic cores of common mode choke coils and noise filters for electrical power supplies through the development of an inexpensive mass-production process consisting of water atomization, followed by mixing with insulating and lubricating materials, drying, crushing, classification, forming and then heat treatment. Abstract: The novel stabilization phenomenon of supercooled liquid in special multi-component metallic alloys that follow the three component rules has enabled us to fabricate a number of bulk glassy and nonequilibrium crystalline alloys exhibiting useful characteristics. Following the previous review (Part 1; Proc. Jpn. Acad. Ser. B 81, 156-171), this paper (Part 2) reviews our recent results on the physical, chemical, mechanical and magnetic properties of the resulting bulk nonequilibrium materials including glassy single phase alloys, nanocrystal-, nanoquasicrystal-and dendritic crystal-dispersed glassy alloys and nanocrystalline alloys. Finally, the application potential of bulk glassy alloys is addressed, taking account of their novel engineering properties and production processes.

Ni-based amorphous alloy membranes for hydrogen separation at 400°C

“…Crystalline Pd-alloy membranes are the state-of-the-art in alloy membranes by virtue of their high H 2 permeation rates and stability in hydrocarbon and synthesis gas streams [4], however amorphous alloy membranes, composed primarily of inexpensive elements such as Ni and early transition metals (ETMs), are of considerable interest as a low-cost alternative [6]. In addition, these materials can be produced in large quantities using planar flow casting [7], an established technique used in the production of other rapidly solidified alloys (most notably soft magnetic materials for transformer coils). Given these favourable characteristics, these amorphous alloy membranes are of particular interest for the large-scale production of H 2 from carbon-based fuels.…”

Compressive Plasticity of Zr-Based Bulk Metallic Glass at Low Temperature

“…Bulk metallic glasses (BMGs) alloys possess ultra-high strength, super-elasticity, high fracture toughness, excellent wear and corrosion resistance, therefore they are considered as potential structural materials [1][2][3][4][5]. The mechanical properties of BMGs have been extensively studied at room temperature and above.…”

Metallic glasses : thermal, mechanical properties and their correlation.

“…Soft magnetic MGs with low coercivity and high electrical resistivity are very suitable for transformer cores. Fe-Al-Ga-P-C-B-Si glassy alloy powders prepared by Yoshida et al [135] were made into a core which has a constant permeability of about 110 up to 10MHz in comparison to commercial cores and a very low core loss of 610 kW/m 3 in a magnetic field of 100 kHz, 0.1 T. Based on these distinguished high frequency magnetic properties, magnetic-shielding sheets for laptops were fabricated [136].…”