Baolong Shen

Ductile Co–Nb–B bulk metallic glass with ultrahigh strength

Abstract A ternary Co 61 Nb 8 B 31 bulk metallic glass with plasticity of 5% and yield strength of 5200xa0MPa was fabricated. It is shown that the primary crystallization product of the Co 61 Nb 8 B 31 glass is the vertex- and edge-sharing Co 2 Nb type phase. The enhanced plastic strain is consistent with the observed multiple shear bands that can redistribute the internal shear stress. The appreciable plastic strain favors the formation of metallic bonding network-like structure and holds high Poissons ratio.

Correlation of atomic packing with the boson peak in amorphous alloys

Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.

The effect of Ni addition on microstructure and soft magnetic properties of FeCoZrBCu nanocrystalline alloys

(Fe0.7Co0.3-xNix)88Zr7B4Cu1 nanocrystalline alloys were developed with the aim of improving the magnetic properties while keeping high Curie temperature (TC). It was revealed that Ni addition inhibited the precipitation of metastable fcc-(Fe,Co,Ni) phase hence increased thermal stability. Although the saturation magnetic flux density (Bs) showed a slight decrease, uniform nanostructure with small grain size and high volume fraction of crystals was formed with increasing Ni addition. As a result, the (Fe0.7Co0.3-xNix)88Zr7B4Cu1 nanocrystalline alloys exhibited excellent magnetic properties with a high Bs of 1.54-1.79 T, low coercivity (Hc) of 17-20 A/m and low core loss of 9.1-11.1 W/kg at 1 T and 400 Hz. The combination of high TC of 747-972 °C, low core loss as well as low material cost promised this FeCoNiZrBCu alloys broad application prospect at high temperature.

Effect of magnetic field annealing on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys with low permeability

The effect of transverse magnetic field annealing (TFA) on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys was investigated with the aim of reducing effective permeability (μe). It was revealed that the increasing B content improved thermal stability, increased saturation magnetic flux density (Bs) of as-quenched alloys, while the samples exhibited a slightly larger coercivity (Hc) when the atom percentages of Si and B were similar. Permeability decreased dramatically after TFA. The decrease of permeability mainly depended on annealing temperature and magnetic field intensity. Besides, flat hysteresis loops were obtained after TFA, Lorentz micrograph observation revealed the TFA sample exhibited denser magnetic domain walls, which confirmed it was more difficult to be saturated. The Co71Fe2Si9B14Mn4 alloy was successful prepared with low μe of 3020, low Hc of 1.7 A/m and high resistance to DC bias 6 times that of as-quenched alloy at the DC field of 300 A/m.The effect of transverse magnetic field annealing (TFA) on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys was investigated with the aim of reducing effective permeability (μe). It was revealed that the increasing B content improved thermal stability, increased saturation magnetic flux density (Bs) of as-quenched alloys, while the samples exhibited a slightly larger coercivity (Hc) when the atom percentages of Si and B were similar. Permeability decreased dramatically after TFA. The decrease of permeability mainly depended on annealing temperature and magnetic field intensity. Besides, flat hysteresis loops were obtained after TFA, Lorentz micrograph observation revealed the TFA sample exhibited denser magnetic domain walls, which confirmed it was more difficult to be saturated. The Co71Fe2Si9B14Mn4 alloy was successful prepared with low μe of 3020, low Hc of 1.7 A/m and high resistance to DC bias 6 times that of as-quenched alloy at the DC field of 300 A/m.

Electronic specific heats for amorphous and crystallized alloys

The low temperature specific heats of (Fe0.5Co0.5)72B20Si4Nb4 amorphous and crystallized alloys are measured and analyzed from 1.4 to 110xa0K. Specific heats can be well fitted by electronic and phonon contribution terms. It is found that the electronic contribution term in specific heat for amorphous alloy is larger than that for crystallized one, and this phenomenon has been interpreted in detail. The research shows that the electronic density of states at the Fermi level and the localized loose “rattler” atoms in oversized cage structure may make contributions to the enhancement of electronic specific heat coefficient γ, and result in a larger electronic contribution term. This study is significant for further understanding the structure–property relationship for amorphous alloys at low temperature.

Preparation and magnetic properties of (Co0.6xx

The preparation and soft magnetic properties of (Co0.6Fe0.3Ni0.1)70−x(B0.811Si0.189)25+xNb5 (xxa0=xa00–4) glassy alloys were investigated. This multicomponent system was found to exhibit a distinct glass transition and a wide supercooled liquid region of over 50xa0K before crystallization. As a result, the (Co0.6Fe0.3Ni0.1)70−x(B0.811Si0.189)25+xNb5 bulk glassy alloys with diameters up to 5xa0mm were produced by copper mold casting. In addition to high glass-forming ability, the Co-based glassy alloys also exhibit excellent soft-magnetic properties, i.e., saturation magnetization of 0.54–0.72xa0T, low coercive field of 0.7–1.4xa0A/m, and high effective permeability of 18,600–22,400 at 1xa0kHz under a field of 1xa0A/m. Furthermore, the giant magneto impedance effects of the (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 glassy ribbon at different driving frequencies were also investigated. The results show that the largest impedance ratio is as high as 138xa0% at the frequency of 2.5xa0MHz under an ac current of 0.2xa0mA, together with high field sensitivity of 12.5xa0%/Oe.

Preparation and magnetic properties of (Co 0.6 Fe 0.3 Ni 0.1 ) 70− x (B 0.811 Si 0.189 ) 25+ x Nb 5 bulk glassy alloys

The preparation and soft magnetic properties of (Co0.6Fe0.3Ni0.1)70−x(B0.811Si0.189)25+xNb5 (xxa0=xa00–4) glassy alloys were investigated. This multicomponent system was found to exhibit a distinct glass transition and a wide supercooled liquid region of over 50xa0K before crystallization. As a result, the (Co0.6Fe0.3Ni0.1)70−x(B0.811Si0.189)25+xNb5 bulk glassy alloys with diameters up to 5xa0mm were produced by copper mold casting. In addition to high glass-forming ability, the Co-based glassy alloys also exhibit excellent soft-magnetic properties, i.e., saturation magnetization of 0.54–0.72xa0T, low coercive field of 0.7–1.4xa0A/m, and high effective permeability of 18,600–22,400 at 1xa0kHz under a field of 1xa0A/m. Furthermore, the giant magneto impedance effects of the (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 glassy ribbon at different driving frequencies were also investigated. The results show that the largest impedance ratio is as high as 138xa0% at the frequency of 2.5xa0MHz under an ac current of 0.2xa0mA, together with high field sensitivity of 12.5xa0%/Oe.