Glass formation,magnetic properties and magnetocaloric effect of ternary Ho–Al–Co bulk metallic glass

A ternary Ho–Al–Co system with high glass-forming ability (GFA) was developed and fully glassy rods with diameters up to 1 cm can be produced for the best glass former of Ho₅₅Al_27.5Co_17.5 alloy. The thermal stability and low-temperature magnetic properties of the Ho₅₅Al_27.5Co_17.5 bulk metallic glass (BMG) were studied. The magnetic transition temperature of this alloy is ∼14 K as determined by the thermomagnetic measurement. Two indicators, i.e. isothermal magnetic entropy change (ΔS_M) and the relative cooling power (RCP), were adopted to evaluate the magnetocaloric effect (MCE) of the alloy under a low magnetic field up to 2 T, which can be generated by permanent magnets. The values of |ΔS_M| and RCP are 7.98 J kg⁻¹ K⁻¹ and 191.5 J kg⁻¹, respectively. The Ho₅₅Al_27.5Co_17.5 BMG with good MCE and high GFA provides an attractive candidate for magnetic refrigeration applications, like hydrogen liquefaction and storage.     

Does bulk metallic glass of elemental Zr and Ti exist?

To verify the high-pressure formation of the bulk metallic glass in elemental Zr and Ti, which Zhang and Zhao [Nature (London) 430, 332 (2004)] and Y. Wang et al. [Phys. Rev. Lett. 95, 155501 (2005)] recently reported, the high-pressure states were investigated by our newly developed in situ angle-dispersive x-ray diffraction using a two-dimensional detector and x-ray transparent anvils. Despite the disappearance of all the Bragg peaks in the one-dimensional energy-dispersive data, two-dimensional angle-dispersive data showed several intense Bragg spots even at the conditions where the amorphization was reported. This finding suggests that Zr and Ti do not transform into an amorphous state, but that their grain size becomes large, which causes the missing Bragg peaks in energy-dispersive data.     

Crystallisation behaviour during tensile loading of laser treated Fe–Si–B metallic glass

Effect of tensile loading on crystallisation behaviour of as-cast and laser thermal treated Fe–Si–B metallic glass foils was investigated. Tensile loading lacked any marked influence on the crystallisation behaviour of as-cast and structurally relaxed laser-treated metallic glass foils. Furthermore, the average crystallite/grain size in partially crystallised laser-treated metallic glass foil was nearly equal to the average crystallite/grain size in the region away from the fracture of the same partially crystallised laser-treated metallic glass foil after tensile loading. However, a significant crystallite/grain growth/coarsening of the order of two and half times was observed in the fractured region compared to the region around it for the laser-treated partially crystallised metallic glass foils. The simultaneous effects of stress generation and temperature rise during tensile loading were considered to play a key role in crystallite/grain growth/coarsening.     

Magnetic properties and power losses in Fe–Co-based bulk metallic glasses

Magnetic properties of Fe–Co-based bulk metallic glasses have been experimentally investigated. Samples were prepared by water-cooled Cu-mold injection casting technique. The samples have cylindrical shapes with 0.8 mm diameter and 30 mm length. Amorphous structures were confirmed by the presence of a main halo in X-ray diffraction patterns and by the detection of crystallization signal around 650 °C using differential scanning calorimetry.     

Effect of irradiation on microstructure and hardening of Cr–Fe–Ni–Mn high-entropy alloy and its strengthened version

ABSTRACT

A single-phase fcc high-entropy alloy (HEA) of 20%Cr–40%Fe–20%Mn–20%Ni composition and its strength with yttrium and zirconium oxides version was irradiated with 1.4?MeV Ar ions at room temperature and mid-range doses from 0.1 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive X-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterise the radiation defects and microstructural changes. Nanoindentation was used to measure the ion irradiation effect on hardening. In order to understand the irradiation effects in HEAs and to demonstrate their potential advantages, a comparison was performed with hardening behaviour of 316 austenitic stainless steel irradiated under an identical condition. It was shown that hardness increases with irradiation dose for all the materials studied, but this increase is lower in high-entropy alloys than in stainless steel.     

Investigations on ultrafast welding of glass–glass and glass–silicon

Using ultrafast laser radiation glass substrates are welded with glass and silicon plates. The pump beam is focused by a microscope objective with large NA=0.4 (beam diameter 4 μm) into the glass. After partial absorption of the optical energy, the glass is heated and melted. Procedures for high-quality welding of glass–glass and glass–silicon substrates with high-repetition ultra-fast laser radiation have been derived at the repetition rate 700 kHz. The dependencies of the dimension and geometry of the welding seam on scan velocity, repetition rate and pulse energy have been investigated defining a process window. Adding a noninterferometric technique for quantitative phase detection with the welding setup, the interaction zone of the welding seam for the welding partners glass–glass is detected. A change in refractive index is induced by heating and compression of the glass and has been detected by phase detection up to 2 μs after irradiation with 100 fs time resolution.     

Thermal and magnetic characterisation of (Co0.402Fe0.201Ni0.067B0.227Si0.053Nb0.05)100–xCux bulk metallic glasses

Abstract

In this work, Co-based (Co_0.402Fe_0.201Ni_0.067B_0.227Si_0.053Nb_0.05)_100–xCu_x bulk glassy alloys (BMG) with 2 mm diameters were formed by suction-casting method and effect of Cu in this system’s thermal stability, glass forming ability and magnetic properties were also investigated. The curves of thermal analysis, obtained using differential scanning calorimetry, show that (Co_0.402Fe_0.201Ni_0.067B_0.227Si_0.053Nb_0.05)_100-xCu_x (x = 0–2) has supercooled liquid region (?T_x) of about 45 K, and reduced glass transition temperature (T_g/T_l) lies in the range from 0.663 to 0.678. The saturation magnetisation (J_s) and coercivity (H_c) for as-cast BMG were in the range of 0.46 T–0.65 T and 13 A/m, respectively.     

Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires

Ni_(50)Mn_(25)Ga_(20)Fe_5 ferromagnetic shape memory alloy microwires with diameters of ～ 30–50 μm and grain sizes of ～ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity,and high-density defects in the as-extracted Ni_(50)Mn_(25)Ga_(20)Fe_5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain(1.9%) with a large recovery ratio(96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.     

Measurements of magnetostriction of paramagnetic Fe–Mo–Cu–B metallic glasses

Magnetostriction of amorphous Fe₇₉Mo₈Cu₁B₁₂, (Fe₁₂Co₁)₇₉Mo₈Cu₁B₁₂ and (Fe₉Co₁)₇₉Mo₈Cu₁B₁₂ prepared by planar flow casting was measured using a direct method. The results indicate that magnetostriction in parallel (_λ∥)$({\lambda }_{\parallel })$ and perpendicular (_λ⊥)$({\lambda }_{\perp })$ directions of applied magnetic field is linearly dependent on magnetic field. In order to determine the influences of chemical composition and the conditions of sample preparation the magnetostriction of pure BCC-Fe, Cu and Mo were also measured. Samples containing Co with Curie temperatures slightly above room temperatures were shown to exhibit a hybrid magnetostriction behaviour with both ferromagnetic and paramagnetic features.     

Improvement of microstructure and magnetic properties of Nd–Fe–B alloys by Nb and Co additions

In order to establish the role of niobium on the hydrogenation, disproportionation, desorption and recombination (HDDR) behavior of near-stoichiometric alloys, two alloys: NdI3Fe8OB7 and Nd13Fe78Nb1Co1B7 (at%) were investigated before, during and after the HDDR process. The microstructure of the as-cast Nb-free alloy before employing the HDDR process was found to consist of three phases, the matrix Nd₂Fe₁₄B (φ) phase, Nd-rich phase and a significant amount of free iron; whereas, the microstructure of the Nb-containing alloy consisted of only the first two phases.     

Thermal conductivity of large-grain niobium and its effect on trapped vortices in the temperature range 1.8–5 K

Experimental investigation of the thermal conductivity of large grain and its dependence on the trapped vortices in parallel magnetic field with respect to the temperature gradient \(\nabla T\) was carried out on four large-grain niobium samples from four different ingots. The zero-field thermal conductivity measurements are in good agreement with the measurements based on the theory of Bardeen–Rickayzen–Tewordt (BRT). The change in thermal conductivity with trapped vortices is analysed with the field dependence of the conductivity results of Vinen et al for low inductions and low-temperature situation. Finally, the dependence of thermal conductivity on the applied magnetic field in the vicinity of the upper critical field H _c2 is fitted with the theory of pure type-II superconductor of Houghton and Maki. Initial remnant magnetization in the sample shows a departure from the Houghton–Maki curve whereas the sample with zero trapped flux qualitatively agrees with the theory. A qualitative discussion is presented explaining the reason for such deviation from the theory. It has also been observed that if the sample with the trapped vortices is cycled through T _c, the subsequent measurement of the thermal conductivity coincides with the zero trapped flux results.     

Dislocation climb and low-temperature plasticity of an Al–Pd–Mn quasicrystal

Dislocations and phason faults have been studied by transmission electron microscopy in an Al-Pd-Mn sample deformed at 300°C under a high pressure. All dislocation movements have occurred by climb, in contrast with the usual interpretations of dislocation motion in quasicrystals. Several modes of dissociation and decomposition of dislocations have been observed, allowing for estimations of phason fault and antiphase-boundary energies. Work softening is tentatively explained in terms of a varying chemical stress.     

The influence of pressure on spontaneous magnetization of Fe60Mn20B20 amorphous alloy at temperature range 77.4–300 K

Abstract

Amorphous, ferromagnetic, invar like, Fe₆₀ Mn₂₀ B₂₀ alloy has been investigated. Two kinds of experiments were carried out for this alloy. The first, using high pressure technique, revealed the influence of pressure on B(H) dependencies within the wide range of temperature under pressure of 0.5 GPa. From the magnetization curves obtained during these experiments the decrease of spontaneous magnetization caused by applied pressure 0.5 GPa at temperature -180°C has been calculated at the rate about 7 10^?11T/Pa.

In the second kind of experiments the measurements of volume magnetostriction up to 720 kA/m magnetic field intensity have been done. Volume magnetostriction coefficient at temperature 77.4 K has been determined to be about 2 10^?11 [A/m]^?1.     

Formation and crystallization kinetics of Nd–Fe–B-based bulk amorphous alloy

In order to improve the glass-forming ability (GFA) of Nd–Fe–B ternary alloys to obtain fully amorphous bulk Nd–Fe–B-based alloy, the effects of Mo and Y doping on GFA of the alloys were investigated. It was found that the substitution of Mo for Fe and Y for Nd enhanced the GFA of the Nd–Y–Fe–Mo–B alloys. It was also revealed that the GFA of the samples was optimized by 4 at.% Mo doping and increased with the Y content. The fully amorphous structures were all formed in the Nd $_{6-{x}}$ Y $_{{x}}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ (x $=$ 1–5) alloy rods with 1.5 mm-diameter. After subsequent crystallization, the devitrified Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ alloy rod exhibited a uniform distribution of grains with a coercivity of 364.1 kA/m. The crystallization behavior of Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ BMG was investigated in isothermal situation. The Avrami exponent n determined by JAM plot is lower than 2.5, implying that the crystallization is mainly governed by a growth of particles with decreasing nucleation rate.     

Electromagnetic wave absorbing properties and hyperfine interactions of Fe–Cu–Nb–Si–B nanocomposites

The Fe–Cu–Nb–Si–B alloy nanocomposite containing two ferromagnetic phases(amorphous phase and nanophase phase) is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy(HRTEM) images show the coexistence of these two phases. It is found that Fe–Si nanograins are surrounded by the retained amorphous ferromagnetic phase. M¨ossbauer spectroscopy measurements show that the nanophase is the D03-type Fe–Si phase, which is employed to find the atomic fractions of resonant57 Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe–Cu–Nb–Si–B nanocomposite are measured in the frequency range of 0.5 GHz–10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than-10 dB in a frequency band of 1.93 GHz–3.20 GHz.     

Internal-friction study of the interstitial–substitutional effect on the deformation behaviour of Nb–O,Nb–Ta–O and Nb–Mo–O single crystals

To investigate the interstitial-substitutional interaction in dislocations, the effect of 0 on the temperature, frequency and amplitude dependence of the internal friction Q ^?1 in Nb–O, Nb-20 mol% Ta–O and Nb-20 mol% Mo–O single crystals has been studied (f = 1.55–8.2 Hz) in the temperature range from 298 to 1473 K. In our previous study, Nb–Mo and Nb–Ta single crystals were found to be strengthened by solute O. It was also suggested that the interstitial–substitutional interaction in dislocations contributes to the increase in their critical resolved shear stress (CRSS). In this study, Snoek-type relaxation peaks due to O are observed between 500 and 700 K in all the single crystals. The Snoek peak of Nb-20mol% Mo–O consisting of several peaks is analysed. The activation energy of the Snoek peak in Nb-20mol% Mo–O is higher than that of Nb–O. These results are attributable to the existence of the interstitial–substitutional complexes. The amplitude dependence of Q ^?1 at intermediate and high temperatures decreases as the O content increases. Moreover, the breakaway stress of Nb-20 mol% Mo–O still has a high value at 1200K and does not decrease much even at 1473 K. This suggests that the formation of Mo–O complexes reduces the dislocation mobility at high temperatures. From the results, the effect of the interstitial-substitutional interaction on the CRSS was discussed.     

The effect of Bi content on the thermal stability and crystallization of Se–Te chalcogenide glass

Glass formation and devitrification of intermediate alloys in the Se–Te–Bi system were studied by differential scanning calorimetry. A comparison of various simple quantitative methods to assess the level of stability of the glassy materials in the above-mentioned system is presented. All of these methods are based on characteristic temperatures, such as the glass transition temperature, T _g, the onset temperature of crystallization, T _in, the temperature corresponding to the maximum crystallization rate, T _p, or the melting temperature, T _m. In this work, a kinetic parameter, K _r(T), is added to the stability criteria. The thermal stability of several compositions of Se–Te–Bi was evaluated experimentally and correlated with the activation energies of crystallization by this kinetic criterion and compared with those evaluated by other criteria. All the results confirm that the thermal stability decreases with increasing Bi content in this glassy system. The crystallization results are analysed and the activation energy and mechanism of crystallization characterized.     

Formation and ordering of local magnetic moments in Fe–Al alloys

The density functional theory is used to study the local magnetic moments in Fe–Al alloys depending on concentration (from 29 to 44 at% Al) and the Fe nearest environment. We have found three different solutions for the system: a spin-spiral wave (SSW) which has a minimum energy and two collinear states, a ferromagnetic one and a state with both positive and negative Fe magnetic moments (the Fe atoms with many neighboring Al atoms around them have negative magnetic moments, while the other Fe atoms—positive). Both the SSW and the negative Fe moments agree with the experiments. Magnetization curves taken from the literature are analyzed. The assumption of percolation character of the size distribution of magnetic clusters describes well the experimental superparamagnetic behavior above 150 K.