Glass-forming ability and corrosion resistance of Al88Y8-xFe4+x (x = 0, 1, 2 at.%) alloys

The effect of iron and yttrium additions on glass forming ability and corrosion resistance of Al88Y8-xFe4+x (x = 0, 1, 2 at.%) alloys in the form of ingots and melt-spun ribbons was investigated. The crystalline multiphase structure of ingots and amorphous-crystalline structure of ribbons were examined by a number of analytical techniques including X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy. It was confirmed that the higher Fe additions contributed to formation of amorphous structures. The impact of chemical composition and structure of alloys on their corrosion resistance was characterized by electrochemical tests in 3.5% NaCl solution at 25 ◦C. The identification of the mechanism of chemical reactions taking place during polarization test along with the morphology and internal structure of the surface oxide films generated was performed. It was revealed that the best corrosion resistance was achieved for the Al88Y7Fe5 alloy in the form of ribbon, which exhibited the lowest corrosion current density (jcorr = 0.09 µA/cm2) and the highest polarization resistance (Rp = 96.7 kΩ·cm2)

The effect of cooling rate on the structure and selected properties of AlCoCrFeNiSix (x = 0; 0.25; 0.5; 0.75) high entropy alloys

High entropy alloys with variable silicon content were prepared by two different methods to determine the influence of the cooling rate and chemical composition on the structure and properties of the alloys. First, the structure of the alloys was investigated using X-ray diffractometry and electron microscopy and compared with Mössbauer spectra to obtain a comprehensive description of the atom arrangement. The formation ability of the BCC and B2 phases was confirmed. The magnetic properties were examined using a vibrating sample magnetometer and Mössbauer spectroscopy. The corrosion resistance behavior was stu died by electrochemical testing. Our results show that the saturation magnetization tends to decrease with increasing silicon content and that the lowest coercive force was noted for rapidly cooled plates. The highest corrosion resistance in a 3.5% NaCl solution characterizes the AlCoCrFeNiSi0.75 alloy in the form of plates. For which Ecorr and jcorr was equal to − 0.155 V and 0.17 μA/cm2. The addition of Si led to an increase in the hardness of the ingots and plates. For example, AlCoCrFeNiSi0.75 shows 859 HV for the ingot and 727 HV for the plate

Influence of magnetite nanoparticles shape and spontaneous surface oxidation on the electron transport mechanism

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe3O4 nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 104 S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges

Tuning of the Structure and Magnetocaloric Effect of Mn1−xZrxCoGe Alloys (Where x = 0.03, 0.05, 0.07, and 0.1)

The aim of the present work is to study the influence of a partial substitution of Mn by Zr in MnCoGe alloys. The X-ray diffraction (XRD) studies revealed a coexistence of the orthorhombic TiNiSi-type and hexagonal Ni2In- type phases. The Rietveld analysis showed that the changes in lattice constants and content of recognized phases depended on the Zr addition. The occurrence of structural transformation was detected. This transformation was confirmed by analysis of the temperature dependence of exponent n given in the relation ΔSM = C·(BMAX)n. A decrease of the Curie temperature with an increase of the Zr content in the alloy composition was detected. The magnetic entropy changes were 6.93, 13.42, 3.96, and 2.94 J/(kg K) for Mn0.97Zr0.03CoGe, Mn0.95Zr0.05CoGe, Mn0.93Zr0.07CoGe, and Mn0.9Zr0.1CoGe, respectively. A significant rise in the magnetic entropy change for samples doped by Zr (x = 0.05) was caused by structural transformation

Structure, Magnetocaloric Effect and Critical Behavior of the Fe60Co12Gd4Mo3B21 Amorphous Ribbons

The aim of the paper was to study the structure, magnetic properties and critical behavior of the Fe60Co12Gd4Mo3B21 alloy. The X-ray diffractometry and the Mössbauer spectroscopy studies confirmed amorphous structure. The analysis of temperature evolution of the exponent n (ΔSM = C·(Bmax)n) and the Arrott plots showed the second order phase transition in investigated material. The analysis of critical behavior was carried out in order to reveal the critical exponents and precise TC value. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental results

Determination of Phase Transition and Critical Behavior of the As-Cast GdGeSi-(X) Type Alloys (Where X = Ni, Nd and Pr)

The aim of the paper is to present a study of the magnetocaloric effect and the nature of phase transition in the Gd80Ge15Si5 (S1), Gd75Ge15Si5Ni5 (S2), Gd75Ge15Si5Pr5 (S3) and Gd75Ge15Si5Nd5 (S4) alloys. The magnetic entropy changes determined for studied samples, under external magnetic field ~3T, were 11.91, 12.11, 5.08 and 4.71 J/(kg K) for S1, S2, S3 and S4, respectively. The values of refrigerant capacity (under ~3T) were 164, 140, 160 and 140 J/kg for S1, S2, S3 and S4, respectively. The first order phase transition was detected for samples S1 and S2, while specimens S3 and S4 manifested the second order phase transition at the Curie point (TC). The analysis of temperature evolution of the exponent n (ΔSM = C·(Bmax)n) showed the validity of this method in detecting either the first or the second order phase transition and the structural transition. The analysis of critical behavior was carried out for samples S3 and S4. The critical exponents and precise TC values were calculated. The ascertained critical exponents were used to determine the theoretical value of the exponent n, which corresponded well with experimental result

A Study of Temperature-Dependent Hysteresis Curves for a Magnetocaloric Composite Based on La(Fe, Mn, Si)13-H Type Alloys

In the present paper, the effect of temperature on the shape of magnetic hysteresis loops for a magnetocaloric composite core was studied. The composite core, based on La(Fe, Mn, Si)13-H, was set up using three component disks with different Curie temperatures. The magnetic properties of the components and the outcome composite core were determined using a self-developed measurement setup. For the description of hysteresis loops, the phenomenological T(x) model was used. The presented methodology might be useful for the designers of magnetic active regenerators

The Structure and Magnetocaloric Effect of MnCoGe Alloy Modified by Nb

The aim of this work was to investigate the effect of partial substitution of Mn by Nb on structure and thermomagnetic properties in the (Mn, Nb)-Co-Ge alloy. The master alloys were prepared by arc-melting in an arc furnace with high purity of constituent elements under a low pressure of Ar. The prepared specimens were studied in as-cast state. The X-ray was performed by BRUKER D8 Advance diffractrometer with Cu Kα radiation. The analysis of the XRD pattern revealed coexistence of two orthorhombic phases with different lattice constants. The analysis of the temperature dependence of magnetizaton confirmed the XRD results and showed that produced material manifested two magnetic phase transitions corresponding to detected phases. The values of the Curie temperature were 275 and 325 K. The values of magnetic entropy change ∆SM equaled 3.30 and 2.13 J/(kg K), respectively for recognized phases. Biphase structure of produced material allowed to reach relatively high refigeration capacity 307 J/(kg). Moreover, the analysis of field dependences of magnetic entropy change (∆SM = CBn) allowed to construct temperature dependence of exponent n. The analysis of elaborated n vs. T curve confirmed biphasic structure of produced material

Anomalous behavior of thermal expansion of α-Fe impurities in the La(Fe,Co,Si)13−La(Fe,Co,Si)_{13-} based alloys modified by Mn or selected lanthanides (Ce, Pr, Ho)

The aim of the present work was to study the negative lattice expansion of the La(Fe,Si)13 phase in the LaFe11.2Co0.7Si1.1 alloy modified by Ce, Ho, Pr or Mn. The highest change of lattice constant was observed for sample doped with Ce, which was result of the first order phase transition, previously observed in this alloy. The gradual decrease of relative change of lattice parameter with increase of Mn content was detected. Furthermore, anomalous behavior of temperature dependence of lattice constant for α-Fe phase was also observed. The X-ray diffraction analysis showed that this phenomenom is caused by negative lattice expansion of the La(Fe,Si)13 phase

Entalpy of Mixing, Microstructure, Structural, Thermomagnetic and Mechanical Properties of Binary Gd-Pb Alloys

The aim of the present work is to study the phase composition, microstructure and magnetocaloric effect of binary Gd100−xPbx (where x = 5, 10, 15 and 20) alloys. The XRD and SEM/EDX analysis confirmed a biphasic structure built by Gd(Pb) and Gd5Pb3 phases. The analysis of M vs. T curves showed the evolution of the Curie point of recognized phases. The temperature dependences of magnetic entropy change revealed two maxima corresponding to the recognized phases. The analysis of the exponent n (ΔSMmax = C(Bmax)n) confirmed the multiphase composition of the produced alloys. The same behavior was also observed in investigations of mechanical properties