•ε-Fe80Mn20 HCP phase the first product of primary crystallization in Fe-(Co)-Mn-Mo-B alloys.•α-Fe phase appears only in alloys containing Co.•The higher TC the larger the peak value of ...magnetocaloric effect in Fe-(Co)-Mn-Mo-B alloys.
Microstructure, revealed by X-ray diffraction and transmission Mössbauer spectroscopy, and some thermomagnetic properties of the amorphous Fe70-xCoxMn10Mo5B15 (x = 0, 0.25 and 0.5) alloys in the as-quenched state and after accumulative annealing at Ta1=723K, Ta2=753K, Ta3=853K and Ta4=903K for 0.5 h have been studied. After the annealing at Ta1 and then at Ta2 the ribbons remain in the amorphous state, whereas after the final heat treatments at Ta3 and Ta4 they are partially crystallized. The grains of the hexagonal ε-Fe80Mn20 phase, 8 nm and 12 nm in size after the annealing at Ta3 and Ta4 for x = 0 and 0.5, respectively, are paramagnetic at room temperature and the first product of crystallization. After the final annealing at Ta4 in samples containing Co (x = 0.25 and x = 0.5) α-Fe grains are also detected. X-ray diffraction studies are qualitatively very consistent with transmission Mössbauer spectra measurements. The Curie temperature (TC) for x = 0 decreases after the annealing at Ta1 in comparison with the as-quenched state and then increases after the heat treatment at Ta2, whereas in the alloys containing Co atoms (x = 0.25 and 0.5) only the increase of TC on annealing at Ta1 and at Ta2 is observed as compared to the as-quenched state. Isothermal magnetic entropy change is rather modest and reaches its peak value in the vicinity of the Curie temperature of the amorphous phase. The higher TC the larger peak value of the magnetic entropy change. An attempt to elucidate such behavior is undertaken.
•Ti fully dissolves in NiMnGa-based single phase structure.•Gd addition promotes dual-phase microstructure in the NiMnGa-based alloy.•Ti for Ga substitution leads to the decrease of the martensitic ...transition temperature.•Gd shifts the martensitic transition temperature to the room temperature regime.•Ti and Gd improved the mechanical properties of the NiMnGa-based alloy.
The present study is focused on the influence of Ti and Gd doping at the Ga site on the microstructure, magnetic and mechanical properties of the polycrystalline Ni50Mn25Ga20-xZx (x = 0 or 5, Z = Gd, Ti) magnetic shape memory alloys. Microstructure investigations show that reference Ni50Mn25Ga25 and Ti-doped alloys, both in the as-cast and annealed state, are single phase materials, whereas Gd-doped sample reveals dendritic dual-phase structure with substantial distinction between Gd-rich and Gd-poor regions. Thermomagnetic measurements expose reversible martensitic transition in the Ni50Mn25Ga25 and Ni50Mn25Ga20Ti5 alloys, where Ti addition to NiMnGa composition leads to the decrease of phase transformation temperature from TM = 193 K for reference sample to TM = 172.5 K for Ti-doped material. Furthermore, the Ni50Mn25Ga20Gd5 alloy does not experience fully martensitic transition. Temperatures of magnetic transformation also varies with chemical composition and equals to 379 K, 318 K and 370 K for the annealed Ni50Mn25Ga25, Ni50Mn25Ga20Ti5 and Ni50Mn25Ga20Gd5 alloy, respectively. Mechanical properties investigation based on the nanoindentation measurements shows beneficial influence of doping elements on material hardness. In addition, planar distributions of hardness allow to deconvolute mechanical properties of each individual phase of the Ni50Mn25Ga20Gd5 alloy.
Microstructure, Curie temperature and isothermal magnetic entropy change of the amorphous Fe70Mn10Mo5B15 alloy in the as-quenched state and after annealing within the amorphous state at Ta1=723K and ...after the accumulative annealing at Ta1=723K and then at Ta2=753K for 0.5 h have been studied. The transmission Mössbauer spectra recorded at 300K are typical of a paramagnetic amorphous alloy and do not reveal distinct changes on annealing. The spectra in all cases are decomposed into a set of symmetric quadrupole doublets ascribed to the amorphous phase and a single line stemming from medium range ordered (MRO) regions which are paramagnetic at room temperature. The volume fraction of such MRO regions is small and increases only slightly on annealing. The Curie temperature of the amorphous phase decreases from 298 K in the as-quenched state to 268 K after the annealing at Ta1 and then increases to 282 K after the accumulative heat treatment at Ta1 and Ta2 due to invar effect. The isothermal magnetic entropy change of the alloy exhibits the “caret like” behavior with the peak values near the Curie points of the amorphous phase. The composites consisted of two adherent ribbons with different mass fraction (α) subjected to the annealing and made of two ribbons in the as-quenched state and after the heat treatment at Ta1 show the flat maxima of the magnetic entropy change in the temperature spans 14K and 34K for α=0.7 and α=0.5 in the former and latter composite, respectively. Parameter α denotes the mass fraction of the ribbon annealed at Ta1 in the composites. The flat maximum of the magnetic entropy change is obtained for the composite made of two ribbons with the same chemical composition but different thermal history. The refrigerant capacity (RC) of the amorphous Fe70Mn10Mo5B15 alloy is about 115 J/kg in the as-quenched state and decreases slightly on annealing. RC is enhanced for the composites in comparison with their components.
•Amorphous Fe70Mn10Mo5B15 alloy paramagnetic at room temperature.•Its Curie point TC = 298 K.•TC decreases and then increases on annealing within amorphous state.•Flat maximum of magnetic entropy change in composite.•The composite consist of the ribbon with different thermal history.
The paper presents the preliminary results of research on determining the possibilities of using available on the market commercial gypsum kinds as a binder for foundry moulding and core sandmixes. ...Construction gypsum and plaster gypsum, finishing coat and jewelry casting gypsum were tested. Elemental composition of gypsum kinds were carried out using a scanning electron microscope (SEM) with EDS/EDX probe, their crystal structure and phase composition was determined by analyzing the results of X-ray diffraction measurements (XRD) and thermogravimetric studies (TG-DTA). Evaluation of the mechanical properties of selected materials was carried out at the tensile strength test of the dog-bone samples after initial hardening of gypsum mortar at 25 °C for 5 h and drying at 110 °C for 24 hours. The impact of the properties of the used commercial gypsum kinds on the possibility of their use as a valuable binders in the manufacture of the foundry sandmixes for moulds and cores was evaluated. Construction gypsum and finishing coat have the highest tensile strength. Plaster gypsum and finishing coat have the longest setting time. In all tested types of gypsum, the initial water loss during heating occurs at a temperature of about 200 °C. The lowest valuable properties as a binder for sand moulding mixtures has jewelry casting gypsum mass.
Inthe present work the temperature dependence of lattice parameters and magnetic properties of the LaFe11.14−xCo0.66NixSi1.2 (where x=0.1,0.2,0.3) alloys were investigated. X-ray diffraction studies ...of all specimens revealed coexistence of two crystalline phases: the dominant La(Fe, Si)13-type phase and minor fraction of bcc α-Fe. Furthermore changes in negative lattice expansion with the increase of Ni content in the alloy composition were also shown. The increase of Ni content caused rise of the Curie temperature and decrease of the amplitude of magnetic entropy changes.
•We investigated influence of Ni addition on the structure and magnetocaloric effect of the LaFe11.14−xCo0.66NixSi1.2 (where x=0.1, 0.2, 0.3) alloys.•We observed alteration of negative lattice expansion of the La(Fe, Si)13- type phase with increase of Ni addition in alloy composition.•Shift of negative lattice expansion to lower temperatures was studied.
The microstructure and some magnetic properties of the bulk amorphous (Fe 0.61 Co 0.10 Zr 0.025 Hf 0.025 Ti 0.02 W 0.02 B 0.20 ) 100-x Y x (x = 0 or 2) alloys are studied. The as-quenched and ...annealed at 720 K for 15-min alloys, well below the crystallization temperature, as confirmed by X-ray diffraction and Mossbauer spectroscopy studies, are fully amorphous. The investigated alloys are soft magnetic ferromagnets and exhibit relatively high magnetic susceptibility at low magnetic fields. However, the alloys show broad disaccommodation spectra characteristic of amorphous materials. The intensity of disaccommodation distinctly decreases after the addition of 2 at.% of Y to the amorphous Fe 61 Co 10 Zr 2.5 Hf 2.5 Ti 2 W 2 B 20 alloy and also after annealing at 720 K for 15 min. From the analysis of disaccommodation curves, the average activation energies of elementary processes are estimated. The obtained values of the activation energies, equal to about 1.2 eV, and preexponential factor in Arrhenius law in order of 10 - 15 's indicate that observed disaccommodation phenomenon is connected with the ordering of atom pairs near free volumes. In higher magnetic fields, the magnetization fulfils M / M s ~ 1/mu 0 H law, pointing out the presence of quasi-dislocation dipoles with the width lower than the exchange length. After the addition of yttrium to the amorphous Fe 61 Co 10 Zr 2.5 Hf 2.5 Ti 2 W 2 B 20 alloy and the annealing of the samples at 720 K for 15 min, we observe the decrease of the quasi-dislocation dipoles width.
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