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Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution. Graphic abstract

One of the research directions of this study is to determine the possibility of making precise, thin-walled castings from selected iron alloys. The scope of research work is aimed at determining the applicability of the casting process of selected iron alloys with the technology of wax pattern, for making precise castings with a wall thickness of less than 3 mm. The article presents the results of tests carried out for experimental castings with the shape of steps, characterized by different wall thicknesses: 1 mm, 5 mm, 10 mm, 25 mm. The castings were made of LH14, Gs42crMo4, L35H7MP2, LH26N9, 316L cast steel, and a new alloy marked “0”. The metal was smelted in an induction furnace with a capacity of 150 kg. The technology of ceramic shell mould used in the plant was used to make the experimental castings. Ceramic shell moulds were heated in a chamber furnace at a fixed temperature. The time of annealing the ceramic mould was constant in a ceramic form. The following parameters were variable during the tests: iron alloy, pouring temperature, and annealing temperature of the ceramic shell mould.

This work concerns microstructure and mechanical properties investigations of aluminum based composite strengthened with the TiC particles being in nanometer size. The composites were fabricated by the casting method combined with in-situ formation of TiC particles. Applying a suitable composition of components and moderators of SHS reaction which occur during casting, it was possible to cast the samples with TiC particles of size of 150 nm and faceted shape. Microstructure investigations using scanning and transmission electron microscopy (SEM and TEM) allowed to identified the distribution of TiC particles and their preferred location in the microstructure of composites. Also the additional precipitates with different size and shape were identified in investigated samples. Significant increase of strength was observed in in-situ cast composites in comparison to Al-1000 alloy mainly due mainly due to coefficient of thermal expansion and elastic modulus mismatch between the reinforcements and the metal matrix, Hall-Pecht relation and also in minority the Orowan effect.

This paper presents electron magnetic resonance (EMR) and vibrating sample magnetometry (VSM) study of Heusler alloy Ni 50 Mn 35.5 In 14.5 ribbons prepared by melt spinning. The temperature dependency of the EMR spectra and magnetization was measured during the cooling and heating process in the 180–330 K and 100–450 K temperature ranges, respectively. Both methods reveal thermal hysteresis (structural phase transition) and metamagnetic character of this material. The morphology and composition were investigated by scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS).

KOBO type extrusion and following cyclic forging in two perpendicular directions at temperatures 150–200 °C were applied to new Mg–9Li–2Al–0.5Sc alloy to study its effect on strength and microstructure evolution. KOBO extrusion of as cast ingot caused significant grain refinement of (α + β) dual phase Mg–9Li–2Al–0.5Sc alloys down to range 1–10 μm for hcp α phase and 1–5 μm for the β phase as resulted from EBSD studies. At that stage ultimate tensile strength UTS of 168 MPa and elongation of 36% were attained. Additional deformation by cyclic forging alternatively from 2 perpendicular directions caused formation of much finer grains of average size of few hundred nm observed using TEM and close to 1 μm applying EBSD technique. Tensile strength increased after that operation above 200 MPa and elongation above 40%, which were the highest observed in the dual phase Mg–Li based alloys. Deformation by cyclic forging induced formation of strong texture with 0001 plane parallel to forging directions. Additional precipitates of size below 1 μm at α/β interfaces or within β phase were identified as hcp AlSc2 phase. Fine particles of hcp α phase were observed after severe plastic deformation SPD within β phase grains, as effect of diffusion assisted deformation. The amount of hcp α phase increased after SPD up to 70% from initial 40%. High density of defects at α/β interfaces on 0001 planes observed in HRTEM mode was responsible for promotion of hcp phase formation during SPD.

The nano-heterostructures of TiO2/SnO2 and TiO2/CuO thin films have been investigated towards NO2 detection. Thin films have been deposited by reactive magnetron sputtering of metallic targets in Ar + O2 atmosphere. The properties of samples have been characterized by means of X-ray diffraction in grazing incidence GIXRD, X-ray reflectivity XRR, scanning electron microscopy SEM, optical methods and X-ray photoelectron spectroscopy XPS. It has been shown the SnO2 and CuO surface is well developed, with uniformly dispersed polycrystalline nanoparticles of TiO2. The addition of TiO2 thin layer increased the response of SnO2 nanostructure towards NO2. A very high resistance change ~4500 has been demonstrated for TiO2/SnO2 at 150 °C for 4 ppm of NO2, while for the SnO2 sensor the resistance change has been ~2300. The TiO2/SnO2 sensor responses to CO and H2 reducing gases were significantly lower. Such extremely good sensing properties of the n-n heterostructure to NO2 may be assigned to the formed interfaces and higher surface-to-volume ratio. However, TiO2/CuO n-p heterostructures reveal much smaller responses to NO2, what may be attributed to the effect of charge compensation.

Martensitic transformation and magnetic properties in directionally solidified Ni45−xCoxCu5Mn39Sn11 (x = 0, 1, 2) alloys were studied. The martensitic transformation temperature decreases with increasing Co concentration, whereas the Curie temperature of austenite increases, what then alters the magnetic state of austenite at the onset of martensitic phase transformation. Concomitantly the effective magnetic moment of austenite increases by 0.7 μ B / f . u . with Co substitution. Under an applied magnetic field of 5 T the peak values of the magnetic entropy changes reach 11.4 J/kgK (x = 1) and 4.5 J/kgK (x = 2). The variations in magnetic entropy are discussed in relation to a stronger ferromagnetic contribution promoted by Co in the martensite phase.

We report observation of non-conventional twins (i.e. twins with neither the twinning plane being a lattice plane, nor the twinning direction being a lattice vector) in five-layer modulated martensite of the Ni-Mn-Ga ferromagnetic shape memory alloy. The twins were observed using scanning and transmission electron microscopy, and identified by calculations using the mathematical theory of martensitic microstructures.

Ni-Mn-Ga-Co-Cu melt spun ribbons were investigated in the as-cast and annealed states. The initial microstructure of the ribbons was highly anisotropic along the growing direction and was characterized by three different regions of equiaxed, columnar and dendritic grains. At ambient temperature, the microstructure was composed of two martensitic phases, i.e. non-modulated and seven-layer modulated, and the high temperature L21 austenite phase. The stabilization of the austenite phase was a consequence of a strong grain size reduction, especially close to the “contact” side of the ribbons. Subsequent annealing at 823 K triggered atomic ordering, which promoted an improvement in the magnetization. Additional annealing at 1173 K brought about a substantial refinement of the microstructure. The ribbon structure changed to a single non-modulated martensite phase, whereas on a microstructural level, the grains and martensitic plates coarsened considerably. The annealed ribbons resembled oligo-crystalline materials and may cause interest for magnetic field-induced strain applications.

The effect of cobalt addition instead of nickel on the crystal structure, martensitic transformation behaviour and shape memory effect were investigated. Within the analysed range of chemical compo...

Two MgLiAl alloys consisting either of α (hcp) + β (bcc) phases or only β phase were subjected to twist channel angular pressing TCAP (with helical component) or cyclic compression to a total strain of ∊ = 5 in order to study the effectiveness of various deformation modes on grain refinement. After the first TCAP pass grains of α phase were refined from 30 μm down to about 6 μm and of β phase from initial 200 μm down to 8 μm. MAXStrain cycling led to much finer grains of α and β phases in the range 200 – 300 nm causing higher hardening and indicating higher effectiveness of the process. The Li2MgAl precipitates were refined during severe plastic deformation (SPD) processes and in addition fine particles of hexagonal α phase of size below 100 nm were observed within the β phase showing orientation relationship (0001) α ‖ (011) β. Two-phase material after SPD showed deviation of about 1.5° from the ideal Burgers orientation relationship (0001) α ‖ (011) β.

In order to obtain optimal mechanical properties, the effect of heat treatment on the precipitation hardening in multicomponent Fe-based shape memory alloys (containing Ni, Co, Al, Ta, B) was studied. The polycrystalline material was investigated after application of three different processing schemas: slowly cooled, quenched and subsequently annealed with various aging conditions. The study was carried out using synchrotron X-ray diffraction along with mechanical tests, revealing the evolution of strengthening phases. As a result an optimum heat treatment for 10 h at 700°C was established yielding an optimal mechanical response.

This work presents the results concerning microstructural, mechanical property and electrical resistance investigations of La1- x Sr x CoO3 thin films produced by the laser ablation (PLD – Pulsed Laser Deposition) method on Si and MgO single crystal substrates with (001) orientation. The microstructure and chemical/phase composition analysis of the deposited films was carried out using scanning/transmission electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, adhesion and nanohardness tests were performed. The investigations allowed verification of the quality of the prepared La1- x Sr x CoO3 thin films and show that implementing the PLD technique makes it possible to obtain smooth and dense films with nanocrystalline structures, while preserving the composition of the bulk target. Research studies showed that by properly selecting the parameters for the PLD process it is possible to deposit films with a significantly lower amount and smaller size of undesirable nanoparticles. A specialized measuring station was used to determine the response of thin films to an oxidizing gas atmosphere. The observed decrease in resistance of the thin films in the presence of 50 ppm of NO2 oxidizing gas is typical for p-type semiconductors. This indicates that all of the produced films exhibit a sensitivity to this gas and could be used as NO2 sensors.

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe72−xNi8Nb4CuxSi2B14 alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔGamorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔGmix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures Tx1onset and Tx1 of the alpha-iron phase together with the activation energy Ea for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 104 Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).

Multilayers consisting of graphene oxide (GO) and α-Fe2O3 thin layers were deposited on the ceramic substrates by the spray LbL (layer by layer) coating technique. Graphene oxide was prepared from graphite using the modified Hummers method. Obtained GO flakes reached up to 6 nanometers in thickness and 10 micrometers in lateral size. Iron oxide Fe2O3 was obtained by the wet chemical method from FeCl3 and NH4OH solution. Manufactured samples were deposited as 3 LbL (GO and Fe2O3 layers deposited sequentially) and 6 LbL structures with GO as a bottom layer. Electrical measurements show the decrease of multilayer resistance after the introduction of the oxidizing NO2 gas to the ambient air atmosphere. The concentration of NO2 was changed from 1 ppm to 20 ppm. The samples changed their resistance even at temperatures close to room temperature, however, the sensitivity increased with temperature. Fe2O3 is known as an n-type semiconductor, but the rGO/Fe2O3 hybrid structure behaved similarly to rGO, which is p-type. Both chemisorbed O2 and NO2 act as electron traps decreasing the concentration of electrons and increasing the effective multilayer conductivity. An explanation of the observed variations of multilayer structure resistance also the possibility of heterojunctions formation was taken into account.

The specific combinations of materials and dopants presented in this work have not been previously described. The main goal of the presented work was to prepare and compare the different properties of newly developed composite materials manufactured by sintering. The synthetic- (SHAP) or natural- (NHAP) hydroxyapatite serves as a matrix and was doped with: (i) organic: multiwalled carbon nanotubes (MWCNT), fullerenes C60, (ii) inorganic: Cu nanowires. Research undertaken was aimed at seeking novel candidates for bone replacement biomaterials based on hydroxyapatite—the main inorganic component of bone, because bone reconstructive surgery is currently mostly carried out with the use of autografts; titanium or other non-hydroxyapatite -based materials. The physicomechanical properties of the developed biomaterials were tested by Scanning Electron Microscopy (SEM), Dielectric Spectroscopy (BSD), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC), as well as microhardness using Vickers method. The results showed that despite obtaining porous sinters. The highest microhardness was achieved for composite materials based on NHAP. Based on NMR spectroscopy, residue organic substances could be observed in NHAP composites, probably due to the organic structures that make up the tooth. Microbiology investigations showed that the selected samples exhibit bacteriostatic properties against Gram-positive reference bacterial strain S. epidermidis (ATCC 12228); however, the property was much less pronounced against Gram-negative reference strain E. coli (ATCC 25922). Both NHAP and SHAP, as well as their doped derivates, displayed in good general compatibility, with the exception of Cu-nanowire doped derivates.

The quaternary Mg–9Li–2Al–0.5Sc alloy (in wt%) was prepared from pure components. After homogenization, the alloy was subjected to severe plastic deformation by KoBo extrusion and cyclic forging leading to grain refinement in the range of 0.5–2 µm of hexagonal close-packed (HCP) α phase. Deformed alloys showed high ultimate tensile strength near 200 MPa and good elongation in the range 30–40% at room temperature (RT). Large elongations close to 200% were obtained during the tensile test at a temperature of 200 °C. Deformed samples showed the presence of multiple voids confirming grain boundary sliding mechanism of deformation. Twins on {10$$\overline{1}$$ 1 ¯ 2} planes were identified using electron backscatter diffraction analysis, being in a good agreement with the earlier observation of Mg–Li and Mg–Sc alloys. Intermetallic phases such as cubic MgSc were identified in deformed alloys mostly within HCP α phase, whereas HCP MgSc2 particles were observed within body-centered cubic (BCC) β phase. Intermetallic phases were responsible for RT strengthening of alloys and slightly lower tensile elongation during superplastic deformation. Formation of the HCP α phase was observed within the BCC β phase in tensile deformed alloys. Atomic-level nucleation of HCP phase within the β phase was identified by the use of high-resolution transmission electron microscopy technique.

Thin-film n-n nanoheterostructures of SnO2/TiO2, highly sensitive to NO2, were obtained in a two-step process: (i) magnetron sputtering, MS followed by (ii) Langmuir-Blodgett, L–B, technique. Thick (200 nm) SnO2 base layers were deposited by MS and subsequently overcoated with a thin and discontinuous TiO2 film by means of L–B. Rutile nanopowder spread over the ethanol/chloroform/water formed a suspension, which was used as a source in L–B method. The morphology, crystallographic and electronic properties of the prepared sensors were studied by scanning electron microscopy, SEM, X-ray diffraction, XRD in glancing incidence geometry, GID, X-ray photoemission spectroscopy, XPS, and uv-vis-nir spectrophotometry, respectively. It was found that amorphous SnO2 films responded to relatively low concentrations of NO2 of about 200 ppb. A change of more than two orders of magnitude in the electrical resistivity upon exposure to NO2 was further enhanced in SnO2/TiO2 n-n nanoheterostructures. The best sensor responses RNO2/R0 were obtained at the lowest operating temperatures of about 120 °C, which is typical for nanomaterials. Response (recovery) times to 400 ppb NO2 were determined as a function of the operating temperature and indicated a significant decrease from 62 (42) s at 123 °C to 12 (19) s at 385 °C A much smaller sensitivity to H2 was observed, which might be advantageous for selective detection of nitrogen oxides. The influence of humidity on the NO2 response was demonstrated to be significantly below 150 °C and systematically decreased upon increase in the operating temperature up to 400 °C.

Transitioning current cooling and refrigeration technologies to solid-state cooling leveraging the magnetocaloric effect would improve efficiency and eliminate a harmful influence on the environment. Employing additive manufacturing as a production method would increase geometrical freedom and allow designed channels and porosity in heat exchangers made from magnetocaloric materials, to increase surface area for heat transfer via a fluid. This study is the first to demonstrate a successful deposition of the Ni43Co7Mn39Sn11 magnetocaloric material by direct laser deposition. Samples were defined as either properly- or overbuilt, and representative ones were characterized for microstructural features before and after homogenization heat treatment, as well as magnetic behavior and constituent phases. As-built microstructures consisted of dendrites, columnar grains, and elongated cells, with a mix of both austenite and 7M martensite phases. Homogenization increased the fraction of 7M martensite, and encouraged distinct equiaxed and columnar grains, eliminating dendrites and cellular structures. The increased fraction of the weak magnetic martensitic phase also resulted in a strong reduction of the saturation magnetization. Some differences in structure and performance may be related to an energy density difference causing higher Mn loss in the properly built sample, with a lower powder-to-energy input ratio. As a whole, it is found that direct laser deposition (DLD) additive manufacturing of Ni-Mn-based magnetocaloric material is very promising, since representative transformation, phase state, and magnetic properties have been achieved in this study.

The dependences of the macro- and microstructures as well as the hardness of local TiC-Fe-type reinforcements (LR) fabricated in situ in steel casting using compacts containing different contents of TiC reactants and the addition of an Fe moderator have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Vickers hardness (HV) tests. Five powder mixtures were selected for compact preparation; one of them contains only TiC reactants, while the other four contain TiC reactants as well as 10, 30, 50, and 70 wt pct Fe moderator additions, respectively. Next, the ready compacts were introduced to the mold cavity and poured by cast steel for the in situ LR fabrication. This is the first time, through this study, that the fragmentation phenomena was revealed by macrostructural observations of the LR produced with only the TiC reactants. The increasing Fe content gradually limited the fragmentation and infiltration processes and stabilized the dimensions of the LR. With the increasing contents of the Fe moderator, the refinement of the TiC particles in the LR was observed. Due to the limited infiltration process and high surface content of the TiC, the LR produced with 30 wt pct Fe exhibited the greatest hardness.

Ordering effects in the Ni49Co1Mn37.5Sn6.5In6 alloy were studied by subjecting the alloy to annealing at 1220 K followed by water quenching and to subsequent annealing at 1070 K followed by slow cooling. Martensitic transformation temperature increases by 10 K owing to the slow cooling process, which further invites a change in the martensite structure: 6M → 10M. Across the transformation, regardless of the heat treatment applied, austenite phase is paramagnetic and it transforms into a weakly magnetic martensite. Magnetic moment of martensite is boosted due to slow cooling ( $$ \Delta \mu_{\text{eff}}^{\text{M}} = 1 \mu_{\text{B}} $$ ). Observed behaviours are associated with the changes in the degree of atomic ordering. Irrespective of the magnetic state of martensite, ordering process mitigates the transformation temperature most likely through the interaction with the free energy difference and through the influence of antiphase domains on the twinning stress.

Magnetic properties and exchange bias of $$\hbox { Ni}_{45}\hbox {Co}_{5}\hbox {Mn}_{35.5}\hbox {In}_{14.5}$$ ribbons were investigated by vibrating sample magnetometry (VSM) and electron magnetic resonance (EMR). Curie temperatures determined by using VSM and EMR methods are equal to 374 K and 377 K, respectively. Additionally, the EMR measurements revealed the existence of a weak ferromagnetic resonance (FMR) line in the paramagnetic region. The upward deviation of the integral intensity from Curie–Weis low below temperature $$T^*$$ and above $$T_\mathrm{C}$$ confirms the existence of ferromagnetic phase in this temperature region. Below $$T_\mathrm{C},$$ the integral intensity does not saturate, which can suggest the coexistence of different magnetic phases at low temperature range. Additional confirmation on the coexistence of magnetic phases in the sample are asymmetric hysteresis loops associated with the spontaneous exchange bias effect. The dependence of EMR signal on cyclic repetition of measurement is also discussed.

In the presented work, a systematic study of crystal structure, microstructure, magneto-structural behavior and inverse magnetocaloric effect in the Ni44Co6Mn39Sn11-xSix (x = 1, 2 at.%) Heusler alloys, obtained by conventional casting and rapid solidification process, have been performed. All alloys, independently of the chemical composition, i.e. different addition of Si and fabrication process (melt-spinning and induction melting) were fully martensitic at ambient temperature. This was the case in spite of the large difference in the mean grain size of ribbons compared to bulk. Interestingly, the microstructure of ribbons consists of larger grains of about 5–20 μm in diameter with martensitic relief and smaller cells of about 1 μm. The crystal structure of both ribbons and bulk was identified as modulated six-layered (12 M) martensite with five additional spots between main reflections in the reciprocal space. The characteristic temperatures of the martensitic transformation were lower for melt-spun ribbons with respect to bulk. This may be connected with the grain refinement, internal stresses and high density of dislocations caused by rapid solidification process. Moreover, the addition of Si enhances the transformation temperatures. The calculated values of magnetic entropy change were higher for bulk alloys than ribbons.

The technology of structure refinement in materials with the aim of achieving substantial mechanical properties and maintaining the required plasticity level is becoming increasingly useful in industrial practice. Magnesium alloys are very progressive materials for utilization in practice thanks to their high strength-to-weight ratios (tensile strength/density). The presented paper analyses the effect of the input heat treatment of the AZ31 alloy on the change of structure and strength properties through the process of severe plastic deformation (SPD), which finds an increasing utilization, especially in the automotive and aviation industry. For the study of the influence of the SPD process (ECAP method) on the properties of the AZ31 alloy, two types of thermal treatment of the initial state of the structure were selected. The analysis of the structure of the AZ31 alloy was performed in the initial state without heat treatment and subsequently after heat treatment. In the next part, the influence of the number of passes on the strengthening curves was evaluated. Mechanical properties of the AZ31 alloy after ECAP were evaluated by hardness measurement and completed by structure analysis.

3Y-ZrO2-Ti composites obtained by slip casting method were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the ...

The precipitation hardened AA 6013 aluminium alloy was extruded by means of the KoBo extrusion method with an oscillating die. In the presented paper, the influence of two different die rotation frequencies on the microstructure and mechanical properties after KoBo deformation and during post-deformation ageing process is discussed. Initial materials were conventionally hot extruded rods. The extrudates were heat treated to T6 condition and subsequently deformed using the KoBo method, at two frequencies: 2.5 and 8 Hz. The obtained samples were characterised by static tensile tests, scanning and transmission electron microscopy (SEM and TEM), and differential scanning calorimetry (DSC). Electron back scattered diffraction (EBSD) in SEM was applied in order to verify grain size, density of boundaries and local texture. TEM and DSC were used to analyse the influence of plastic deformation on the precipitation process. The results revealed that die oscillation frequency has a great influence on the behaviour of materials during ageing.

This work describes the production of nanocrystalline TiO2 and SnO2 oxides, as well as their nanocomposites (containing 26.9, 58.7 and 79.0wt.% of SnO2) with two-stage sol-gel method combined with high temperature treatment. The phase composition and medium size crystallites were determined using X-ray diffraction analysis (XRD) and revealed that the nanocomposites crystallize in tetragonal structures of TiO2 - anatase and SnO2 - cassiterite. Specific surface area of the nanopowders, measured using sorption method (BET), changed from 42.1 to 160.8m2/g. The morphology of the nanopowders was observed using transmission electron microscope (TEM). As indicated by TEM images, the manufactured nanopowders were well crystallized and consisted of small, spherical grains. The obtained nanopowders were also tested for NH3 gas detection application. The presented method of nanopowders synthesis enables to obtain nanocrystalline TiO2 and SnO2 oxides, as well as composites from TiO2-SnO2 of known and controlled chemical and phase composition. It also enables to obtain composites used for gas sensors. The sensor made of composite containing 58.7wt.% of SnO2 exhibited the best NH3 sensing features.

In this paper, the electron magnetic resonance (EMR) of Ni 47 Co 3 Mn 35.5 In 14.5 alloy in ribbon and powder form are investigated. The EMR spectra for ribbons were registered within the temperature ranges 4 K ⩽ T ⩽ 100 K and 140 K ⩽ T ⩽ 380 K and for powdered ribbon within the temperature range 140 K ⩽ T ⩽ 380 K. Additionally, the magnetic properties of ribbon were also studied by using vibrating sample magnetometer (VSM) in the temperature range of 85 K ⩽ T ⩽ 400 K. At high temperature, the EMR signal consist of a single, asymmetric line. The temperature dependence of the inverse integrated intensity exhibits a Curie–Weiss like behaviour and Curie temperature ( T C ) determined from VSM equals 333 K. Below T C for ribbon sample the low field microwave absorption (LFMA) line was observed. The EMR spectra recorded for the powder sample are of a different shape than those for the ribbon sample. The powdering causes an increase of the effective skin depth, and the high-temperature lines lose asymmetric character. The Curie temperature is shifted relative to Curie temperature determined for the ribbon sample, but the structural phase transition is preserved.

In the present work, we investigated in detail the thermal/crystallization behavior and magnetic properties of materials with Fe84.5-xCoxNb5B8.5P2 (x = 0, 5, 10, 15 and 20 at.%) composition. The amorphous ribbons were manufactured on a semi-industrial scale by the melt-spinning technique. The subsequent nanocrystallization processes were carried out under different conditions (with/without magnetic field). The comprehensive studies have been carried out using differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, hysteresis loop analyses, vibrating sample magnetometry and Mössbauer spectroscopy. Moreover, the frequency (up to 300 kHz) dependence of power losses and permeability at a magnetic induction up to 0.9 T was investigated. On the basis of some of the results obtained, we calculated the values of the activation energies and the induced magnetic anisotropies. The X-ray diffraction results confirm the surface crystallization effect previously observed for phosphorous-containing alloys. The in situ microscopic observations of crystallization describe this process in detail in accordance with the calorimetry results. Furthermore, the effect of Co content on the phase composition and the influence of annealing in an external magnetic field on magnetic properties, including the orientation of the magnetic spins, have been studied using various magnetic techniques. Finally, nanocrystalline Fe64.5Co20Nb5B8.5P2 cores were prepared after transverse thermo-magnetic heat treatment and installed in industrially available portable heating equipment.

M2 tool steel was used as a feedstock material for casting from the the semisolid range between 1310-1350 o C corresponding to 25 - 50 % of the liquid phase. The chemical composition of the investigated steel is following: 0.85%C, 3.9 %Cr, 6.7 %W, 4.7 %Mo and 1.7 % V. A specially constructed machine allowed thixoforming in a protective argon atmosphere and semisolid forming at a high piston velocity powered by a high air pressure. After heating of the feedstock using induction heating by the stamping of semi-liquid sample to a graphite mould pre-heated by resistance heating. The material after thixoforming from 1315 o C shows a globular microstructure with a relatively small globule’s size between 30-50 μm. The crystal structure of globules contained, austenite and martensite, while that of the eutectic, ferrite and W 2 C, Fe 3 C, Mo 2 C, M 23 C 6 and VC carbides as determined by X-ray studies and confirmed using electron diffraction studies. The alloying elements like Mo, W and V are concentrated in the eutectic, while Cr only in thixoformed samples segregates to the carbides and indeed M 23 C 6 was identified. The hardness significantly increases up to 780 HV after thixo-forming due to formation of martensite. The other part was cast from the liquid phase at 1450 o C using melt spinning method allowing high cooling rate. The microstructure of melt spun ribbon shows a cellular microstructure of austenitic and martensitic structure without the eutectic. The WC and M 23 C 6 carbides were located at the cell’s boundariers. The microhardness near 1300 HV of the ribbon was much higher than that of semisolid formed samples.

Structural, magnetic and mechanical properties of Ni50Mn37.5Sn12.5-xInx (x = 0, 2, 4, 6% at.) alloys sintered by vacuum hot pressing were investigated. The porosity of sintered alloys increases with increasing of In concentration. The addition of In leads T C A to decrease while Ms is shifted to higher temperatures. Annealing sintered samples at 1020 K for 24 h allowed for lowering of the thermal hysteresis and narrows the temperature range of the forward and reverse martensitic transformations. Ternary Ni–Mn–Sn alloy exhibits the best mechanical properties and it can be plastically deformed up to about 5% while maintaining about 2000 MPa strength. TEM observations revealed unique microstructure observed in the case of polycrystalline Heusler alloys consisting of equiaxed grains of martensite and austenite with size of about 2 μm.

Electron microscopy techniques were used to characterize the microstructure and deformation behavior of AZ61 alloy proceeded by ECAP. The commercial AZ61 alloy subjected to severe plastic deformation possesses a two-phase microstructure consisting of solid solution matrix and massive γ-phase Mg17Al12, or Mg17(Al,Zn)12 distributed mostly at grain boundaries. Based on selected area diffraction and electron back scattered diffraction applied to a sample after the third pass, it can be concluded that plastic deformation induced by ECAP occurs mainly by slip mode forming a high density network of dislocation inside the grains. The grains size was significantly refined to 1.4 μm after the third pass of ECAP. The refinement of grain size is probably due to polygonization process associated with formation of high angle grain boundaries due to dislocations rearrangement. (Al, Zn)12Mg17 precipitates of size scattered from 100 to 200 nm and also the primary precipitates of Al6Mn phase were observed in this alloy.

Ga&ndash, Sn&ndash, Zn eutectic alloy is a non-toxic liquid metal alloy which could be used in a multitude of applications, including as a heat transfer agent, in gas sensing, and in medicine. Alloys containing gallium readily oxidise in air, forming a thin oxide layer that influences the properties of liquid metals and which has not been studied. In this study, the oxide layer formed on Ga&ndash, Zn alloy was transferred at room temperature onto three substrates&mdash, quartz, glass and silicon. The contact angle between the liquid alloy and different substrates was determined. The obtained thin oxide films were characterised using atomic force microscopy, X-ray photon spectroscopy, and optical and transmission electron microscopy. The contact angle does not influence the deposition of the layers. It was determined that it is possible to obtain nanometric oxide layers of a few micrometres in size. The chemical composition was determined by XPS and EDS independently, and showed that the oxide layer contains about 90 atom % of gallium with some additions of tin and zinc. The oxides obtained from the eutectic Ga&ndash, Zn liquid alloys appear to be nanocrystalline.

Selective Laser Melting was successfully used as a fabrication method to produce Ni-Mn-Ga and Ni-Mn-Ga-Fe ferromagnetic shape memory alloys. The starting material in a powder form with an average particle size of about 17.6 µm was produced by milling of as melt-spun ribbons. The microstructure, phase composition, and martensitic transformation behavior of both powder precursors and laser melted alloys were investigated by several methods, including high energy X-ray diffraction, electron microscopy, and vibrating sample magnetometry. The as laser melted materials are chemically homogenous and show a typical layered microstructure. Both alloy compositions have a duplex structure consisting either of austenite and 10M martensite (Ni-Mn-Ga) or a mixture of 14M and NM martensitic phases (Ni-Mn-Ga-Fe), contrary to the as milled powder precursors showing fcc structure in both cases. The forward martensitic transformation takes place at 336 and 325 K for Ni-Mn-Ga and Ni-Mn-Ga-Fe, respectively, while the magnetic response is much stronger for Ni-Mn-Ga than for the quaternary alloy. The results show that Selective Laser Melting allows for producing of good quality, homogenous materials. However, their microstructural features and consequently shape memory behavior should be tailored by additional heat treatment.

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe72−xNi8Nb4CuxSi2B14 alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔGamorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔGmix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures Tx1onset and Tx1 of the alpha-iron phase together with the activation energy Ea for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 104 Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).

Materials and design 197, 109225 (2021). doi:10.1016/j.matdes.2020.109225, The study focuses on the superelastic effect in single-crystalline boron-doped Fe-based shape memory alloys. Thehomogenized and quenched single crystals were subjected to a heat treatment at 973 K for variable aging times.As a result, small and coherent nanometer-sized $γ′$ (Ni$_3$Al-type) precipitateswere formed. Itwas established thatFe-28Ni-17Co-11.5Al-2.5Ta-0.05B single crystals oriented along [001] direction exhibit the fully reversiblesuperelastic behavior up to 14.3% compression strain at 77 K reaching the maximum theoretical value. Theboron addition suppressed completely the formation of the brittle $β$ phase and reduced the average precipitatesize of the $γ′$ precipitates. Using high-energy synchrotron radiation and high-resolution transmission electronmicroscopy analysis the volume fraction and precipitate size of $γ′$ were determined indicating that both factorsare critical in obtaining the largest superelastic reversibility. Boron addition counters the initial effect of mechanicalstabilization which was detected in single crystals without boron. Unlike the thermally induced martensitictransformation, applied stresses produce a different austenite/martensite interface composed of interchangingaustenite and martensite variants. It is also demonstrated that upon loading/unloading cycles the moving transformationfront divides the material into three district regions i.e. single variant of austenite, austenite intermixedwith martensite and single variant of martensite., Published by Elsevier Science, Amsterdam [u.a.]

Heusler-type Ni–Mn–Sn magnetic shape memory alloys (MSMAs) that exhibit a significant magnetocaloric effect due to magnetic field-induced martensitic transformation (MT) represent promising applications within the field of solid-state cooling. However, their MT and physical properties strongly depend on the intricacies of the fabrication technology employed. In the current study, we demonstrated the advantages of the use of powder metallurgy in the preparation of MSMAs. Powders were vacuum hot pressed to fabricate Ni44.0Mn43.5Sn12.5-xAlx (x = 1, 2, 3 at.%) MSMAs. The way in which the Al influenced the martensitic transformation (MT) behavior, the structural characteristics, and the thermomechanical properties of the MSMAs was investigated. The findings revealed that the MT temperature increases significantly in response to Al doping, by approximately 20 K/1 at.%Al. Striking nanostructural states were revealed in the austenite phase, giving rise to the unusual stress-strain behavior of the alloys studied.

The structural and magnetic properties of Ni 50 Mn 37.5 Sn 12.5 single crystal were investigated. The alloy undergoes martensitic transformation at 308 K from the austenite phase to the structurally modulated tetragonal 4M martensite phase with lattice parameters a 4M = 6.177 A, c 4M = 5.669 A. The alloy shows 7.9% pre-strain upon uniaxial compression along the 〈001〉 direction, which is near the theoretical 8.2% maximum twinning strain. Magnetization measurements reveal that the magnetic anisotropy of the martensite phase is uniaxial with the easy magnetization axis corresponding to the shortest c axis of the tetragonally distorted unit cell, while its a axis is the hard magnetization direction. The magnetic anisotropy constant K u saturates at low temperature around 7 × 10 4 J/m 3 and then gradually decreases with increasing temperature as the system approaches the Curie temperature of martensite at 215 K.