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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

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.

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 complex structural and magnetic studies of the annealed rapidly quenched Cu-free Fe72Ni8Nb4Si2B14 alloy (metallic ribbons form) are reported here. Based on the calorimetric results, the conventional heat treatment process (with heating rate 10 &deg, C/min and subsequent isothermal annealing for 20 min) for wound toroidal cores has been optimized to obtain the least lossy magnetic properties (for the minimum value of coercivity and magnetic core losses at 50 Hz). For optimal conditions, the complex permeability in the 104&ndash, 108 Hz frequency range together with core power losses obtained from magnetic induction dependence up to the frequency of 400 kHz was successfully measured. The average and local crystal structure was investigated by the use of the X-ray diffraction method and the transmission electron microscopy observations and proved its fully glassy state. Additionally, for the three temperature values, i.e., 310, 340 and 370 &deg, C, the glass relaxation process study in the function of annealing time was carried out to obtain a deeper insight into the soft magnetic properties: magnetic permeability and cut-off frequency. For this type of Cu-free soft magnetic materials, the control of glass relaxation process (time and temperature) is extremely important to obtain proper magnetic properties.

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.

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.

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.

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.

Microstructure, martensitic transformation behavior and magnetic properties of Ni 44− x Fe x Co 6 Mn 39 Sn 11 ( x = 0, 1, 2 at.%) melt spun ribbons have been investigated. The influence of iron addition has been thoroughly studied by means of electron microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that addition of 1 at.% of iron into quaternary Ni–Co–Mn–Sn Heusler alloy drastically decreases the martensitic transformation temperature by more than 100 K. Higher concentration of iron leads to complete suppression of martensitic transition. The structure of samples change from fully martensite (12 M) through mixed austenite-martensite (L2 1 + 10 M) to fully austenite (L2 1 ) with increase of iron content. Addition of 1 at.% of iron leads to enhance magnetization of both austenitic and martensitic phases and also a small increase of Curie temperature occurs. The largest change of magnetic entropy under 15 kOe measured 2.9 and 0.65 J kg −1 K −1 for alloys where x = 0 and 1, respectively.

The combined effect of ball milling and subsequent heat treatment on microstructure, magnetic, magnetocaloric and exchange bias properties of Ni48Mn39.5Sn10.5Al2 ribbons is reported. The annealing treatment results in the increase of the critical martensitic transformation temperature. The magnetic entropy change ΔSM of the order of 7.9 and −2.3 J kg K−1 for the annealed 50–32 µm powder fraction is determined. This is less than in the as melt spun ribbon but appears at a considerably higher temperature. At the same time EB is decreased due to annealing treatment. This decrease is attributed to the strengthened ferromagnetic exchange coupling due heat induced stress and structural relaxation.

The influence of low temperature annealing and high temperature quenching on martensitic transformation, microstructure, magnetic and exchange bias properties of Ni 48 Mn 39.5 Sn 9.5 Al 3 metamagnetic shape memory alloy ribbons have been investigated. It is shown that with increasing thermal treatment temperature the martensitic transformation temperature increases and the exchange bias is reduced. In the case of low temperature annealing this effect is mediated by stress and structural relaxations, whereas in the case of high temperature annealing followed by water quenching this effect is ascribed to the combined influence of grain size enlargement and composition change resulting from metastability of the Ni–Mn–Sn–Al phase at elevated temperatures. Furthermore low temperature thermal treatment leads to the change in the martensite structure from 4O to 10M as is demonstrated by in situ TEM studies. It is demonstrated that low temperature annealing is a preferable method for fine tuning magnetostructural properties of Ni–Mn–Sn–Al ribbons.

The main goal of this work was to examine the effect of aging process on the precipitation behavior including phase morphology, chemical composition and degree of coherence in Fe–28Ni–17Co-11.5Al-2.5Ta single crystals. The nano-sized and coherent γ′ precipitates were used for strengthening process. The particles were investigated with transmission and scanning electron microscopies along with high energy X-ray diffraction. The single crystalline material of [100] (001) orientation was subjected to three different heat treatments: slowly cooled, quenched and then annealed with various aging conditions. Aging at 973 K for short times results in coherent 2-6 nm-sized γ′ precipitates and fully reversible superelastic strains while annealing at 973 K for 5 h and longer times leads to the precipitation of larger γ’ particles formed together with β phase which significantly reduces the transformed martensite volume fraction.

The effect of Al substitution on microstructure, martensitic transformation and magnetocaloric properties in Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2, 3) alloys is reported. At room temperature, depending on Al concentration, the alloys have typical Heusler L21 austenite structure and/or orthorhombic martensite structure with Pmma space group. A secondary Ni-Mn-Al phase also appears already for low Al concentrations (x ≥ 1). On cooling, irrespective of Al substitution, all the samples show ferromagnetic type ordering below 303 K in the austenite phase. The martensitic transition temperature varies with Al content. All the alloys undergo magnetic field-induced reverse martensitic transformation giving rise to an inverse magnetocaloric effect. The largest magnetic entropy change (8.5 J·kg−1·K−1) is observed near 280 K for the Ni48Mn39.5Sn12.5 alloy.

Directionally solidified Ni–Co–Mn–Sn alloy shows a multiphase solidification microstructure relatable primarily to the varying Co–Mn/Sn ratio. Thermal treatment at 1220 K lasting for 72 h encourages chemical homogeneity with average stoichiometry of Ni45.1Co6.2Mn37.2Sn11.5. At room temperature, despite the chemical uniformity, the as-homogenized alloy shows a multiphase microstructure with coexisting L21 austenite and 6M and 4O martensite phases. The martensite phase preferentially locates at grain boundaries. The onset of the martensitic transition temperature is estimated at 402 K, which overlaps with the Curie transition of austenite. The martensitic transition appears to initially take place at the grain boundaries and then it extends to low temperature as the volume of the grains transforms to martensite.

In this work, results of structural studies, performed as a function of temperature (13–1073 K) of Na0.72CoO2 cathode material, are presented, together with microstructural measurements, including detailed transmission microscopy examination, as well as electrochemical studies, showing current rate-dependent charge/discharge characteristics and also voltammetry tests. It was found that thermal expansion of P2 type (P63/mmc) Na0.72CoO2 differs along a- and c-axes. Microstructural studies showed platelet-like grains of the synthesized sodium cobaltate, while detailed transmission microscopy measurements indicated coexistence of well-defined layered regions with regions having somewhat disturbed atomic arrangement. For higher current densities, characteristic plateaus observed on Na/Na+/NaxCoO2 charge/discharge curves diminish, and the voltage dependence on the sodium concentration is smoothed out. Results of the electrochemical tests, performed on cathodes without any carbon additives, indicated that in fact, such additives influence electrochemical behavior during first charge considerably. Additional voltammetry investigations confirmed presence of nine characteristic anodic and cathodic peaks, corresponding well with plateaus observed during charge/discharge of the cells.

Magnetic properties of a Ni50Mn35.5In14.5 Heusler ribbon were studied by ferromagnetic resonance (FMR) in the temperature range of 335–100 K. In the temperature region of 265–170 K, the FMR signal disappeared, in spite of the fact that this region comprised the main crystal transformation temperatures: Ms , Mf , As , Af . In the austenite crystal state, a weak antiferromagnetic interaction was observed, whereas ferromagnetism was detected in the low temperature martensitic state.

Copper matrix composites strengthened with graphene were prepared by vacuum uniaxial hot pressing of ball milled mixtures of powders. Two grades of graphene platelets were used; one with thickness of 10–20 nm and with lateral size of less than 14 μm and another with much lower thickness of platelets of 2–4 nm and in (002) plane crystallite size below 100 nm. Hot pressing in vacuum allowed obtaining composites containing 1 and 2 wt% of graphene. The addition of fine graphene led to about 50% higher hardness and about 30% lower electrical resistivity than composite with coarse graphene platelets. SEM studies of samples with fine graphene additions showed much more homogeneous microstructure than those containing coarse graphene. Based on TEM studies, copper particle size was estimated between 100 and 300 nm, and smaller in the areas of copper particle boundaries, where plastic deformation of copper particles brought about mixing nanocrystalline copper and graphene phases. Graphene conglomerates were identified using electron diffraction and often consisted of elongated platelets of thickness up to 20 nm in both graphene composites studied. Raman spectra confirmed nonhomogeneity of graphene in bulk composites and showed increase of defect density within graphene platelets, as was assessed from low intensity ratio I (2D)/ I (G), in places of high graphene concentration in both kinds of samples. The weak signal in more homogeneously distributed graphene in samples with fine graphene additions confirmed similar structural features, however the lateral size of finer graphene remain unchanged in composites, contrary to that with coarser graphene additions.

Two innovative systems based on feed-forward and recurrent neural network used for qualitative analysis has been applied to specimens of different fruit tea. Their performance was compared against the conventional methods of artificial intelligence. The proposed systems are a combination of data preprocessing methods, genetic algorithms and Levenberg–Marquardt (LM) algorithm used for learning feed forward and recurrent neural networks. The initial weights and biases of neural networks chosen by the use of genetic algorithms were then tuned with a LM algorithm. The evaluation was made on the basis of accuracy and complexity criteria. The main advantage of the proposed systems is the elimination of the random selection of the network weights and biases resulting in the increased efficiency of the systems.

An influence of the Cu doping on structural, magnetic and thermoelastic properties of the Heusler Ni44-xCuxCo6Mn39Sn11 (x = 1–4 at%) ribbons has been investigated. It is found that the addition of Cu stabilizes austenite phase. Martensite transformation (MT) temperatures generally decrease when Cu concentration increases, which is attributed to the atom size effect. The inverse magnetocaloric and elastocaloric effects in the vicinity of MT under moderate magnetic fields and stresses have been evaluated. Small Cu addition enhances both effects as compared to quaternary Ni–Co–Mn–Sn alloy. The magnetic entropy change under low magnetic field of 15 kOe increases from 2.9 J kg−1K−1 for Cu0 to 6.3 J kg−1K−1 for Cu2.

An electrospinning technology have been developed to obtain zinc oxide nanofibres doped with aluminum. Properties of the obtained nanostructures can be controlled by both the composition of a precursor and subsequent annealing treatment. The gas sensors manufactured with the use of ZnO:Al nanofibres exhibit good response to NO2 at relatively low operating temperatures. For some samples it was observed that interaction with ambient NO2 gas causes the change of conductivity from n-type to p-type at higher operating temperatures. This phenomenon was not observed for the samples annealed at higher temperature.

Presented work is focused on the use of correlation methods for numerical analysis of magnetic stray field over the surface of materials. Obtained results extend our previous findings about application of the autocorrelation function and the fractal analysis for characterization of magnetic surfaces. Several domain images are recorded at various tip-sample gaps (i.e. the lift heights), and then their average widths were extrapolated down to the zero distance in order to estimate the width seen right on the surface. Apart from that, fractal parameters were derived from autocorrelation function, which turned out to be sensitive to the lift height, and might constitute universal measure (the critical lift height), above which the MFM signal became dominated by thermal noises and non-magnetic residual interactions.

The influence of Al substitution for Sn on magnetocaloric properties and exchange bias behavior in Ni48Mn39.5Sn12.5−xAlx (x=0, 1, 2, 3) melt spun ribbons have been investigated. All the studied ribbons undergo a martensitic and reverse transformation. At low temperature martensite region, below 100 K, the alloys exhibit exchange bias effect, which appears to enhance with the increase of Al concentration. The loop shift difference (ΔHE) of up to 7960 A m−1 is recorded between the ribbon containing no Al and the ribbon with x=3. The presence of exchange bias behavior in these samples is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions. The magnetic entropy change and refrigerant capacity are evaluated for the ribbons studied around both the structural and magnetic transformations under the applied magnetic field induction of 2 T. The maximum entropy change around the magnetic transition and around the structural transition is reported for the Ni48Mn39.5Sn12.5 ribbon, and the entropy values amount to 1.8 and 7.8 J kg−1 K−1, respectively.

Four alloys with nominal compositions Ni46Mn41.5-xFexSn12.5 (x=0, 2, 4, 6 at.%) were cast in an induction vacuum furnace and homogenized. Then they were melted in quartz tubes and ejected onto a rotating copper wheel to produce ribbons. The X-Ray phase analyses of as melt spun ribbons have shown that in both, the ternary as well as in the quaternary alloys a single phase of the Heusler L21 type ordered structure was found. The characteristic temperatures of magnetic (TC) and martensitic (Ms) transformations were determined by a vibrating sample magnetometer (VSM). Both the Ms and TC increase with the increase of Fe content in all alloys, which is in accordance with the theory of valence electron concentration (e/a) influence on Ms. The phase structures, chemical compositions, grains sizes and type of microsegregation were characterized by transmission electron microscope (TEM). The equi-axed grains of size from 0.95 to 1.7 μm were observed in all ribbons. The grains posses the L21 structure at room temperature, however in the alloys with higher Fe content the different type of martensite was observed at the grain boundaries of L21 phase. Appearance of this martensite was explained in relation to microsegregation of particular elements during melt spinning process and simultaneous change in the e/a ratio.

Temperature dependence of twinning stress associated with type I twin boundaries in the Ni49.5Mn38.4Sn12.2 single crystal has been measured. At room temperature, the twinning stress amounts to 16.6 MPa, exceeding the typical values observed in the archetypical Ni-Mn-Ga alloys; nonetheless, it shows a remarkable sensitivity to temperature decreasing with a slope of 0.2498 MPa/K. This is a level of magnitude more than in Ni-Mn-Ga alloys. The remarkable sensitivity of twinning stress to temperature is primarily associated with the evolution of lattice parameters during heating. The type II twin boundaries in the same single crystal are activated at the twinning stress of 3.4 MPa, roughly one fifth of the twinning stress recorded for the type I twin boundaries. It is demonstrated that by careful compositional adjustments and thermomechanical training, it may be feasible to exercise magnetic field-induced strain due to twin variant rearrangement outside the Ni-Mn-Ga system.Temperature dependence of twinning stress associated with type I twin boundaries in the Ni49.5Mn38.4Sn12.2 single crystal has been measured. At room temperature, the twinning stress amounts to 16.6 MPa, exceeding the typical values observed in the archetypical Ni-Mn-Ga alloys; nonetheless, it shows a remarkable sensitivity to temperature decreasing with a slope of 0.2498 MPa/K. This is a level of magnitude more than in Ni-Mn-Ga alloys. The remarkable sensitivity of twinning stress to temperature is primarily associated with the evolution of lattice parameters during heating. The type II twin boundaries in the same single crystal are activated at the twinning stress of 3.4 MPa, roughly one fifth of the twinning stress recorded for the type I twin boundaries. It is demonstrated that by careful compositional adjustments and thermomechanical training, it may be feasible to exercise magnetic field-induced strain due to twin variant rearrangement outside the Ni-Mn-Ga system.

A prospective high temperature polycrystalline Ni50Mn44Sn6 Heusler shape memory alloy transforms at 637 K into 14 M and NM martensites with a14M = 6.278, b14M = 6.127, c14M = 5.654; and aNM = 5.449, cNM = 6.380 A lattice parameters, theoretically yielding 9.9% (14 M) and 14.6% (NM) mechanically induced strain due to detwinning of martensite in single crystal. The substitution of Ni for Co, Cu and Fe (5 at.%) brings the martensitic transformation to lower temperatures (ΔT = 129 K), whereas the martensite develops into NM (Co) and 6 M (Fe & Cu) structures offering up to 13.9% theoretical strain (Co; NM). The Ni45Fe5Mn44Sn6 alloy is singled out by non-uniform composition; i.e. the γ phase coexists with 6 M martensite, and a ferromagnetic order setting in below 301 K, whereas all other alloys are chemically homogenous and predominantly paramagnetic. The results qualify the studied alloys as interesting candidates for high temperature shape memory alloys applications.

Martensitic and magnetic transformations in Ni 48 Mn 39.5 Sn 12.5− x Al x ( x =0, 1, 2, 3) Heusler alloy ribbons were investigated. It is demonstrated that both magnetic and structural transformations occur in all of the studied samples. It is also shown that substitution of Sn with Al causes the martensitic transformation ( MT ) and the reverse martensitic transformation ( RMT ) temperatures to increase to room temperature (Δ T MT =49 K; Δ T RMT =43 K), whereas the Curie temperature of martensite T C M decreases (Δ T =36 K) and the Curie temperature of austenite T C A remains practically insensitive to Al introduction. This then allows to tune T C A and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L2 1 type structure has been identified to exist in all the samples regardless of composition. On the other hand the structure of martensite has been shown to be sensitive to composition. It has been determined as the 10 M martensite with ( 3 2 ¯ ) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity ( 3 1 ¯ ) in Al containing samples. In addition, the splitting of the field cooling ( FC ) and the field heating ( FH ) thermo-magnetic curves at low (50 Oe) magnetic field and below the T C M has been attributed to intermartensitic transition. The application of large magnetic field (50 kOe) has shown the existence of two distinct ferromagnetic states with a considerable hysteresis loop. The properties of these materials make them promising for magnetocaloric applications.

The magnesium alloy ZRE1 (2.7%Zn, 0.53%Zr, 3,14% rare earth elements) was applied as a matrix of composite reinforced with glassy carbon particles obtained by hot pressing of powder mixture. An influence of matrix chemical composition on interaction processes occurring at the interface was analyzed. The interface microstructure was characterized by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). It was revealed the continuous bonding between components and a presence of zone enriched with zirconium, rare earth elements and oxygen in comparison to the matrix composition.

The influence of Al substitution for Sn in Ni44Mn43.5AlxSn12.5-x(x= 0, 1, 2, 3) ferromagnetic shape memory alloy ribbons on phase transformation and microstructure evolution is outlined in this paper. Ribbons produced by melt spinning technique showed fully crystalline structure, however non uniform. Energy dispersive spectroscopy microanalysis (EDS) confirmed the average composition of ribbons in accord with the initial alloys. The higher symmetry parent phase was identified with the aid of X-ray diffraction (XRD) as bcc L21Heusler type structure. The unit cell parameters were determined applying the XRD profile fitting method. It was observed that with increase of Al content unit cell parameters and in turn unit cell volume decrease. This may be attributed to the fact that Al has a smaller radius compared to Sn, which it was substituted for. Differential scanning calorimetry (DSC) measurements did not allow to detect the martensitic transformation above -150°C.

Alloys with constant Ni/Mn ratio equal to 1.01 of nominal compositions Ni44Mn43.5Sn12.5-xAlx (x = 0, 1, 2 and 3) were induction cast, homogenized in vacuum for 6 hours at 1000ºC, annealed for 1 h at 900 and water quenched for solution treatment (ST). Differential scanning calorimetry (DSC) studies revealed that the quenched alloys undergo martensitic transformation with martensite start temperatures (Ms) ranging from - 140 up to - 80ºC. An increase of Ms temperature with increasing of the aluminum content as well as the linear relationship between Ms and the conductive electron concentration (e/a) was observed. DSC has been used also to estimate the associated entropy change from the transformation heat Q and peak position temperature Tp; corresponding to ΔS ≈ Q/Tp. X-Ray diffraction phase analyses performed at room temperature proved that in all ST alloys the L21 Heusler structure is present. However, a different degree of order of this phase was observed, what was manifested by a decrease of intensity of the 111 superlattice reflection of the L21 structure with an increase of Al content. The ordering behavior was also proven by the transmission electron microscopy (TEM) investigations, particularly electron diffraction patterns. The evolution of microstructure after different treatments was also illustrated by light microscopy observations.

The authors designed and manufactured the gas micropreconcentrator in micromachining technology. The structure is 1.68 mm thick and has lateral dimensions 2 cm by 2 cm. It contains the 12 cm long channel etched in Si wafer. The channel is covered from the upper side with a glass bonded anodically so as to permit for an easy inspection of the channel during the process of filling it with an adsorbent. At the bottom the Pt heater was deposited, necessary for heating the adsorbent to elevated temperatures during its activation and desorption processes. In the article the authors describe the micropreconcentrator simulations and technology processes together with thermal and preconcentration tests of manufactured structure. A few commercially available adsorbents from Sigma–Aldrich were selected and tested in order to concentrate low levels of acetone. The best concentration factor obtained was 830.

Commercial brass Ms36, 2mm thick was annealed and deformed in 6 passes in dual rolls equipment with attached equal channel equipment (DRECE). Then, material was deformed again using constrained groove pressing (CGP) by pressing of grooves 4.2 mm thick, and the groove angle of 45 deg. The experiment was performed 8 times (pressing out grooves and straightening at room temperature). Both methods allowed deformation without changing of the thickness of the sample, which was almost constant near 2 mm. The tensile experiment have shown the Yield Strength YS after 8x groove pressing of 210 MPa and Ultimate Tensile Strength UTS increased 27% up to 430 MPa. At the same time total elongation decreased from 34 to 15 %. The structure of the material after DRECE 6 passes was investigated using conventional TEM and have shown only rather uniform distribution of dislocations. After additional 8 groove pressing experiment, frequent, narrow deformation twins were observed accompanied by the formation of subgrains. Orientation imaging microscopy performed have shown average grain size after DRECE process near 5 μm, which decreased after 8 processes of groove pressing down to 2.9 μm. The fraction of low angle boundaries (below 5 deg) decreased after groove pressing down to 73% from 85% after DRECE process and annealing, while the fraction of high angle grain boundaries (>15 deg) increased after groove pressing up to 24% from 14%, however the total length of high angle boundaries increased more than 2 times since grain size decreased. The structure studies have shown rather mild effect on the grain refinement of both methods and they have to be modified to obtain material approaching nanosize range.

The alloys Al-12 wt % Zn-3 wt % Mg-1.5 wt % Cu with addition of Zr were melt spun and then hot pressed under 600 MPa pressure at 380 °C. Refinement of the microstructure and reduction of the volume fraction of the η (MgZn2) phase was observed in melt spun ribbon, as compared to the mould cast alloys. Good quality samples without pores and cracks obtained by hot pressing were composed of grains of size 0.2-0.5 µm. The particles of the η phase enriched in Zn, Mg and Cu were homogenously distributed in the matrix, while a few nanometres large precipitates of magnesium oxide were located at grain boundaries. Plate like precipitates of metastable h¢ phase appear after ageing at 120 °C and lead to microhardness increase up to about 195 HV as compared to 145 HV in pressed sample. Hot pressed ribbons showed compression strength of about 450 MPa which increased up to 630 MPa after ageing.

The concept to design a composite of the 7475 alloy strengthened with particles of an amorphous aluminum based alloy was studied in the present paper. Mechanical alloying (MA) process was applied to obtain amorphous structure of the powder of composition Al70Ni10Zr10Ti10 (in at%). Elemental powders of this composition were ball milled for 60 h in a planetary high energy mill using steel balls. The estimated mean size of powder particles below 10 μm was much smaller than that of the initial elemental powders. The mean value of the microhardness of the milled powder was 384 HV and was significantly higher than that of initial powders. The dominant presence of the amorphous structure was confirmed using DSC studies, in which crystallization peaks were observed above 400°C. X-ray diffraction (XRD) patterns after various milling times confirmed a partial amorphization of the material. Additionally, weak maxima of Al3Zr4 phase were identified. TEM studies of powders confirmed the formation of predominantly amorphous structure with some nanocrystalline inclusions of intermetallic phases identified as Al3Zr4, AlZr3, Al3Ni and Al3Ti. The amorphous powder was mixed (for a short time) with prealloyed 7475 alloy powder 40 h ball milled to obtain nanocrystalline grain size of powder’s particles. Powders were hot pressed in vacuum, below the crystallization temperature at 380°C and pressure of 600 MPa in order to preserve amorphous and nanocrystalline grain structure. SEM studies of the composite containing 1/3 ball milled 7475 alloy and 2/3 of the amorphous powder allowed identifying low porosity and clean interface within the composite. The samples showed compression strength near 500 MPa and a few percent ductility. The cracks nucleated within the amorphous particles as resulted from SEM studies of the compressed samples.

The rapid solidification of Al-12 Zn-3 Mg-1.5 Cu (in mass%) alloy was investigated in order to determine structure changes and the effect of Zr or Sc+Zr additions. Rapidly solidified ribbons with the thickness of 30–50 mm were obtained by a melt spinning technique. The alloys cast into a copper mould were used as a reference material. The mould cast alloys as well as the melt spun ribbons revealed the dendritic microstructure of(Al) solid solution and (MgZn2) phase in the interdendritic areas. Additionally the T-Mg32(Zn, Al)49 phase with icosahedral quasicrystalline symmetry was found in the form of small particles located mainly at the wheel side in the Zr or Zr+Sc containing ribbons. The refinement of the microstructure and the reduction of volume fraction of the phase was observed in the ribbons. Large Al3Zr primary precipitates were observed in the mould cast alloy containing zirconium, while almost whole Zr in the ribbons dissolved in the aluminium solid solution. Annealing of ribbons at 400 � C led to the precipitation of spherical L12-Al3Zr or Al3(Sc, Zr) particles, coherent with the matrix. They could be responsible for the improvement of properties of the aluminium alloys by the retardation of recrystallization and grain growth. Plate like precipitates of metastable 0 phase appeared after ageing at 120 � C and led to the increase of microhardness up to about 230 HV. [doi:10.2320/matertrans.MB201009]