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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).

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.

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.

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&ndash, 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&ndash, B. Rutile nanopowder spread over the ethanol/chloroform/water formed a suspension, which was used as a source in L&ndash, 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 &deg, 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 &deg, C to 12 (19) s at 385 &deg, 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 &deg, C and systematically decreased upon increase in the operating temperature up to 400 &deg, C.

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.

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.

Ribbons of a Ni55Fe19Ga26 Heusler alloy were prepared by melt spinning technique. The effect of pressure on magnetostructural transitions was studied comparing as-spun ribbons to ribbons previously submitted to an axial pressure and to powder obtained from manually grinded as-spun ribbons. The martensitic transformation present in the as-spun ribbon almost vanishes after pulverization. The structural change driven by mechanical treatment is a stress-induced intermartensitic transformation from a 14 M modulated to a non-modulated tetragonal (NM) structure. There is a progressive change from the structure of as-spun samples to that of the pulverized one in samples submitted to axial pressures as it increases.

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.

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.

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.

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.

The paper describes the process of TiO2-SnO2 nanocompositesmanufacturing utilizing two-step sol-gel method combined with calcination (in the case of titanium hydroxide gel) or hydrothermal treatment (in the case of tin hydroxide). Phase composition of the obtained nanopowders and average crystallite sizes were determined using XRD analysis. Measurements of the specific surface area were performed using sorption method based on determination of physical adsorption isotherm (BET). Morphology of the nanopowders was observed using transmission electron microscope. The presented synthesis method enables to obtain composites nanopowders from TiO2-SnO2 system with known and controlled chemical and phase compositions, and distinctly diversified TiO2 and SnO2 particle sizes.

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.

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.

2D TiO2 thin films and 3D flower-like TiO2-based nanostructures, also decorated with SnO2, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO2-based sensing materials were investigated. 2D TiO2 thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO2 showed the best performance for H2 detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH3)2 after sensitization by SnO2 nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO2-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor.

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.

In this paper we describe structural, optical and electrical properties of nanocrystalline TiO 2 , SnO 2 and their composites obtained by the sol–gel method. The materials were characterized by X-ray diffraction (XRD), surface area estimated from the N 2 physisorption isotherm (BET), high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). Moreover, the paper examines optical and electrical properties of nanocomposites. In fact attention is particularly focused on the properties of the composites with various chemical compositions. An abrupt change in the optical and electrical properties has been observed, passing from the sample with the maximum amount of TiO 2 to a maximum amount of SnO 2 . The sensor made of composite containing 58.5% of SnO 2 exhibited the best NH 3 sensing features.

Electrode materials in which tin nanograins are encapsulated in carbon matrix obtained from different origin (starch or modified polymer) were examined. Morphology of the C/Sn composites was observed using transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) analysis in different states of charge (SOC) at initial cycle together with a long term galvanostatic charge-discharge cycling tests allowed determining the influence of carbon coating origin on the electrochemical behaviour of C/Sn nanocomposites. X-ray photoelectron spectroscopy (XPS) measurements of C/Sn materials before cycling and after first cycle were performed to observe changes in surface composition of the material which occur during electrochemical reaction. The results of surface characterization as well as electrochemical studies of C/Sn nanocomposites indicated that the origin of carbon precursor has a major impact on the composites’ morphology and electrochemical behaviour. Long term galvanostatic charge-discharge cycling tests proved that the carbon obtained from MPNVF precursor allows better encapsulation of tin nanograins in the buffer matrix. Furthermore, according to the XPS studies carbon coating based on MPNVF is more chemically stable versus electrolyte, which contributes directly to the improved protection of active material against physical damage. The charge capacity of MPNVF-based composite was 589 mAh g−1 after 70 cycles, which constitutes 59% of theoretical metallic tin capacity.

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.

This paper presents the acetone sensing characteristics of Si-doped (1 at.%) tungsten oxide thin films prepared by glancing angle dc magnetron sputtering. The performance of Si-doped WO3 sensors in the concentration range of 0.04–3.8 ppm at operating temperatures of 150 °C–425 °C has been investigated. Doping of the tungsten oxide film with Si significantly decreases the limit of detection of acetone compared with the pure WO3 sensors reported in the literature. The gas sensor’s response ( $S$ ) to acetone was defined as the resistance ratio $S = R_{\mathrm{ air}}/R_{\mathrm{ gas}}$ , where $R_{\mathrm{ air}}$ and $R_{\mathrm{ gas}}$ are the electrical resistances for the sensor in air and in gas, respectively. The maximum response measured in this experiment was $S=40.5$ . Such response was measured in the presence of 3.8 ppm of acetone at an operating temperature of 425 °C using a Si-doped (1 at.%) WO3 thin film deposited at 300 °C and annealed at 300 °C for 4 h in air. The films phase composition, microstructure, and surface topography have been assessed by X-ray diffraction, scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectroscopy methods.

In this paper, the investigation results on preconcentration of acetone at various initial concentrations are presented. The structures were made of conventional materials, such as stainless steel, quartz tube as well as fabricated in MEMS technology - micropreconcentrators. All structures have the same ‘active’ area to obtain more suitable comparison. The adsorbent materials were selected from commercial available Sigma-Aldrich Carbon Adsorbent Sampler Kit, consisting of 8 various adsorbents. The highest concentration factors were obtained by utilization of micropreconcentrator filled with Carboxen-1018, which is recommended for adsorption of C2-C3 compounds. The preconcentrators were placed into microsystem, and semiconductor gas sensor array was used as a detector unit. The microsystem was previously tested and designed for exhaled breath acetone analysis. The obtained results show that micropreconcentrator can be a useful tool for an increasing sensor sensitivity.

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.

Molds made of tool steels used in aluminum high-pressure die casting should routinely withstand tens of thousands of injection cycles, but repeated loading and temperature spikes result in their frequent premature wear. Extending their lifetime could be sought by nitriding or application of coatings of even higher hardness or both. Therefore, in the present experiment the arc-deposited Cr/(CrN)/nx(CrN/CrAlN)/mx(CrAlN/VN) or Cr/(CrN)/nx(CrN/TiAlN)/mx(TiAlN/VN) nano-multilayer stacks were deposited on glow discharge nitrided X40CrMoV5.1 steel. The scanning and transmission electron microscopy backed by Energy Dispersive X-ray Spectroscopy measurements of local chemical composition helped to confirm that the coatings are built of nanolayers of respective nitrides of period less than 10 nm. They also showed that droplets being characteristic for arc deposition method were enriched either in chromium, aluminum or vanadium but not in titanium. Both coatings presented comparable hardness of ~25 GPa, but the one covered with TiAlN/VN was roughly twice as wear resistant as the CrAlN/VN. Simultaneously, they were ~200 and ~100 more wear resistant than X40CrMoV5.1reference steel.

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.

In present work we were analysing thin layers of Ni-Co-Mn-In alloys, grown by pulsed laser deposition method (PLD) on Si, NaCl and glass substrates. For target ablation the second harmonics of YAG:Nd 3+ laser was used. The target had the composition Ni 45 Co 5 Mn 34.5 In 14.5 . The morphology of the layers and composition were studied by electron microscopy TESCAN Vega3 equipped with microanalyzer EDS – Easy EdX system working with Esprit Bruker software. The X-ray diffraction measurements (XRD), performed on spectrometer Bruker XRD D8 Advance system, reveals Ni 2 -Mn-In cubic phase having lattice constant a = 6.02A.

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.

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.

Vanadium pentoxide thin films were deposited onto insulating support by means of rf reactive sputtering from a metallic vanadium target. Argon-oxygen gas mixtures of different compositions controlled by the flow rates were used for sputtering. X-ray diffraction at glancing incidence (GIXD) and Scanning Electronic Microscopy (SEM) were used for structural and phase characterization. Thickness of the films was determined by the profilometry. It has been confirmed by GIXD that the deposited films are composed of V2O5 phase. The gas sensing properties of V2O5 thin films were investigated at temperatures from range 410&ndash, 617 K upon NO2 gas of 4&ndash, 20 ppm. The investigated material exhibited good response and reversibility towards nitrogen dioxide. The effect of metal-insulator transition (MIT) on sensor performance has been observed and discussed for the first time. It was found that a considerable increase of the sensor sensitivity occured above 545 K, which is related to postulated metal-insulator transition.

Ni49.4Mn38.5Sn12.1 near single crystal was obtained by the Bridgman method. At room temperature, it consisted of a mixture of the parent austenite phase with the cubic L21 Heusler structure (ac = 5.984 A) and modulated, tetragonal martensite phase 4M (at = 4.337 A, ct = 5.655 A). Under the application of a magnetic field, the specimen undergoes field induced reverse martensitic transformation, which combined with the Curie transition in austenite leads to the coexistence of direct and inverse magnetocaloric effects. The maximum entropy change at 280 K and under 5 T amounts to 3.4 J·kg−1·K−1 for the structural transition and at 316 K reaches −2.7 J·kg−1·K−1 for the magnetic transformation. The magnetic entropy change occurs over a wide temperature span leading to improved refrigerant capacity of 101 J·kg−1 (5 T). Hysteretic losses are considerably reduced, which is promising with respect to improved cyclic stability of such a material.