Growth of large single-grain decagonal quasicrystal by directional solidification of undercooled Al<Subscript>72</Subscript>Ni<Subscript>12</Subscript>Co<Subscript>16</Subscript> alloy melt

The growth of decagonal quasicrystals was investigated by the directional solidification of highly undercooled Al₇₂Ni₁₂Co₁₆ melts. The maximum single-grain decagonal quasicrystal contained in the grown crystals was about 0.5 mm in diameter and 6 mm in length. The quality of the grown crystals was examined by the X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM).     

High-temperature superelasticity during B2-L1<Subscript>0</Subscript> martensite transformations in Co<Subscript>40</Subscript>Ni<Subscript>33</Subscript>Al<Subscript>27</Subscript> crystals

The temperature interval ΔT _SE of superelasticity in [001]-oriented Co₄₀Ni₃₃Al₂₇ (at. %) single crystals strained by tension and compression has been studied. It is established that ΔT _SE in tension amounts to 220 K, and the reversible B2-L1₀ martensite transformations in loaded samples take place at 590 K. In the samples strained by compression, ΔT _SE decreases to 105 K, and the superelasticity is observed up to 420 K.     

Phase quantification of impulse atomized Al<Subscript>68.5</Subscript>Ni<Subscript>31.5</Subscript> alloy

Powders of Al_68.5Ni_31.5 were produced using the impulse atomization technique. The molten droplets were cooled in-flight by the stagnant helium or nitrogen in the atomizing chamber, and the resulting powders were sieved into different size ranges. Scanning electron microscopy, X-ray diffraction, and neutron diffraction were used in order to study the microstructure and to quantify the phase fractions in the samples. The computer software GSAS was used to calculate the weight fraction of the existing phases, namely Al₃Ni₂, Al₃Ni, and Al, by the profile refinement method. X-ray micro-tomography and optical microscopy were used to study the porosity formation inside the particles. It was found that for particles having sizes decreasing from 925 to 256 μm (increasing cooling rate), the weight fraction of Al₃Ni and eutectic Al decreases while that of Al₃Ni₂ increases. Furthermore, the droplets formed at higher cooling rates yielded a lower volume fraction of porosity.     

Martensitic phase transformation in single crystal Co<Subscript>5</Subscript>Ni<Subscript>2</Subscript>Ga<Subscript>3</Subscript>

The magnetic, thermal, and transport properties of martensitic phase transformation in single crystal Co₅Ni₂Ga₃ have been investigated. The single crystal Co₅Ni₂Ga₃ shows martensitic transformation at 251 K on cooling and 254 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve, and temperature-dependent thermal conductivity curve are observed at martensitic transformation temperature (T _M). Negative magnetoresistance due to spin disorder scattering was observed in Co₅Ni₂Ga₃ single crystal at all temperature range. The temperature-dependent negative magnetoresistance shows a peak at T _M, which indicates that the spin disorder increases in the process of phase transition. Co₅Ni₂Ga₃ sample exhibits a temperature dependence of thermal conductivity κ(T) (dκ/dT > 0) due to electrons being above temperature 100 K.     

Effects of metal oxides addition on the electrochemical performance of M1Ni<Subscript>3.5</Subscript>Co<Subscript>0.6</Subscript>Mn<Subscript>0.4</Subscript>Al<Subscript>0.5</Subscript> hydrogen storage alloy

The AB₅-type M1Ni_3.5Co_0.6Mn_0.4Al_0.5 alloy (where M1 denotes mixed lanthanide) was modified with different additives (ZnO and MnO₂), and the effects of metal oxides on the electrochemical properties of the M1Ni_3.5Co_0.6Mn_0.4Al_0.5 − x% M (x = 5, 10; M = ZnO, MnO₂) alloy were studied. The results showed that the addition of metal oxides had a positive effect on the activation property of the alloy electrode. With the addition of ZnO, the maximum discharge capacity of the alloy increased from 315 to 334 mAh/g (x = 5) and 341 mAh/g (x = 10) with good cycle capability (C ₃₀/C _max) (87% for x = 5 and 85% for x = 10), while the maximum discharge capacity remained invariable and the cyclic stability was deteriorated by the addition of MnO₂. Linear polarization (LP), cycle voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements were also performed to investigate the electrochemical kinetics of alloy electrodes.     

Reactive Stresses in Ni<Subscript>49</Subscript>Fe<Subscript>18</Subscript>Ga<Subscript>27</Subscript>Co<Subscript>6</Subscript> Shape-Memory-Alloy Single Crystals

The reactive stresses induced in Ni₄₉Fe₁₈Ga₂₇Co₆-alloy single crystals during martensitic transformations with a limited possibility of shape-memory-strain recovery have been experimentally studied. The data on these crystals are compared with the results obtained previously for Cu–Al–Ni, Ni–Ti, and Ni?Fe–Ga crystals. The potential of application of the Ni₄₉Fe₁₈Ga₂₇Co₆ single crystals in designing drives and power motors is demonstrated.     

Microstructure and high-temperature strength of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary melt growth composite

A new Al₂O₃/Er₃Al₅O₁₂(EAG)/ZrO₂ ternary MGC (Melt Growth Composite) with a novel microstructure has been fabricated by unidirectional solidification. This ternary MGC has a microstructure consisting of continuous networks of single-crystal Al₂O₃, single-crystal EAG and fine cubic-ZrO₂ phases without grain boundaries. The ternary MGC has also characteristic dimensions of the microstructure of around 2–4 m for EAG phases, around 2–4 m for Al₂O₃ phases reinforced with around 0.4–0.8 m cubic-ZrO₂ phases. No amorphous phases are formed at interfaces between phases in the ternary MGC. The ternary MGCs flexural strength at 1873 K is approximately 700 MPa, more than twice the 330 MPa of the Al₂O₃/EAG binary MGC. The fracture manner of the Al₂O₃/EAG/ZrO₂ ternary MGC at 1873 K shows the same intergranular fracture as the Al₂O₃/EAG binary MGC, but is significantly different from the transgranular fracture of the sintered ceramic.     

Crystallization kinetics of an amorphous Al<Subscript>75</Subscript>Ni<Subscript>10</Subscript>Ti<Subscript>10</Subscript>Zr<Subscript>5</Subscript> alloy

The formation and crystallization behaviors of a mechanically alloyed Al₇₅Ni₁₀Ti₁₀Zr₅ amorphous alloy were studied by X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry in the present study. The effective activation energy of the crystallization was determined by the Kissinger and Ozawa equations, respectively. The two equations yield close results and the average activation energy is 252 ± 13 kJ/mol. The resultant crystalline products were Al and Al₃Ni, and the crystallization mechanism is two- or three-dimensional nucleation and growth controlled by the diffusion of atoms. The thermal stability of the alloy was evaluated by a continuous transformation diagram obtained by the extended Kissinger equation.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Evolution of the microstructure and mechanical properties of eutectic Fe<Subscript>30</Subscript>Ni<Subscript>20</Subscript>Mn<Subscript>35</Subscript>Al<Subscript>15</Subscript>

The microstructure of the eutectic alloy Fe₃₀Ni₂₀Mn₃₅Al₁₅ (in at.%) was modified by cooling at different rates from 1623 K, i.e., above the eutectic temperature. The lamellar spacing decreased with increasing cooling rate, and in water-quenched specimens lamellae widths of ~100 nm were obtained. The orientation relationship between the fcc and B2 lamellae was found to be sensitive to the cooling rate. In a drop-cast alloy the Kurdjumov–Sachs orientation relationship dominated, whereas the orientation relationship in an arc-melted alloy with a faster cooling rate was \textfcc( [`1]12 )//\textB2( 0 1 1 );  \textfcc[ 1[`1]1 ]//\textB2 [ 1[`1]1 ]  \textand \textfcc( 0[`1]1 )//\textB2( 00 1 );\text fcc[ 0 1 1 ]//\textB2[ [`1][`1]0 ] {\text{fcc}}\left( {\bar{1}12} \right)//{\text{B2}}\left( {0 1 1} \right);\;{\text{fcc}}\left[ {1\bar{1}1} \right]//{\text{B2 }}\left[ {1\bar{1}1} \right] \,{\text{and}}\,{\text{fcc}}\left( {0\bar{1}1} \right)//{\text{B2}}\left( {00 1} \right);{\text{ fcc}}\left[ {0 1 1} \right]//{\text{B2}}\left[ {\bar{1}\bar{1}0} \right] . The hardness increased with microstructural refinement, obeying a Hall–Petch-type relationship. The strength of the alloy decreased significantly above 600 K due to softening of the B2 phase.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Laser multi-layer cladding of Zr<Subscript>65</Subscript>Al<Subscript>7.5</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>17.5</Subscript> amorphous alloy on magnesium substrates

A coating about 3-mm thick of the amorphous alloy, Zr₆₅Al_7.5Ni₁₀Cu_17.5 was fabricated on magnesium substrates using the technique of laser multi-layer cladding protected under an atmosphere of argon gas. The coating exhibited a graded microstructure, which could be generally categorized into three classes: an amorphous phase, an amorphous–nanocrystalline composite, and one which is predominantly crystalline. Formation of the latter two was due to the reheating effect of the laser cladding process. With regard to properties, the microhardness and the wear resistance of the composite material were both higher than that of the monolithic amorphous material; both materials showed excellent corrosion resistance in a 3.5% NaCl solution.     

Au/Ni<Subscript>12</Subscript>P<Subscript>5</Subscript> core/shell single-crystal nanoparticles as oxygen evolution reaction catalyst

We have demonstrated the improved performance of oxygen evolution reactions (OER) using Au/nickel phosphide (Ni₁₂P₅) core/shell nanoparticles (NPs) under basic conditions. NPs with a Ni₁₂P₅ shell and a Au core, both of which have well-defined crystal structures, have been prepared using solution-based synthetic routes. Compared with pure Ni₁₂P₅ NPs and Au-Ni₁₂P₅ oligomer-like NPs, the core/shell crystalline structure with Au shows an improved OER activity. It affords a current density of 10 mA/cm² at a small overpotential of 0.34 V, in 1 M KOH aqueous solution at room temperature. This enhanced OER activity may relate to the strong structural and effective electronic coupling between the single-crystal core and the shell.

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Microstructure and H<Subscript>2</Subscript>S gas sensing properties of nanocrystalline perovskite-type La<Subscript>0.6</Subscript>Co<Subscript>0.4</Subscript>Mn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Nanocrystalline La_1−x Co _x Mn_1−y Ni _y O₃ (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H₂S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H₂S gas response of pure LaMnO₃ was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and B-site, respectively. The La_0.6Co_0.4Mn_0.5Ni_0.5O₃ shows high response towards H₂S gas at an operating temperature 250 °C. The Pd-doped La_0.6Co_0.4Mn_0.5Ni_0.5O₃ sensor was found to be highly sensitive to H₂S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed.     

Crystallization behaviour and mechanical properties of rapidly solidified Al<Subscript>87.5</Subscript>Ni<Subscript>7</Subscript>Mm<Subscript>5</Subscript>Fe<Subscript>0.5</Subscript> amorphous alloy

The crystallization behaviour and the mechanical properties of rapidly solidified Al_87.5Ni₇Mm₅Fe_0.5 alloy ribbons have been examined in both as-melt-spun and heat-treated condition using differential scanning calorimetry, X-ray diffractometry (XRD), transmission electron microscopy (TEM), tensile testing and Vicker’s microhardness machine. XRD and TEM studies revealed that the as-melt-spun ribbons are fully amorphous. The amorphous ribbon undergoes three-stage crystallization process upon heating. Primary crystallization resulted in the formation of fine nanocrystalline fcc-Al particles embedded in the amorphous matrix. The second and third crystallization stages correspond to the precipitation of Al₁₁(La,Ce)₃ and Al₃Ni phases, respectively. Microhardness and tensile strength of the ribbons were examined with the variation of temperature and subsequently correlated with the evolved structure. Initially, the microhardness of the ribbon increases with temperature followed by a sharp drop in hardness owing to the decomposition of amorphous matrix that leads to formation of intermetallic compounds     

Structural,Thermal and Magnetic Properties of Nanocrystalline Co<Subscript>80</Subscript>Ni<Subscript>20</Subscript> Alloy Prepared by Mechanical Alloying

Co₈₀Ni₂₀ powder mixture was mechanically alloyed by high-energy planetary ball milling, starting from elemental Co and Ni metal powders. The morphological, microstructural, thermal and magnetic properties of the milled powders were characterised respectively by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and vibratory sample magnetometry. In addition to a highly disordered phase, two face-centred cubic (FCC) and hexagonal close-packed (HCP), solid solutions, FCC Co(Ni), FCC Ni(Co) and HCP Co(Ni), are observed after 3 h of milling. Their grain sizes decrease with increase in milling time attaining, at 48 h of milling, 12 nm, 25 nm and 10 nm, respectively. Beyond a certain milling time, no further refinement of the microstructure occurs and the morphological equilibrium is usually given by a bimodal particle size distribution. Magnetic measurements of the milled Co₈₀Ni₂₀ alloy powder exhibit a soft ferromagnetic character where the magnetic parameters are sensitive to the milling time mainly due to the particle size refinement as well as the formation of Co(Ni) and Ni(Co) solid solutions. Both the saturation magnetisation ( M _s) and coercivity ( H _c) were found to decrease with milling time, attaining the values of M _s = 126 emu/g and H _c = 60 Oe after 48 h of milling.     

Li-ion storage performance and electrochemically induced phase evolution of layer-structured Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode material

Li-rich Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ (LMNC) powders were synthesized by a gel-combustion method. The related microstructure, electrochemical performance and electrochemically induced phase evolution were characterized. The 900°C calcined powders have a hexagonal layered structure with high ordered degree and low cationic mixing level. The calcined materials as cathode electrode for Li-ion battery deliver the high electrochemical properties with an initial discharge capacity of 243.5 mA?h?g^–1 at 25 mA?g^–1 and 249.2 mA?h?g^–1 even after 50 cycles. The electrochemically induced phase evolution investigated by a transmission electron microscopy indicates that Li⁺ ions deintercalated first from the LiMO₂ (M = Mn, Co, Ni) component and then from Li₂MnO₃ component in the LMNC during the charge process, while Li⁺ ions intercalated into Li_1–xMO₂ component followed by into MnO₂ component during the discharge process.     

Directional solidification and growth characteristics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary eutectic ceramic by laser floating zone melting

Directionally solidified Al₂O₃/Er₃Al₅O₁₂/ZrO₂ ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V ^?1/2. The temperature gradient has been measured to be about 5.3 × 10³ K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.     

Influence of iron additives on the corrosion resistance of Al<Subscript>87</Subscript>Gd<Subscript>5</Subscript>Ni<Subscript>8</Subscript> amorphous metal alloy

Based on the results of voltammetric investigations, we have shown that the partial replacement of nickel by 4 at. % Fe in Al₈₇Gd₅Ni₈ amorphous alloy leads to a decrease in the corrosion currents and an increase in the polarization resistance, which demonstrates the higher corrosion resistance of Al₈₇Gd₅Ni₄Fe₄ alloy. Using the method of electrochemical impedance spectroscopy, we have studied the durability and protective capacity of passivation oxide layers at electrodes made of this alloy in 0.1 M NaCl aqueous solution. We have also selected an impedance model of the formation of interfaces oxide–0.1 M NaCl and amorphous metal alloy–0.1 M NaCl. We have established that active diffusion redox reactions, described by the Warburg element, take place at the interface oxide film–0.1 M NaCl. The diffusivities of anions from the solution into the surface oxide layer have been calculated. Finally, we show that, with increase in the time of electrochemical reaction in 0.1 M NaCl aqueous solution, diffusion decreases due to the compaction of the surface oxygen-containing layers.