Melt-extraction Technique Research Articles

Giant magnetocaloric effect and hysteresis loss in MnxFe2-xP0.5Si0.5 (0.7 ≤ x ≤ 1.2) microwires at ambient temperatures

Magnetocaloric microwires are very promising for energy-efficient magnetic refrigeration in micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS). Creating microwires that exhibit large magnetocaloric effects around room temperature represents an important but challenging task. Here, we report a tunable giant magnetocaloric effect around room temperature in MnxFe2-xP0.5Si0.5 (0.7≤x ≤ 1.2) microwires by utilizing a melt-extraction technique paired with thermal treatment and chemical engineering. The isothermal magnetic entropy change (ΔSiso) and Curie temperature (TC) can be tuned by adjusting the Mn/Fe ratio. The TC varies from 351 to 190 K as x increases from 0.8 to 1.2. Among the compositions investigated, the x = 0.9 sample shows the largest value of ΔSiso = 18.3 J kg−1 K−1 for a field change of 5 T around 300 K. After subtracting magnetic hysteresis loss, a large refrigerant capacity of ∼284.6 J kg−1 is achieved. Our study paves a new pathway for the design of novel magnetocaloric microwires for active magnetic refrigeration at ambient temperatures.

Thermochemical Analysis of Hydrogenation of Pd-Containing Composite Based on TiZrVNbTa High-Entropy Alloy

The microcalorimetric hydrogen titration technique combined with conventional volumetric measurements has been used to reveal peculiarities of the hydrogenation of the single-phase TiZrVNbTa equiatomic high-entropy alloy. The alloy has been produced in the form of microfibers by the pendent drop melt extraction technique. Palladium coating of the fibers has been applied to enable first hydrogenation at room temperature without additional activation. An analysis of the obtained data allows us to evaluate the dependence of hydrogenation enthalpy on the hydrogen concentration in the alloy. Three concentration ranges, presumably related to the formation of the hydrogen solid solution, monohydride and dihydride phases, have been identified, and the corresponding ΔH values of about −100, −80 and −60 kJ/mol H2, respectively, have been determined.

Measurements and predictions of diffusible hydrogen escape and absorption in catholically charged 316LN austenitic stainless steel

Hydrogen can have an impact on the service life of safety critical components, such as coolant pipes in nuclear reactors, where it may interact with other factors including irradiation. Hence, it is important to characterise such behaviour which in turn requires the capability to charge representative material specimens with hydrogen and to quantity the levels of hydrogen present. Hydrogen concentrations resulting from cathodic charging of 316LN stainless steel over short time periods (< 2 h) were estimated from hydrogen release rates obtained from potentiostatic discharge measurements and used to calibrate simulations based on Fick’s second law of diffusion in order to predict the hydrogen concentration after 24 h of charging. Leave-one-out cross-validation was used to establish confidence in results which were also validated using measurements from the melt extraction technique. The success of Fick’s second law for estimating escape rates showed that a majority of the absorbed hydrogen was diffusible rather than trapped. These results confirmed that the potentiostatic discharge technique can be used on materials with low diffusivity, and provide a new method through which hydrogen concentrations within a sample can be estimated after cathodic charging non-destructively without the need to remove samples from solution.

Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane

Abstract. Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH4) to short-lived trace gases like ethane (C2H6) and propane (C3H8). Recently, the comparison of CH4 records obtained using different extraction methods revealed disagreements in the CH4 concentration for the last glacial in Greenland ice. Elevated methane levels were detected in dust-rich ice core sections measured discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH4 excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14:2:1, indicating a shared origin. The measured carbon isotopic signature of excess methane is (-47.0±2.9) ‰ and its deuterium isotopic signature is (-326±57) ‰. With the co-production ratios of excess alkanes and the isotopic composition of excess methane we established a fingerprint that allows us to constrain potential formation processes. This fingerprint is not in line with a microbial origin. Moreover, an adsorption–desorption process of thermogenic gas on dust particles transported to Greenland does not appear very likely. Instead, the alkane pattern appears to be indicative of abiotic decomposition of organic matter as found in soils and plant leaves.

Using Melt Extraction Technique to Produce Polypropylene/TiO2-Coated Stainless Steel Wrapped Yarns and Functional Fabrics: Evaluations of UV Resistances and Electromagnetic Shielding

Using Melt Extraction Technique to Produce Polypropylene/TiO2-Coated Stainless Steel Wrapped Yarns and Functional Fabrics: Evaluations of UV Resistances and Electromagnetic Shielding

Design of Fe-containing GdTbCoAl high-entropy-metallic-glass composite microwires with tunable Curie temperatures and enhanced cooling efficiency

Through designing the composition and processing approach, the non-equiatomic (Gd36Tb20Co20Al24)100-xFex (x = 0, 1, 2 and 3 at.%) high-entropy-metallic-glass (HE-MG) alloy microwires were successfully fabricated by melt-extraction technique. The microstructure and magnetocaloric properties of the microwires were systematically investigated. The microwires possess tunable Curie temperatures, i.e. 81–108 K, above the typical rare-earth (RE) containing HE-MG reports. The high Curie temperatures are attributed to the designed composition. Magnetocaloric response peak values of Fe-containing GdTbCoAl alloy microwires range 7.6–8.9 J kg−1 K−1 (5 T), which are comparable to those of many outstanding RE-containing magnetocaloric HE-MGs. The characteristics of the melt-extraction method, combining with compositional effects, favor the formation of amorphous and nanocrystalline phases. The increase in the cooling efficiency for microwires with higher Fe content can be attributed to the broadening of the Curie temperature distribution induced by the composition difference between nanocrystalline phase and amorphous matrix. The designed composition and the melt-extraction processing approach for Fe-containing GdTbCoAl alloys can tune their Curie temperatures towards a temperature range of natural gas liquefaction and improve their magnetocaloric properties. This demonstrates that Fe-containing GdTbCoAl HE-MG composite microwires have great potential as high-performance magnetic refrigerants.

Exchange bias and spin-reorientation transition in α-Fe/PrDyCoFeB core/shell microwires

Magnetic anisotropy and interface exchange interaction were analyzed in α-Fe core microwire covered with PrDyCoFeB amorphous shell. The α-Fe/PrDyCoFeB core/shell microwires were grown by pendant drop melt extraction technique providing separation of the α-Fe and PrDyCoFeB phases during the ultrafast cooling. Low saturation field of the core ~100 Oe and high saturation field of amorphous shell ~10 kOe with zero coercivity were distinguished from angular dependences of the magnetic moment, recorded in low and high magnetic fields. Sharp decrease of the longitudinal magnetization, effective anisotropy field and magnetic susceptibility have been observed below the critical temperature, Tcrit = 240 K, in zero field. The Almeida-Thouless transition from ferrimagnetic state to Ising spin glass state has been revealed in PrDyCoFeB amorphous shell. Such spin reorientation transition is very attractive for magnetocaloric applications. We found exchange bias effect controlled by exchange coupling between ferromagnetic core and ferrimagnetic shell. The significance of the obtained data lies in possible applications of the core/shell microwires for tweezers with magnetic moment, stepwise changing in external field. Exchange bias in core-shell interface provides determined initial state of the microwire used as working media of field sensor. The sharp decrease of the magnetization associating with spin-reorientation transition looks very promising for magnetocaloric applications close to room temperature.

Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires**Project supported by the National Natural Science Foundation of China (Grant Nos. 51701099, 51801044, and 51671071), the Natural Science Foundation of Heilongjiang Province of China (Grant No. LH2019E091), and Fundamental Research Funds in Heilongjiang Provincial Universities, China (Grant No. 135409320). Thanks to the help of Technology Innovation

Ni50Mn25Ga20Fe5 ferromagnetic shape memory alloy microwires with diameters of ∼ 30–50 μm and grain sizes of ∼ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni50Mn25Ga20Fe5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (> 96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.

Magnetocaloric effect in Ni–Fe–Mn–Sn microwires with nano-sized γ precipitates

Ni45.6Fe3.6Mn38.4Sn12.4 microwires, with nanoscale γ-phase precipitates that enhance the magnetocaloric effects (MCEs) and mechanical properties, were prepared by a melt-extraction technique and subsequent high temperature annealing. The atomic ordering degree significantly increased after annealing, leading to a considerable increment in the structural entropy change (ΔStr) from 4.5 J/kg·K in the as-extracted microwire to 26.6 J/kg·K in the annealed one, and the magnetization difference (ΔM) from 35 A·m2/kg to 51 A·m2/kg under a magnetic field of 5.0 T. Consequently, a positive magnetic entropy change (ΔSM) peak of 15.2 J/kg·K with working temperature span (ΔTFWHM) of 12 K for the first-order martensite transformation followed by a negative ΔSM peak of −4.3 J/kg·K with ΔTFWHM = 50 K for the second-order magnetic transition under μ0ΔH = 5.0 T was achieved. By employing both magnetizing and demagnetizing processes for magnetic cooling, the two successive inverse and conventional MCEs in Ni–Fe–Mn–Sn microwires may show potential applications for micro-devices and systems.

Magnetocaloric effect in bamboo-grained Ni-Mn-Ga microwires over a wide working temperature interval

Bamboo-grained Ni-Mn-Ga microwire is promising for achieving considerable magnetic-field-induced strain due to less neighboring grain constraints to the twin boundary motion. Such reduction of resistance to interface motion also favors the reduction of hysteresis in magnetic refrigeration. Here, bamboo-grained Ni-Mn-Ga microwires were successfully synthesized by a melt-extraction technique and subsequent high temperature heat treatment at 1323 K for 3 h under Argon atmosphere. Corresponding microstructure, martensite transformation (MT) behaviors and magnetocaloric properties were investigated. The high specific surface area of the microwires favored the element evaporation at high temperature, leading to a heterogeneous composition state, which is responsible for the MT temperature (range) change and the multi-variants state in the bamboo-grained microwires. Nearly no magnetic hysteresis loss was obtained. The increased compositional variation led to the partial overlap of the MT and the magnetic transition, resulting in the improvement of the working temperature interval ~71 K and net refrigeration capacity ~255 J/kg under μ0H = 5 T, which is heretofore the largest value reported in Ni-Mn-based Heusler alloys. When utilized as refrigerant in a cooling device, such small-sized microwires can increase the contacting area between the material and the heat-transfer agent, which helps the heat exchange and thus improve the refrigeration efficiency.

Core-shell ferromagnetic microwires extracted from PrDyFeCoB and GdPrDy(FeCo)B melts

The α-Fe core/PrDy-FeCo-B(48 at.%)α-Fe(52 at.%) shell and GdPrDy(FeCo)B microwires were grown by pendant drop melt (PDM) extraction technique. Single core–shell microwires of ~80–100 μm diameter and 2–20 mm length manifest rectangular hysteresis loops corresponding to ~100 Oe switching magnetic fields. Bistability of the microwires relates to single domain state of the α-Fe inner core revealed by scanning electron microscopy (SEM). Rare-earth amorphous PrDy-FeCo-B shell of the microwire scanned by magnetic force microscope (MFM) possesses magnetization reversal nuclei corresponding to the α-Fe inclusions. Interwire magnetic dipole interaction and scattering of microwire size change shape of the magnetic hysteresis loop and increase coercive field up to 983 Oe, in chaotic ensembles of the core–shell microwires. The GdPrDy(FeCo)B microwires of the same sizes with no Fe core possess “butterfly” type of the hysteresis loop of high coercivity ~20 kOe.

Martensitic transformation and superelasticity in Au7Cu5Al4 shape memory alloy microwires

The martensitic transformation and superelasticity of Au7Cu5Al4 shape memory alloy were investigated. Polycrystalline Au7Cu5Al4 microwires with a diameter of 20–120 μm were fabricated using a melt-extraction technique. The brittle failure of microwires with an oligocrystalline structure obtained by cyclic heat treatment was significantly suppressed. Such microwires exhibited a recoverable strain of 5.6% under 6.8% applied strain at 90 °C. Stable superelastic behavior with complete shape recovery was observed up to 119 °C under 1.8% applied strain.

Tunable Magnetocaloric Effect in Ni-Mn-Ga Microwires

Magnetic refrigeration is of great interest due to its high energy efficiency, environmental friendliness and low cost. However, undesired hysteresis losses, concentrated working temperature interval (WTI) and poor mechanical stability are vital drawbacks that hinder its practical application. Off-stoichiometric Ni-Mn-Ga Heusler alloys are capable of giant magnetocaloric effect (MCE) and tunable transformation temperatures. Here, by creating Ni-Mn-Ga microwires with diameter of 35–80 μm using a melt-extraction technique, negligible hysteresis and relatively good mechanical stability are found due to the high specific surface area (SSA) that reduces incompatibility between neighboring grains. The high SSA also favors the element evaporation at high temperatures so that the transformation temperatures can be feasibly adjusted. Tunable magnetocaloric effect owing to different magneto-structural coupling states is realized by (i) composition design and subsequent tuning, which adjusts the temperature difference between the martensite transformation (MT) and the magnetic transition, and (ii) creation of gradient composition distribution state, which manipulates the MT range. Magnetic entropy change ΔSm ~−18.5 J kg−1 K−1 with relatively concentrated WTI and WTI up to ~60 K with net refrigeration capacity ~240 J kg−1 at 50 kOe are demonstrated in the present Ni-Mn-Ga microwires. This criterion is also applicable for other small-sized materials.

Microstructure, mechanical and magnetic properties of melt extracted Fe-6.5 wt.%Si microwires

Fe-6.5wt.%Si microwires with 40∼100μm diameter and 2∼30cm length were successfully fabricated by the melt extraction technique. The microwires possess a D-shaped cross-section and exhibit high ductility at room temperature due to rapid solidification inhibiting the formation of ordered phases. The fan-like microstructure, which forms as a result of a fan-like temperature gradient, consists of equiaxed crystals in the centre and columnar crystals along the radial direction. Significant dependence of magnetic moment on the sample spatial orientation with respect to the magnetic field has been observed from M-θ curves, which exhibit a “W” shape from 50Oe to 7000Oe due to shape anisotropy effects and a “Double-W” shape from 8000Oe to 10000Oe due to a compromise between the demagnetizing field energy (Ed) and external field (Zeeman) energy (Eh).

High damping capacity of Ni–Mn–Ga–Cu microwires prepared by melt-extraction technique

Ni–Mn–Ga–Cu microwires, with diameter of 20–80 μm, length of 30–150 mm and fined columnar grains, were produced by melt-extraction technique. The damping capacity of the extracted microwires was investigated by stretching a microwire under a tensile stress using dynamic mechanical analyzer. The damping capacity of the martensite and austenite phases shows a weak frequency dependence but a strong strain amplitude dependence. The damping capacity (Tanδ) of the martensite and austenite phases reaches 0.08 and 0.04, respectively, under strain amplitude of 0.5% and frequency of 1 Hz. The high damping capacity of the martensite phase is related to the high mobility of martensite twin boudaries, while that of austenite phase to the motion of dislocations. The ferromagnetic Ni–Mn–Ga–Cu microwires, with high ductility and damping capacity, may act as promising materials for microscale devices, systems and composite fillers for passive dissipation of undesired vibrations and noises.

Cooling rate-dependent yield behavior of metallic glass wires

The current work presents an exhaustively study on cooling rate-dependent yield behavior of Cu50Zr50 (at%) and Ni56Nb44metallic glass (MG) wires fabricated by a melt-extraction technique. After tension test, based on the measurement of the fracture angle, the yield behavior of the MG wires with different diameters is analyzed. Based on the Mohr-Columb criterion, the cohesion strength of the MG wires is evaluated. According to the free volume model, the cohesion strength of the MG wires is quantitatively predicted. The correlation between the yield behavior and the quantity of free volume in the glassy phase is elucidated.

Tensile Strength Reliability Analysis of Cu48Zr48Al4 Amorphous Microwires

Uniform Cu48Zr48Al4 amorphous microwires with a high surface quality are fabricated by a melt extraction technique. The mechanical property of microwires is evaluated via tensile tests. To estimate the strength scattering, statistical analysis of fracture strengths is conducted using logarithmic normal distribution, and two- and three-parameter Weibull analysis, severally. The results show that the tensile strengths of Cu48Zr48Al4 amorphous microwires range from 1724 to 1937 MPa with the arithmetical average value of 1836 MPa, and the arithmetical standard deviation of 56.4 MPa. The geometric mean of fracture strength is 1840 MPa using logarithmic normal distribution statistical analysis. Using two- and three-parameter Weibull analysis, the Weibull modulus and fracture threshold value are respectively calculated for 34.8 and 1483 MPa, which shows the excellent tensile mechanical properties with a high predictability of Cu48Zr48Al4 amorphous microwires and further indicates the great potential of application.

Magnetocaloric effect of Ni-Fe-Mn-Sn microwires prepared by melt-extraction technique

Small-sized materials with large surface to volume ratio favor heat transfer during magnetic refrigeration cycling and thus may help enhancing the refrigeration efficiency. Here, high Fe content Ni44.9Fe4.3Mn38.3Sn12.5 polycrystalline microwires were prepared by a melt-extraction technique. The as-extracted microwires were annealed at 1173K for 60min, leading to significant grain growth and formation of a secondary Fe-rich γ phase. The annealed microwire exhibits larger magnetization difference (ΔM) between the austenite and martensite phases and smaller thermal hysteresis compared to the as-extracted microwire. The annealed microwire possesses a magnetic transition to austenite at 299K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208K upon cooling. Under a magnetic field of 50kOe, the annealed microwires show a maximum magnetic entropy change ΔSm of 6.9J/kg·K and an effective refrigeration capacity RCeff of 78.0J/kg over a broad working temperature span ΔTFWHM of 20K around the MT. In addition, magnetic transition of the austenite gives rise to ΔSm −3.7J/kg·K and RCmag 232.5J/kg with ΔTFWHM of 85K under 50kOe.

Influence of Oxygen on the Fatigue Behaviour of Ti-6Al-7Nb Alloy

One of the challenges in PM Ti alloys is to control the impurities level. Oxygen affects the microstructure and the mechanical properties of titanium alloys. Ti-6Al-7Nb is a promising alloy to use in PM due to its outstanding biocompatibility and mechanical properties required for load bearing medical implants. In this work, the influence of the impurities content on the ductility, fatigue resistance and microstructure of Ti-6Al-7Nb alloy processed by metal injection moulding was examined. Tensile and fatigue specimens were manufactured using Ti-6Al-7Nb gas atomized powder. Depending on the thermal treatment time, various oxygen contents were introduced into the specimens. The resulting oxygen content was determined by melt extraction technique. Tensile tests and high cycle four-point bending fatigue tests at room temperature were performed. First studies about the effect of oxygen content on crack initiation and propagation were done by the observation of microstructures and fractured surfaces using light and electron microscopy (SEM).

Metal Injection Moulding of Ti-6Al-4V with Yttrium Addition

For highly loaded parts, such as medical implants as well as for engineering application, high strength and good ductility are indispensable, but also the fatigue resistance plays an important role. For both, quasi static and fatigue properties, a fine microstructure is essential. Furthermore, especially for titanium alloys the control of interstitial impurities like oxygen and nitrogen is very important. In a former study additions of several oxides of rare earth elements were tested with respect to their effect on the microstructure of MIM processed Ti-6Al-4V. Yttrium oxide has shown the strongest effect on the colony size of Ti-6Al-4V.In this study elementary yttrium powder was added to Ti-6Al-4V. During sintering, the yttrium scavenges oxygen out of the titanium matrix, increasing the ductility. The yttrium oxide, which is formed, leads to a colony refinement and therefore to a higher strength.For preliminary tests cylindrical samples consisting of Ti-6Al-4V powder blended with coarse yttrium powder and a wax and polyethylene-based binder were manufactured by uniaxial pressing and sintering. The addition of yttrium led to a slight decrease of the colony size: specimens sintered at a high temperature of 1400 °C show a stronger dependency of yttrium content on the colony size than those sintered at 1300 °C.Tensile test specimens were produced by MIM using gas atomized Ti-6Al-4V-powder with additions of yttrium powder between 0.1 and 0.5 wt.-%. Sintering took place at temperatures between 1300 °C and 1400 °C with two different dwell times (2 and 4 hours). Tensile tests were conducted in air at room temperature. The microstructures were observed by SEM and light optical microscope. Oxygen and nitrogen contents were analysed by a melt extraction technique.