Working Temperature Interval Research Articles

Microstructure and magnetocaloric effect in nonequilibrium solidified Ni-Mn-Sn-Co alloy prepared by laser powder bed fusion

Additive manufacturing (AM) enables complex structures of Ni-Mn-X Heusler alloys to be utilized in solid state refrigeration systems. Here, the laser powder bed fusion (L-PBF) technique was used to fabricate a Ni-Mn-Sn-Co magnetic shape memory alloy with sophisticated geometries. Relative densities ranging from 96.12 to 97.04% were attained. L21–ordered austenite and an average structure of 5-layered modulated (5 M) martensite were observed at ambient temperature. The nonequilibrium solidification condition and repeated remelting processes during L-PBF gave rise to a strong 〈001〉A texture in austenite with epitaxial columnar grains along the build direction and dendrites related to microsegregation. Furthermore, the austenite exhibited nanodomains in its matrix and the martensite possessed stacking-mediated structures with 4–7 layers of atoms randomly stacked within the twin substructures. The combined influence of relatively homogeneous composition and specific microstructures yielded a competitive magnetization difference of 81.0 A·m2·kg–1 and a maximum magnetic entropy change of about 14 J·kg–1·K–1 with a working temperature interval of about 22 K under the external field change of 5.0 T without any heat treatment. The as-built state alloy is expected to facilitate the development of new laser AM techniques for Ni-Mn-X alloys.

Enhancing magnetocaloric properties of NiMnGa-based alloys via Dy micro-alloying and pseudoelastic cyclic training

Considerable interest to improve magnetic entropy change (ΔSm) and broaden working temperature interval (WTI) of NiMnGa ferromagnetic shape memory alloys (FESMAs) was stimulated by their applications as promising candidate materials for solid-state refrigeration. In the present study, we presented an approach to enhance the magnetocaloric properties of polycrystalline NiMnGa FESMAs via combining Dy micro-alloying and pseudoelastic cyclic training. The introduction of Dy elements established stable magneto-structural coupling transformation from the paramagnetic austenite to ferromagnetic martensite, accompanied by a large ΔSm [−16.42 J/(kg K)] and a widened WTI (∼15.98 K). Fascinatingly, it was demonstrated that the internal strain fields at phase interface between matrix and DyNi4Ga precipitates could assist the phase transformation nucleation, which significantly reduced the hysteresis loss from 20.84 J/kg of Ni54Mn25Ga21 alloy to 8.14 J/kg of Ni54Mn25Ga20.7Dy0.3 alloy. More importantly, the subsequent pseudoelastic cyclic training produced a strong ⟨110⟩NM preferred crystallographic orientation, which facilitated the magnetic alignment along easy magnetization axis. Consequently, the giant ΔSm value up to −24.25 J/(kg K) and effective refrigeration capacity RCeff of 198.77 J/kg were further achieved in the trained Ni54Mn25Ga20.7Dy0.3 alloy under an external magnetic-field change of 5.0 T.

ЭПОКСИДНЫЕ АНТИФРИКЦИОННЫЕ ПОКРЫТИЯ, НАПОЛНЕННЫЕ ОБРАБОТАННОЙ ПОВЕРХНОСТНО-АКТИВНЫМИ ВЕЩЕСТВАМИ ЗОЛОЙ РИСОВОЙ ШЕЛУХИ

The use of epoxy antifriction coatings can significantly reduce thermal stress in the friction zone and expand the coating working temperature interval while keeping high wear resistance. The paper considers the effect of non-activated and activated by surfactants silicate filler – rice husk ash on the physicochemical and mechanical properties of epoxy materials applied as antifriction coatings. All studied samples of rice husk ash, both initial and activated with surfactants, have an alkaline surface nature. The study identified that all cationic quaternary ammonium salts (QAS) reduce the pH of rice husk ash. At the same time, nonionic OXIPAV increases this indicator. Activation of the rice husk ash surface, both by the quaternary ammonium salts and aminosilanes, significantly reduces the porosity of this silicate. In this case, the average pore diameter does not change significantly, and their specific surface area decreases significantly, to a lesser extent, when activated by nonionic quaternary ammonium salts. The application of quaternary ammonium salts and aminosilanes in the amount of 33 % for activation of the surface of the investigated silicate filler reduces its modifying effect in epoxy compositions, regardless of the chemical structure of the surfactants used, which is not a typical effect. Therefore, the authors assumed that the suboptimal concentration of quaternary ammonium salts and aminosilanes was used. The study identified that the optimal concentration of 50 % alcohol solution of KATAPAV is 14.7–21 %. In this range of the QAS content, there is a significant increase in hardness (about 40 %), a slight decrease in wear (about 10 %), and a significant decrease in the coefficient of static friction (up to 2 times). At the same time, the authors observed an increase in adhesion to metal up to 3 times and bending strength up to 25 %. Thus, rice husk ash activated with an optimal amount of quaternary ammonium salts is an effective modifier of epoxy coatings, which improves their antifriction properties and increases wear resistance, hardness, strength, and adhesion characteristics.

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.

Investigating the microstructure and magnetic properties of La-Fe-Si microwires during fabrication and heat treatment process

In this study, the optimized fabrication and evolution of the microstructure and magnetic transition behavior of the melt-extraction LaFe11.2Si1.8 microwires have been studied. After the optimization of extraction technique (heating power 22 KW, feeding rate 30–50 μm/s, rotation velocity 1700 r/min), the content of La(Fe,Si)13 phase in the as-extracted microwires was 54 wt% due to the high solidification velocity, which was increased to 85 wt% via annealing at 1373 K for 20 min. The amount of La(Fe,Si)13 phase was increased and the composition of La(Fe,Si)13 phase became more homogenized through peritectic reaction and short-distance diffusion in the microwires during annealing process. The coexistence of the nanocrystalline and amorphous structures contributed to the broad magnetic transition temperature range of the as-extracted and annealed microwires. The annealed microwires exhibited a second-order magnetic transformation behavior and showed a maximum magnetic entropy change |ΔSM|max of 6.2 J/kg·K and working temperature interval of 36.0 K under a magnetic field of 20 kOe.

Elastocaloric effect with small hysteresis in bamboo-grained Cu–Al–Mn microwires

The elastocaloric effect in Cu–Al–Mn shape memory alloy microwires fabricated by Taylor–Ulitovsky method was investigated. The microwires with bamboo-like grain architecture, homogeneous composition and favorable orientation were successfully prepared through high-temperature annealing heat treatment. The formation of the bamboo grains and high specific surface area contribute to the reduced martensite transformation hysteresis. A large recoverable strain up to 8.8% was achieved by two-way shape memory cycling under a low stress of 50 MPa. Consequently, the microwire exhibited a large entropy change ΔSiso = 16.1 J kg−1 K−1. Furthermore, the refrigeration capacity (RC) reached ~ 502 J kg−1 over a working temperature interval ΔTFWHM = 31 K during direct transformation under 50 MPa uniaxial stress. Finally, a reversible adiabatic temperature change ΔTad = 3.9 K under a stress of 150 MPa was obtained. This proves that the present Cu–Al–Mn microwire, with bamboo grains, high refrigeration property and low cost, may act as promising candidate materials for elastocaloric cooling.

Heat Generation Characteristic of High Power Charging for BEV

With the increasing of the long range of electric vehicles, the high power charging technology over 250 kw is urgently needed to reduce the charging time and improve the convenience of using. However, high power charging is more obvious about generating heat than conventional power, which will affect the battery's charging efficiency, cycle life, and possibly even safety risks. Aiming at the above problems, two typical LiFePO4(LFP) and Li(NiCoMn)O2(NCM) batteries were selected to study the heat production characteristics of energy-based power cells with large power charging based on model and experiment. It is found that the maximum charging capacity of high power charging is greatly affected by the heat management system. Under the condition of forced-air cooling with over 4c-rate charging, the battery heat generation can make battery temperature over 55 degrees, but the water-cooled heat management system can make the battery work in the rated working temperature interval. Under the condition of more than 3c-rate charging, the model's parameter mismatch is serious and the temperature difference between inside and outside is needed to be correction to applied to the high power charging strategy of electric vehicle on line.

Effect of partial metamagnetic and magnetic transition coupling on the magnetocaloric effect of Ni-Mn-Sn-Fe alloy

For Ni-Mn-Z based (Z = Sn, In, Sb) alloys, the martensite transformation (MT) and magnetic transition in austenite state create opposite magnetic cooling effect, which offsets each other when the first-order MT (FOMT) coincides with the second-order magnetic transition (SOMT). In the present study, two successive magnetization peaks are introduced in a Ni48.4Fe1.1Mn38.5Sn12.0 alloy by creation of a partial overlap between reverse MT and magnetic transition in the austenite phase with 1.1 at.% Fe-doping. In addition, significant enhancement of the magnetization difference (ΔM) between martensite/austenite phases is achieved. Consequently, an inverse magnetocaloric effect (IMCE) associated with a positive isothermal magnetic entropy change (ΔSM) of 9.6 J/kg∙K and a working temperature interval (ΔTFWHM) of 306–314 K is found under an external magnetic field of 5.0 T in the reverse MT and TCA temperature range. This IMCE is followed by a conventional magnetocaloric effect (CMCE) with a negative ΔSM of −2.7 J/kg∙K and ΔTFWHM of 316–339 K under 5.0 T. By taking advantage of these two successive MCEs using a special designed device, large caloric cooling effect with enhanced working temperature interval may be of interesting for practical room-temperature refrigeration applications.

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.

Enhanced magnetic refrigeration capacity in Ni-Mn-Ga micro-particles

Bulk magnetic refrigerant materials with first-order character usually possess hysteresis losses and concentrated refrigeration working temperature interval (δTFWHM), which are detrimental for magnetic refrigeration applications. Here, we report on Ni-Mn-Ga micro-particles with size ~38.5–45μm fabricated by grinding and subsequent stress relief annealing (SRA). The microstructure, martensite transformation (MT), hysteresis loss and magnetocaloric effect (MCE) of the SRA particles were studied in comparison with the bulk alloy counterpart. The thermal and magnetic hysteresis losses in SRA particles ~1.3K and ~1.9J/kg were significantly reduced compared to those in the bulk alloy ~5.5K and ~9.7J/kg, respectively, which is related to the reduction of neighboring grain constraints on martensite/austenite phase boundary motion. The MT transformation temperature range of the SRA particles ~26.5K was higher than that of the bulk alloy ~5.5K because of the high specific surface area of the particles and the residual internal stress after SRA. A magneto-structural partly-coupled state was attained in the SRA particles, which is responsible for the wide δTFWHM ~25K and the high refrigeration capacity (RCnet) ~117J/kg. Based on these results, a possible approach for the high magnetic refrigeration efficiency is expected and discussed.

Effect of Si doping on microstructure and martensite transformation in Ni-Mn-Sb ferromagnetic shape memory alloys

We have recently reported that the quaternary Ni49.0Mn38.4Sb11.7Si0.9 alloy showed enhanced refrigeration capacity due to the wide working temperature interval and narrow magnetic hysteresis loss via Si-doping. Here we systematically investigate the microstructure, martensite transformation and magnetic transition behaviors of Ni50Mn38Sb12-xSix (x = 0, 1, 2, 3) alloys. Ni50Mn38Sb12-xSix (x = 0, 1, 2) alloys exhibited a full solid-solution state with a four-layer modulated orthorhombic (4O) martensite structure. However, three phases formed in Ni50Mn38Sb9Si3 alloy, and lath-like martensite twins existed only in α phase at room temperature. The martensite transformation temperature decreased with the increasing Si content when the Si atomic content increased from 0% to 2%, but significantly increased when Si content reached to 3% because of the increase of the valence electron concentration (e/a) of matrix phase (α phase). The martensitic transformation also occurred in the β phase below room temperature in Ni50Mn38Sb9Si3 alloy. Furthermore, the martensite transformation temperature range enlarged and the thermal hysteresis narrowed with the addition of Si atomic content from 0% to 2%, of which Ni50Mn38Sb10Si2 alloy had the widest martensite transformation temperature range and narrowest thermal hysteresis, which was supposed to have great magnetocaloric effect (MCE). However, when x = 3, the thermal hysteresis increased significantly and the transition character changed to a second-order phase transition above room temperature; a magneto-structural coupling of the first-order martensitic transformation and second-order magnetic transition also existed below room temperature, which all would result in low MCE.

Enhanced magnetocaloric effects of Ni-Fe-Mn-Sn alloys involving strong metamagnetic behavior

Very recently, we reported that Fe-doped Ni50-xFexMn38.0Sn12.0 alloys exhibited enhanced magnetization difference ΔM between the martensite and austenite phases. Of note is that the alloy with x = 4.2 exhibits a strong metamagnetic transition behavior, i.e. magnetic-field-induced reverse martensite transformation, which is favorable for the magnetocaloric effects. Here, the enhanced magnetocaloric effect related to metamagnetic transition in the selected Ni35.8Fe4.2Mn38.0Sn12.0 alloy was reported. This alloy exhibits a high magnetization difference ΔM of ∼58 A·m2/kg between martensite and austenite phases owing to the magnetic and structural coupling. The doping of Fe leads to a strong metamagnetic behavior, with austenite peak temperature shift ΔAp/ΔH reaching −2.4 K/T. As a result, the magnetic entropy change ΔSm increases rapidly from a starting critical magnetic field ∼0.2 T and then saturates at various finishing critical magnetic fields, depending on the working temperature. A sizable peak ΔSm of 33.8 J/kg·K with a working temperature interval of 7 K is obtained under a magnetic field of 5 T, which is responsible for a high relative cooling power RCP of 237 J/kg. These results suggest that Ni45.8Fe4.2Mn38.0Sn12.0 alloy may act as a potential solid-state magnetic refrigerant.

Thermal Lens Temperature Scanning technique for evaluation of oxidative stability and time of transesterification during biodiesel synthesis

In this work, laser-induced Thermal Lens Temperature Scanning technique (TL-TS) is applied to evaluate oxidative stability and time of transesterification during biodiesel synthesis. Samples collected at different time intervals during the transesterification process of sunflower (SF) and soybean (SB) oils were submitted to fast oxidation through temperature scanning (between 22 and 190°C), and simultaneously measured with the TL-TS technique. Temperature dependence of Thermal Lens effect amplitude showed the occurrence of oxidation, with the onset (Tonset) changing with the transesterification stages from 149 to 169°C for sunflower and from 120 to 142°C for soybean samples. The characteristic evolution of Tonset with reaction duration was estimated to be ∼7min for sunflower and ∼10min for soybean samples. The thermal diffusivity values were shown to be sensitive to rapid changes at transition temperatures, which could be related to molecular ruptures. Additional measurements were performed with DSC, TG and FTIR, to validate the information obtained by the TL-TS technique. In conclusion, the results showed the TL-TS technique as a promising tool for oxidative stability evaluation and determination of both chosen working temperature and minimal time interval for the solution to reach an optimized transesterification stage, thus contributing for reduction of costs, quality control and consequently for certification of biodiesel fuels.

Magnetocaloric effect with low magnetic hysteresis loss in ferromagnetic Ni-Mn-Sb-Si alloys

Giant magnetocaloric effect in Ni-Mn-X (X=In, Sn, Sb) Heusler alloys has been revealed due to the significant shift of the martensite transformation temperatures under a bias magnetic field. However, the magnetic hysteresis during the magnetization and demagnetization cycles creates a large hysteresis loss and reduces the refrigeration capacity. Here we demonstrated that the magnetic hysteresis loss in Ni-Mn-Sb alloys was effectively reduced by Si-doping. The quaternary Ni49.0Mn38.4Sb11.7Si0.9 alloy exhibited martensite and magnetic transitions around room temperature. Maximum magnetic entropy change ΔSm 9.4J/kgK and working temperature interval 7.0K were achieved attributed to the martensite transformation under a magnetic field of 5T. Meanwhile, the average magnetic hysteresis loss for Ni49.0Mn38.4Sb11.7Si0.9 alloy was 2.1J/kg, much smaller than that for Ni49.0Mn38.5Sb12.5 alloy, 11.4J/kg. As a result, a refrigeration capacity of 50.2J/kg was obtained in the Ni49.0Mn38.4Sb11.7Si0.9 alloy. This result shows that Si-doped Ni-Mn-Sb alloys may act as a potential material system for magnetic refrigeration.

Martensite transformation and magnetic properties of Fe-doped Ni-Mn-Sn alloys with dual phases

Ni-Mn-Sn alloys exhibit high magnetocaloric effect (MCE) during the magnetic-field-induced martensite to austenite phase transformation. However, the low magnetization of the austenite, narrow working temperature interval and high magnetic hysteresis reduced their magnetic refrigeration capacity. Here, the effects of Fe doping on the structural and magnetic transitions of Ni50-xFexMn38Sn12 alloys were investigated. The doping of Fe higher than 2.9% induced the occurrence of a secondary γ phase, creating a dual phase alloy. The martensite transformation temperature significantly decreased with the occurrence of the secondary phase. However, the Curie temperatures of both austenite and martensite changed slightly with the formation of the secondary phase. As a result, the magnetostructural coupling, i.e. overlap of the structural and magnetic transitions between the ferromagnetic austenite and the paramagnetic martensite, occurred in the alloys with x = 0.5 - ∼4.2. Furthermore, the magnetization of the austenite and martensite both increased with increasing Fe content from x = 0 to x = 5.5, with the magnetization difference between the austenite and martensite saturating at x = 4.2. The dual phase Ni45.8Fe4.2Mn38Sn12 alloy, exhibiting a magnetic field dependence of martensite transformation temperature ΔTM/μΔH - 0.28 K/kOe, showed a wider working temperature interval than that of the un-doped Ni50Mn38Sn12 alloy. This demonstrated that the Ni45.8Fe4.2Mn38Sn12 alloy might exhibit a high magnetic entropy change, wide working temperature interval and low magnetic hysteresis, and thus may be a promising magnetic refrigeration material.

Enhanced magnetocaloric effect in a Co-doped Heusler Mn50Ni37Co3In10 unidirectional crystal

A high-pressure optical zone-melting technique was employed to grow a Mn-rich Heusler Mn50Ni37Co3In10 unidirectional crystal in the present study. It was found that the Co-doped Mn50Ni37Co3In10 unidirectional crystal showed a low magnetic hysteretic loss and a widened working temperature interval in the vicinity of the martensitic transformation. The inverse magnetic entropy change (∆SM) reached 7.84Jkg−1K−1 around 237.5K under a magnetic field change of 30kOe, and the corresponding effective refrigeration capacity (RCeff) was about 127.2Jkg−1. The experimental results demonstrated a high potential to develop high-performance Mn-rich Heusler Mn–Ni–In magnetocaloric materials by means of Co doping in combination with the high-pressure optical zone-melting fabrication technique.

Magnetostructural coupling and magnetocaloric effect in Ni-Mn-Ga-Cu microwires

Ni-Mn-Ga-X microwires were produced by melt-extraction technique on a large scale. Their shape memory effect, superelasticity, and damping capacity have been demonstrated. Here, the excellent magnetocaloric effect was revealed in Ni-Mn-Ga-Cu microwires produced by melt-extraction and subsequent annealing. The overlap of the martensitic and magnetic transformations, i.e., magnetostructural coupling, was achieved in the annealed microwires. The magnetostructural coupling and wide martensitic transformation temperature range contribute to a large magnetic entropy change of −8.3 J/kg K with a wide working temperature interval of ∼13 K under a magnetic field of 50 kOe. Accordingly, a high refrigeration capacity of ∼78 J/kg was produced in the annealed microwires.

Enhanced magnetic entropy change and working temperature interval in Ni–Mn–In–Co alloys

High magnetic entropy change and wide working temperature interval are both of great importance for the application of magnetic refrigerant working materials. Here Ni–Mn–In–Co alloys with oligocrystalline structure were produced by annealing heat treatment and the giant magnetocaloric effect and large working temperature interval were confirmed. The annealing increases the magnetization difference ΔM between martensite and austenite. The annealed alloy subjects to a reverse martensite to austenite and an intermediate phase transformation upon heating. The two-stage field-induced reverse transformation, contribute to a maximum magnetic entropy change of 37.1 J/kgK at 309 K under a magnetic field of 50000 Oe, were observed for the first time. In addition, a broadened working temperature interval of ∼22 K was obtained owing to the intermediate phase transformation. The giant room-temperature MCE in quaternary Ni–Mn–In–Co alloys is promising for magnetic refrigeration.

The Structure and Physical-Mechanical Properties of Multicomponent Porous TiNi (Mo, Fe, Cu) Alloys

The copper alloying effect on the special features and physical-mechanical properties of multicomponent porous TiNi- base alloys has been investigated. A partial replacement of Ni by 1I 10 at.% Cu in a porous TiNibase alloy is shown to produce changes in the phase composition of the material and to give rise to dendritic regions. The behavior of each of the materials under study with addition of Cu as an alloying element depends on the size and distribution density of precipitate particles and dendrites. The change in the structural state of porous TiNi-base alloys with Cu additions due to Ti- and Ni-rich phase precipitation and formation of dendritic regions is found to bring about changes in the physical-mechanical properties of the materials over a wide temperature interval. Optimum copper concentrations were fixed to be in the range from 3 to 6 at.%. With these concentrations, the porous alloys of the above-indicated composition exhibited a wide working temperature interval (0I 40°C) over which reversible deformation developed and martensite shear stresses were of very low magnitudes.

The study of the magnetic and room-temperature magnetocaloric properties in spin-reorientation Nd 1− xDy xCo 4Al ( x = 0, 0.1) alloys

The spin-reorientation and magnetocaloric property in Nd 1− x Dy x Co 4Al ( x = 0, 0.1) alloys are investigated. These alloys undergo two successive spin-reorientation transitions around room-temperature, which results in a positive and negative magnetic entropy change, respectively. With the increasing applied field (<30 kOe), these spin-reorientation alloys show wide working temperature interval and relatively large values of refrigerant capacity. The spin-reorientation material would be a promising candidate for room-temperature magnetic refrigerant.