Study of the Microstructure, Mechanical, and Magnetic Properties of

materials Article

Study of the Microstructure, Mechanical, and Magnetic Properties of LaFe11.6Si1.4Hy/Bi Magnetocaloric Composites Zhengang Liu 1,2 1

2 3

*

ID

, Qiming Wu 1 , Naikun Sun 3 , Zan Ding 1 and Lingwei Li 1,2, *

Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China; [email protected] (Z.L.); [email protected] (Q.W.); [email protected] (Z.D.) Institute of Materials Physics and Chemistry, School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China School of Science, Shenyang Ligong University, Shenyang 110159, China; [email protected] Correspondence: [email protected]

Received: 10 May 2018; Accepted: 1 June 2018; Published: 4 June 2018







Abstract: We have successfully synthesized LaFe11.6 Si1.4 Hy /Bi composites by cold pressing together with vacuum annealing technology, and systematically investigated the microstructure, magnetism, mechanical performance, and magnetocaloric properties. LaFe11.6 Si1.4 Hy particles are well surrounded by metallic Bi, without the formation of new phase. The maximum values of the volumetric magnetic entropy change -∆SM are as high as 51, 49, and 35 mJ/cm3 K around 263 K, for the composites with 5, 10 and 15 wt % Bi contents, respectively. The maximum value of the compressive strength for LaFe11.6 Si1.4 Hy /Bi composites increased continuously from 155 to 358 MPa with increasing Bi content, from 0 to 15 wt %. Keywords: mechanical properties; magnetocaloric effect; LaFe11.6Si1.4Hy/Bi composites; magnetic properties

1. Introduction Magnetic refrigeration based on the magnetocaloric effect (MCE) has been considered as a new type of refrigeration system, which is environmentally friendly, energy-saving and highly efficient [1]. It is of great importance to examine materials with a large MCE that may work at different temperature ranges, especially for around room temperature [1–26]. Early studies indicated that high-purity Gd shows considerable MCE near room temperature, with nice mechanical properties [11,12]. However, its application is limited by its non-adjustable Curie temperature (TC ) and high price. In order to find materials which are more favorable than pure Gd, many room temperature magnetocaloric materials have been studied, including Gd-Si-Ge, La-Fe-Si, and MnAs-based alloys [13–15]. One of the most promising room temperature magnetic refrigerants is La(Fex Si1−x )13 hydride [11]. However, the inherent brittleness and hydrogen cracking of the 1:13 phase during the hydrogenation break the hydrides into powder, which is not in conformity with the requirements of shape for use in magnetocaloric regenerators [9,10,16]. Lyubina et al. obtained porous La(Fe,Si)13 materials by hot pressed (HP) La-Fe-Si particles which exhibited better mechanical properties and lower hysteresis compared with bulk materials [10]. However, when the temperature is higher than 500 ◦ C, the precipitation of the second phase α-Fe decreases the MCE. On the other hand, the temperature of HP exceeds the dehydrogenation temperature of La(Fe,Si)13 hydrides. La(Fex Si1−x )13 Hy used in refrigeration equipment should have both a large MCE working temperature near room temperature, great mechanical properties, and higher thermal conductivity [17]. Nevertheless,

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La(Fex Si1−x )13 Hy powder could be greatly improvemed, in terms of its mechanical properties, by polymer bonding [18–21]. Heat exchangers made of polymer bonded composites combine the magnetocaloric properties of La(Fe,Mn,Si)13 Hx loose powders with better mechanical and chemical stabilities. A major disadvantage of using polymeric binders to consolidate magnetocaloric alloy powders is the low thermal conductivity of composites. High thermal conductivity is a prerequisite for ensuring that magnetocaloric materials can be used. Compared with polymer bonding, methods that use a metal or alloy as a binder yield better mechanical properties and thermal conductivities [22–24]. If the mixed powder is compressed at low temperature, the formation of α-Fe could be avoided. Therefore, a good binder for the compression molding of La(Fe,Si)13 Hy powder should have high thermal conductivity and a low softening point/melting point. Although Zhang et al. prepared a LaFe11.6 Si1.4 Hy /Sn composite which demonstrated good magnetocaloric and mechanical properties compared with others [25], it should be considered that the phase transition of Sn near 286 K reduces the mechanical stability of the composite [26], which is very unfavorable for practical use. Therefore, we chose metallic Bi as a binder, and investigated the mechanical and magnetocaloric performance of LaFe11.6 Si1.4 Hy /Bi composites. 2. Materials and Methods The LaFe11.6 Si1.4 alloy was prepared by arc melting, and then annealed in a vacuum at 1050 ◦ C for 7 days. The annealed samples were quenched in water, and then milled. The ingots were broken and ground into powders, and the powder with particle sizes of 50–75 µm was selected by sieving, and then annealed at 423 K for 2 h with H2 at a pressure of 2 MPa. The hydrogen concentration of LaFe11.6 Si1.4 Hy was determined to be ~1.4 by weighing the powder before and after hydrogenation. Commercial Bi powder with the size of 10–20 µm was selected, and the LaFe11.6 Si1.4 H1.4 powder was uniformly mixed with metallic Bi powder as a binder. The mass ratio of the Bi powder in the mixed powder was 5, 10, and 15%. The mixed powder was pressed under a pressure of 1625 MPa for 10 min. The mixture was annealed inside a stainless mold (without pressure) in a vacuum at 300 ◦ C for 10 min, followed subsequently demolding at room temperature. A cylindrical sample of φ5 × 2.7 mm was then obtained. X-ray diffraction (XRD) (Rigaku RINT 2200 diffractometer, Malvern Panalytical, Almelo, The Netherlands) was employed to examine the phase and crystal structure. The microstructure of the material was studied using a Scanning Electron microscope (SEM) (Fesm, Zeiss & Ultra Plus, Carl Zeiss AG, Oberkochen, Germany). A compression test was performed at ambient temperature using an electronic universal testing machine (AG-Xplus100kN, Shimadzu, Kyoto, Japan) with a loading rate of 1.6 µm/s. Magnetic properties were measured using a commercially available vibrating sample magnetometer (VSM, Lakeshore, Carson, CA, USA), which was added at a high field measurement system (HFMS-9, Cryogenic, London, UK). The density of the sample was measured by the Archimedes method. 3. Results and Discussion The phase composition and microstructure for all the LaFe11.6 Si1.4 Hy /Bi composites were checked by XRD and SEM; all samples showed similar behavior. The room temperature XRD patterns and SEM images for 10 wt % metallic Bi-bonded LaFe11.6 Si1.4 Hy sample are given in Figure 1 as an example. The crystal structure includes the main phase NaZn13 (1:13 phase) and the secondary phase α-Fe in the matrix, in addition to the Bi phase of the binder. Compared with the lattice structure analysis of LaFe11.6 Si1.4 H1.4 and LaFe11.6 Si1.4 matrix, no new phase was formed between the matrix and Bi in the final composites. The content of the secondary phase α-Fe was the same as that of the matrix. From the XRD analysis results by the Maud software, the lattice constants of the LaFe11.6 Si1.4 alloy and its hydride and powder bonded sample were 1.143(2), 1.148(3), and 1.146(2), respectively, which is consistent well previously reported results [17]. This result shows that the lattice constants and unit cells volume of the hydride and bonded samples were increased. This is due to the hydrogen atoms entering the interstitial sites of the crystal lattice, which caused the lattice to expand. After processing,

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some of the H atoms overflow. Figure 2 show the SEM images; the gray phase is the LaFe11.6 Si1.4 Hy Materials 2018, 11, x FOR PEER REVIEW 3 of 7 Materials 11, x FOR REVIEW Bi, and the black area is the pores and cracks in the3 material. of 7 particle, the2018, white areaPEER is metallic LaFe11.6 Si1.4 in Hythe particles areLaFe bonded together byare metallic By holding the temperature above cracks material. 11.6Si1.4H y particles bondedBi. together by metallic Bi. By holding the the cracks in the material. LaFe11.6Si1.4Hy particles are bonded together by metallic Bi. By holding the melting point of Bi, most the pores are theofmetallic then forms chains. to the temperature above theofmelting point offilled; Bi, most the poresBiare filled; the metal metallic Bi thenDue forms temperature above the melting point of Bi, most of the pores are filled; the metallic Bi then forms metalofchains. Due toand thediffusion limitation distance, of Bi content and diffusion distance, some pores remained. limitation Bi content some pores remained. It should be noted that Itsome metal chains. Due to the limitation of Bi content and diffusion distance, some pores remained. It should be noted that some micro-cracks can be found on the surface of LaFe 11.6Siis 1.4H y particles, which by micro-cracks bethat found onmicro-cracks the surfacecan of LaFe Hysurface particles, which probably induced 11.6 Si should becan noted some be found on1.4the of LaFe 11.6Si1.4Hy particles, which is probably induced by the larger pressing pressure. the larger pressing pressure. is probably induced by the larger pressing pressure.

1. Powder XRD patterns for 11.6 LaFe , LaFe 11.6 1.4H LaFe 11.6Si 1.4H /BiHsamples. Figure 1.Figure Powder XRD patterns for LaFe Si11.6 , 1.4 LaFe SiSi1.4 H1.4 alloyand and LaFe Siy1.4 y /Bi samples. 1.4Si 11.6 1.4alloy 11.6 Figure 1. Powder XRD patterns for LaFe11.6Si1.4, LaFe11.6Si1.4H1.4 alloy and LaFe11.6Si1.4Hy/Bi samples.

crack crack

crack crack

La-Fe-Si-H La-Fe-Si-H Bi Bi pore pore

Bi Bi

2. SEM images for LaFe Hyy/Bi /Bi composite with 10 10 wt wt % metallic Bi. Bi. FigureFigure 2. SEM images for LaFe SiSi composite with % metallic 11.611.6 1.41.4H Figure 2. SEM images for LaFe11.6Si1.4Hy/Bi composite with 10 wt % metallic Bi.

For LaFe11.6Si1.4Hy/Bi bulk composites, apparent density increases with increasing metallic Bi

For LaFe 11.6SiH H/Bi y/Bi bulk bulk composites, composites, apparent density increases with increasing metallic Bi Bi For LaFe Si apparent density increases with increasing metallic 11.6listed 1.4 1.4 content, as inyTable 1. The theoretical density of LaFe 11.6Si1.4Hy/Bi composites is the sum of the content, as listed in Table 1. The theoretical density of LaFe 11.6Si1.4Hy/Bi composites is the sum of the content, as listeddensity in Table Thecomponent theoretical density of composites is the density sum of the y /Bi 11.6 Si1.4 H theoretical of 1. each multiplied itsLaFe percentages. The values of theoretical theoretical density of each component multiplied its percentages.The The values values of of theoretical density theoretical density of each component multiplied its percentages. theoretical density are much higher than those of the apparent ones. All the samples have similar porosities, which is are are much higher than those of the apparent ones. All the samples have similar porosities, which is much mainly higher caused than those of same the apparent All the samples content have similar porosities, is mainly by the pressure.ones. The small micro-pore of LaFe 11.6Si1.4Hy/Biwhich composites mainly caused by the same pressure. The small micro-pore content of LaFe11.6Si1.4Hy/Bi composites would induce significant The enhancement of thermalcontent conductivity compared with bulk. caused by the samea pressure. small micro-pore of LaFe Si H /Bi composites would y 11.6 1.4 would induce a significant enhancement of thermal conductivity compared with bulk. induce a significant enhancement of thermal conductivity compared with bulk. Table 1. Density, porosity of the LaFe11.6Si1.4Hy/Bi composites with different metallic Bi contents. Table 1. Density, porosity of the LaFe11.6Si1.4Hy/Bi composites with different metallic Bi contents.

Table 1.Metallic Density, Bi porosity of the LaFe with different Bi contents. y /Bi composites Content Theoretical Apparent Densitymetallic Porosity 11.6 Si1.4 HDensity Metallic Bi Content Theoretical Density Apparent Density Porosity (wt %) ρ (g/cm3 3) ρ (g/cm3 3) (%) (wt %) ρ (g/cm ) ρ (g/cm ) (%) Metallic Bi Content Theoretical Density Apparent Density Porosity 5 7.14 6.53 8.52 8.52 (wt %)510 ρ (g/cm37.14 )7.24 ρ (g/cm3 )6.53 (%) 6.61 8.86 10 7.24 6.61 8.86 15 7.35 6.70 8.82 5 7.14 6.53 8.52 15 7.35 6.70 8.82 10 7.24 6.61 8.86 15 7.35 6.70 8.82

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Figure thethe stress-strain curves of the Considering that powder cannotcannot measure Figure3 presents 3 presents stress-strain curves of samples. the samples. Considering that powder compressive strength, we used a bulk mother sample in this work. The maximum compressive strength measure compressive strength, we used a bulk mother sample in this work. The maximum ofcompressive bulk LaFe11.6strength Si1.4 alloy 155 MPa, which is in good agreement withispreviously reported values ofisbulk LaFe11.6 Si1.4 alloy is 155 MPa, which in good agreement with for La(Fe,Si) alloys [27,28]. The maximum values of the compressive strength for Bi powder bonded previously reported values for La(Fe,Si) 13 alloys [27,28]. The maximum values of the compressive 13 samples 5, 10, and 15samples wt % are as high as 263, 306, respectively. strengthcontaining for Bi powder bonded containing 5, 10, and 15 and wt %358 areMPa, as high as 263, 306, Compared and 358 MPa, withcompressive the bulk sample, theofmaximum compressive of the with therespectively. bulk sample,Compared the maximum strength the metallic Bi bonded strength samples increased Bi bonded increased by about 70%,is97%, andhigher 131%, than respectively, which is % much bymetallic about 70%, 97%, samples and 131%, respectively, which much that of the 3 wt epoxy higher than that of the 3 wt % epoxy bonded LaFe 11.7 Si 1.3 C 0.2 H 1.8 (162 MPa) [28], bonded LaFe11.7 Si1.3 C0.2 H1.8 (162 MPa) [28], La0.8 Ce0.2 (Fe0.95 Co0.05 )11.8 Si1.2 /Sn42 Bi58 (303 MPa) [29] La0.8 Ce0.211.6 (FeSi 0.95Co 0.05)11.8Si1.2/Sn42Bi58 (303 MPa) [29] and LaFe11.6Si1.4Hy/Sn (170 MPa) [25]. With the and LaFe 1.4 Hy /Sn (170 MPa) [25]. With the increase of metallic Bi content, more boundaries increaseLaFe of metallic Bi content, more boundaries between LaFe11.6Si1.4Hy particles will be filled, which between 11.6 Si1.4 Hy particles will be filled, which will increase the density and enhance the will increase the density and enhanceThis the binding force of thewettability matrix particles. Thisthe evidences a good binding force of the matrix particles. evidences a good between liquid Bi and the wettability between the liquid Bi and the particles. Furthermore, the toughness of pure metallic is particles. Furthermore, the toughness of pure metallic Bi is better than that of other low meltingBi metals; better than that of other low melting metals; thus, the sample with higher Bi content has a higher thus, the sample with higher Bi content has a higher strain value. strain value.

Figure 3. Compressive stress-strain curves for LaFe11.6Si1.4Hy/Bi composites with 5, 10 and 15 wt % Figure 3. Compressive stress-strain curves for LaFe11.6 Si1.4 Hy /Bi composites with 5, 10 and 15 wt % metallic Bi, respectively, in comparison with that of bulk LaFe11.6Si1.4 compound. metallic Bi, respectively, in comparison with that of bulk LaFe11.6 Si1.4 compound.

Figure 4 shows the M-T curves of LaFe11.6Si1.4H1.4 and the bonded sample LaFe11.6Si1.4Hy/Bi Figure 45,shows M-T curves of theT. bonded LaFe y /Bi 11.6 Si1.4 Hfield 1.4 and 11.6 1.4 His containing 10, andthe 15 wt % metallic Bi LaFe at a magnetic of 0.01 The TC sample of LaFe11.6 Si1.4H 1.4Si alloy containing 5, 10, and 15 K. wtThe % metallic Bi at afrom magnetic The MPa TC ofpressure LaFe11.6 Si alloy determined to be 298 TC decreases 298 tofield 263 of K 0.01 afterT.1625 and 573 1.4 H 1.4 K is vacuum determined to be because 298 K. The TCpartial decreases from 298 to 263 K after MPa pressure and 573 K annealing of the detachment of the H atom. The1625 transition of ferromagnetic vacuum because partial of samples the H atom. The slow, transition of ferromagnetic (FM) toannealing paramagnetic (PM)of forthe LaFe 11.6Si1.4detachment H1.4/Bi bonded becomes illustrating that the magnetic entropy change be adversely by the samples preparation process. The magnetization (FM) to paramagnetic (PM) can for LaFe becomes slow, illustrating that the 11.6 Si1.4 Haffected 1.4 /Bi bonded (M) in the 5 wt % composite higher than others, which due to the lower content The of non-magnetic magnetic entropy change canis be adversely affected by is the preparation process. magnetization phase. In5contrast, M in 10 wt composite lower,which whichismeans cancontent be protected by more (M) in the wt % composite is% higher than is others, due toparticles the lower of non-magnetic binder during the press processing. phase. In contrast, M in 10 wt % composite is lower, which means particles can be protected by more isothermal magnetic entropy change curve of LaFe11.6Si1.4H1.4 and the binderFigure during5a thegives pressthe processing. composites with metallic Bi contents of 5, 10, andentropy 15 wt % under applied fieldHchange of Figure 5a gives the isothermal magnetic changeancurve ofmagnetic LaFe11.6 Si 1.4 1.4 and the 0–2 T. The maximum magnetic entropy change (-ΔS Mmax) for pure LaFe11.6Si1.4H1.4 is 14.6 J/kg K. In composites with metallic Bi contents of 5, 10, and 15 wt % under an applied magnetic field change parallel, the -ΔSMmax are 7.8, 7.4, and 6.1 J/kg K for the composites with metallic Bi contents of 5, 10, of 0–2 T. The maximum magnetic entropy change (-∆SM max ) for pure LaFe11.6 Si1.4 H1.4 is 14.6 J/kg K. and 15 wt %, respectively. Obviously, the -ΔSMmax of the composited samples shows a decreased In parallel, the -∆SM max are 7.8, 7.4, and 6.1 J/kg K for the composites with metallic Bi contents of 5, tendency with increasing metallic Bi content, which may originate from the decrease of the NaZn13 10, and 15 wt %, respectively. Obviously, the -∆SM max of the composited samples shows a decreased phase and the cracks induced by the pressing of 1625 MPa, as observed in the SEM image. As tendency with increasing metallic Bi content, which may originate from the decrease of the NaZn13 reported in ref. [30], the smaller MCE was due to the removal of extrinsic hysteresis and the phase and the cracks induced by the pressing of 16251:13 MPa,particles. as observed in the image. As reported diminishing of grain boundaries of the small Figure 5bSEM shows temperature independence ref. [30], the of smaller MCE was to the removal of extrinsic hysteresis and the diminishing of grain volumetric -ΔSdue M for pure LaFe11.6Si1.4H1.4 and LaFe11.6Si1.4Hy/Bi composites with boundaries of the small 1:13 particles. 5b shows temperature of volumetric -∆SM different metallic Bi contents under aFigure magnetic field change of 0–2dependence T. Considering the practical forapplication, pure LaFe11.6 Si H and LaFe Si H /Bi composites with different metallic Bi contents under 1.4 1.4 1.4 yexpression of the isothermal magnetic entropy change, it is necessary to give11.6 another

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a Materials magnetic field change of 0–2 T. Considering the practical application, it is necessary to give5another 2018, 11, x FOR PEER REVIEW of 7 Materials 2018, 11, xisothermal FOR PEER REVIEW 5 of 7 expression of the magnetic entropy change, i.e., volumetric magnetic entropy change. It can bei.e., seen that themagnetic maximum values of theItvolumetric aremaximum as high as 51, 49, andvolumetric 35 mJ/cm3 K volumetric entropy change. can be seen-∆S thatMthe values of the i.e., volumetric magnetic entropy change. It can be seen that the maximum values of the volumetric 3K10, around 263 for as the51,composites with 5, and 15 contents, respectively. these -ΔSM are as K high 49, and 35 mJ/cm around 263wt K% forBi the composites with 5, 10, Although and 15 wt % -ΔSM are as high as 51, 49, and 353 mJ/cm3K around 263 K for the composites with 5, 10, and 15 wt % 3K for pure LaFe11.6Si1.4H1.4, Bi contents, respectively. values are11.6 lower mJ/cm values are lower than 102Although mJ/cm Kthese for pure LaFe Si1.4than H1.4102 , such maxima are close to those of the Bi contents, respectively. Although these values are lower than 102 mJ/cm33K for pure LaFe11.6 Si1.4H1.4, 3 3 such11.7maxima are to thoseK)ofcomposites the LaFe11.7[28] Si1.3and C0.2HLa(Fe,Mn,Si) 1.8 (54.7 mJ/cm composites and LaFe Si1.3 C0.2 H (54.7 mJ/cm mJ/cm[28] K) bonded y3 (55–65 1.8 close 13 HK) such maxima are close to those of the LaFe11.7Si1.3C0.2H1.8 (54.7 mJ/cm K) composites [28] and 13Hy (55–65 bonded by the epoxy resin [31]. byLa(Fe,Mn,Si) the epoxy resin [31]. mJ/cm3K) La(Fe,Mn,Si)13Hy (55–65 mJ/cm3K) bonded by the epoxy resin [31].

Figure4.4.Temperature Temperaturedependence dependence of of magnetization magnetization measured 1.4HyH /Bi Figure measured under under0.01 0.01TT for for LaFe LaFe11.6SiSi 1.4 y /Bi Figure 4. Temperature dependence of magnetization measured under 0.01 T for LaFe11.6 11.6Si1.4Hy/Bi 11.6Si1.4 compound. composites with different low-melting alloy contents and LaFe composites with different LaFe11.6 compound. 11.6 SiSi 1.41.4 compound. composites with differentlow-melting low-meltingalloy alloycontents contents and and LaFe

Figure 5. (a) Temperature dependence of mass ΔSM for LaFe11.6Si1.4H1.4 and LaFe11.6Si1.4Hy/Bi Figure 5. (a) Temperature dependence of mass ΔSM for LaFe11.6Si1.4H1.4 and LaFe11.6Si1.4Hy/Bi Figure 5. (a)with Temperature dependence of mass for LaFe Si1.4 H1.4 LaFe composites different metallic Bi contents under∆S aM magnetic field of and 2 T; (b) Temperature 11.6change 11.6 Si1.4 Hy /Bi composites with different metallic Bi contents under a magnetic field change of 2 T; (b) Temperature composites with metallic contents a magnetic field change of 2 T;with (b) Temperature 11.6Si1.4under H1.4 and LaFe11.6Si1.4 Hy/Bi composites different dependences of different volumetric ΔSM forBiLaFe dependences of volumetric ΔSM for LaFe11.6Si1.4H1.4 and LaFe11.6Si1.4Hy/Bi composites with different metallic Bi contents under a∆S magnetic field change of 2and T. LaFe11.6 Si1.4 Hy /Bi composites with different dependences of volumetric Si1.4 H1.4 M for LaFe 11.6 metallic Bi contents under a magnetic field change of 2 T. metallic Bi contents under a magnetic field change of 2 T.

4. Conclusions 4. Conclusions 4. Conclusions We have fabricated the LaFe11.6Si1.4Hy/Bi magnetocaloric composites with two-phase alternating We have fabricated the LaFe11.6Si1.4Hy/Bi magnetocaloric composites with two-phase alternating distribution by vacuum annealing after cold pressing. The with crystal structurealternating of the We have microstructure fabricated the LaFe Si1.4 H composites two-phase y /Bi magnetocaloric distribution microstructure by 11.6 vacuum annealing after cold pressing. The crystal structure of the matrix LaFe11.6Si1.4H1.4 shows no disruption, and the mechanical property of the composite was distribution microstructure by vacuum annealing after pressing.property The crystal of the matrix matrix LaFe 11.6Si1.4H1.4 shows no disruption, and thecold mechanical of structure the composite was improved by the continuous increase of the metallic Bi among the matrix particles. The maximum LaFe Si H shows no disruption, and the mechanical property of the composite was improved improved 11.6 1.4 by 1.4the continuous increase of the metallic Bi among the matrix particles. The maximum values of the compressive strength for LaFe11.6Si1.4Hy/Bi composites with Bi contents of 5, 10, and 15 byvalues the continuous increase of the metallic Bi among particles. The maximum of the compressive strength for LaFe 11.6Si1.4Hthe y/Bi matrix composites with Bi contents of 5, values 10, andof15the wt % are as high as 263, 306, and 358 MPa, and the corresponding volumetric -ΔSMmax are 51, 49, and wt % are3 asstrength high as 263, 306, and 358 MPa, the corresponding volumetric are compressive for LaFe Si H composites with Bi contents of 5,-ΔS 10,Mmax and 1551, wt49, % and are as y /Biand 11.6 1.4 35 mJ/cm K under ΔH of 0–2 T at 263 K, respectively. The Curie temperature decreases to 263 K after 3 max are 3K under ΔH of 0–2 T at 263 K, respectively. The Curie temperature 35 as mJ/cm decreases to 263 K after high 263, 306, and 358 MPa, and the corresponding volumetric -∆S 51, 49, and 35 mJ/cm M useful way to prepare the K pressure and vacuum annealing. The current study may provide a rising pressure and vacuum annealing. The current study may provide a rising useful way to prepare the La-Fe-Si based-magnetocaloric composites. La-Fe-Si based-magnetocaloric composites.

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under ∆H of 0–2 T at 263 K, respectively. The Curie temperature decreases to 263 K after pressure and vacuum annealing. The current study may provide a rising useful way to prepare the La-Fe-Si based-magnetocaloric composites. Author Contributions: L.L. and Z.L. conceived and designed the experiments; Z.L., Q.W., N.S. and Z.D. performed the experiments; Z.L. and L.L. analyzed the data; Z.L. and L.L. wrote the paper. Acknowledgments: This work was supported by the National Natural Science Foundation of China (Grant No. 51671048), the Fundamental Research Funds for the Central Universities (Grant Nos. N170904001 and N170908001), and Research Funds for Innovation Talents in Universities and Colleges of Liaoning Province (Grant No. LR2016003). Conflicts of Interest: The authors declare no conflict of interest.

References 1. 2. 3. 4. 5. 6.

7. 8.

9. 10. 11. 12. 13. 14. 15. 16.

17.

Yu, B.F.; Gao, Q.; Zhang, B.; Meng, X.Z.; Chen, Z. Review on research of room temperature magnetic refrigeration. Int. J. Refrig. 2003, 26, 622–636. [CrossRef] Zhang, Y.; Li, H.D.; Wang, J.; Li, X.; Ren, Z.; Wilde, G. Structure and cryogenic magnetic properties in Ho2 BaCuO5 cuprate. Ceram. Int. 2018, 44, 1991–1994. [CrossRef] Li, L.W. Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals. Chin. Phys. B 2016, 25, 037502. [CrossRef] Zhang, Y.K.; Guo, D.; Li, H.; Geng, S.; Wang, J.; Li, X.; Ren, Z.M.; Wilde, G. Low field induced large magnetic entropy change in the amorphousized Tm60 Co20 Ni20 ribbon. J. Alloys Compd. 2018, 733, 40–44. [CrossRef] Li, L.; Su, K.; Huo, D. Large reversible normal and inverse magneto-caloric effects in the RE2 BaCuO5 (RE = Dy and Er) compounds. J. Alloys Compd. 2018, 735, 773–776. [CrossRef] Zhang, Y.K.; Yang, Y.; Hou, C.J.; Guo, D.; Wang, J.; Geng, S.H.; Li, X.; Ren, Z.M.; Wilde, G. Metamagnetic transition and magnetocaloric properties in antiferromagnetic Ho2 Ni2 Ga and Tm2 Ni2 Ga compounds. Intermetallics 2018, 94, 17–21. [CrossRef] Li, L.W.; Yuan, Y.; Qi, Y.; Wang, Q.; Zhou, S. Achievement of a table-like magnetocaloric effect in the dual-phase ErZn2 /ErZn composite. Mater. Res. Lett. 2018, 6, 67–71. [CrossRef] Yang, Y.; Zhang, Y.; Xu, X.; Geng, S.; Hou, L.; Li, X.; Ren, Z.; Wilde, G. Magnetic and magnetocaloric properties of the ternary cadmium based intermetallic compounds of Gd2 Cu2 Cd and Er2 Cu2 Cd. J. Alloys Compd. 2017, 692, 665–669. [CrossRef] Wang, G.F.; Mu, L.J.; Zhang, X.F.; Zhao, Z.R.; Huang, J.H. Hydriding and dehydriding kinetics in magnetocaloric La(Fe,Si)13 compounds. J. Appl. Phys. 2014, 115, 143903. [CrossRef] Lyubina, J.; Schäfer, R.; Martin, N.; Schultz, L.; Gutfleisch, O. Novel Design of La(Fe,Si)13 Alloys Towards High Magnetic Refrigeration Performance. Adv. Mater. 2010, 22, 3735–3739. [CrossRef] [PubMed] Smith, A.; Bahl, C.R.H.; Bjørk, R.; Engelbrecht, K.; Nielsen, K.K.; Pryds, N. Materials Challenges for High Performance Magnetocaloric Refrigeration Devices. Adv. Energy Mater. 2012, 2, 1288–1318. [CrossRef] Yu, B.F.; Liu, M.; Egolf, P.W.; Kitanovski, A. A review of magnetic refrigerator and heat pump prototypes built before the year 2010. Int. J. Refrig. 2010, 33, 1029–1060. [CrossRef] Wada, H.; Tanabe, Y. Giant magnetocaloric effect of MnAs1 −x Sbx . Appl. Phys. Lett. 2001, 79, 3302–3304. [CrossRef] Hu, F.X.; Shen, B.G.; Sun, J.R. Magnetic entropy change in Ni51.5 Mn22.7 Ga25.8 alloy. Appl. Phys. Lett. 2000, 76, 3460–3462. [CrossRef] Krenke, T.; Duman, E.; Acet, M.; Wassermann, E.F.; Moya, X.; Mañosa, L.; Planes, A. Inverse magnetocaloric effect in ferromagnetic Ni–Mn–Sn alloys. Nat. Mater. 2005, 4, 450–454. [CrossRef] [PubMed] Lei, T.; Nielsen, K.K.; Engelbrecht, K.; Bahl, C.R.H.; Bez, H.N.; Veje, C.T. Sensitivity study of multi-layer active magnetic regenerators using first order magnetocaloric material La(Fe,Mn,Si)13 Hy . J. Appl. Phys. 2015, 118, 014903. [CrossRef] Fujita, A.; Fujieda, S.; Hasegawa, Y.; Fukamichi, K. Itinerant-electron metamagnetic transition and large magnetocaloric effects in La (Fex Si1 −x )13 compounds and their hydrides. Phys. Rev. B 2003, 67, 104416. [CrossRef]

Materials 2018, 11, 943

18.

19.

20.

21.

22.

23.

24.

25. 26. 27.

28.

29.

30. 31.

7 of 7

Skokov, K.P.; Karpenkov, D.Y.; Kuzmin, M.D.; Radulov, I.A.; Gottschall, T.; Kaeswurm, B.; Fries, M.; Gutfleisch, O. Heat exchangers made of polymer-bonded La(Fe,Si)13 . J. Appl. Phys. 2014, 115, 17A941. [CrossRef] Zhang, H.; Sun, Y.J.; Li, Y.W.; Wu, Y.Y.; Long, Y.; Shen, J.; Hu, F.X.; Sun, J.R.; Shen, B.G. Mechanical properties and magnetocaloric effects in La(Fe, Si)13 hydrides bonded with different epoxy resins. J. Appl. Phys. 2015, 117, 063902. [CrossRef] Pulko, B.; Tušek, J.; Moore, J.D.; Weise, B.; Skokov, K.; Mityashkin, O.; Kitanovski, A.; Favero, C.; Fajfar, P.; Gutfleisch, O.; et al. Epoxy-bonded La–Fe–Co–Si magnetocaloric plates. J. Magn. Magn. Mater. 2015, 375, 65–73. [CrossRef] Imamura, W.; Coelho, A.A.; Kupfer, V.L.; Carvalho, A.M.G.; Zago, J.G.; Rinaldi, A.W.; Favaro, S.L.; Alves, C.S. A new type of magnetocaloric composite based on conductive polymer and magnetocaloric compound. J. Magn. Magn. Mater. 2017, 425, 65–71. [CrossRef] You, C.; Wang, S.; Zhang, J.; Yang, N.; Tian, N. Improvement of magnetic hysteresis loss, corrosion resistance and compressive strength through spark plasma sintering magnetocaloric LaFe11.65 Si1.35 /Cu core-shell powders. AIP Adv. 2016, 6, 055321. [CrossRef] Radulov, I.A.; Karpenkov, D.Y.; Skokov, K.P.; Karpenkov, A.Y.; Braun, T.; Brabander, V.; Gottschall, T.; Pabst, M.; Stoll, B.; Gutfleisch, O. Production and properties of metal-bonded La(Fe,Mn,Si)13 Hx composite material. Acta Mater. 2017, 127, 389–399. [CrossRef] Krautz, M.; Funk, A.; Skokov, K.P.; Gottschall, T.; Eckert, J.; Gutfleisch, O.; Waske, A. A new type of La (Fe,Si)13 -based magnetocaloric composite with amorphous metallic matrix. Scr. Mater. 2015, 95, 50–53. [CrossRef] Zhang, H.; Liu, J.; Zhang, M.; Shao, Y.; Li, Y.; Yan, A. LaFe11.6 Si1.4 Hy /Sn magnetocaloric composites by hot pressing. Scr. Mater. 2016, 120, 58–61. [CrossRef] Raynor, G.V.; Smith, R.W. The transition temperature of the transition between grey and white tin. Proc. R. Soc. Lond. A 1958, 244, 101–109. [CrossRef] Zhang, M.X.; Liu, J.; Zhang, Y.; Dong, J.D.; Yan, A.; Skokov, K.P.; Gutfleisch, O. Large entropy change, adiabatic temperature change, and small hysteresis in La(Fe,Mn)11.6 Si1.4 strip-cast flakes. J. Magn. Magn. Mater. 2015, 377, 90–94. [CrossRef] Zhang, H.; Sun, Y.J.; Niu, E.; Hu, F.X.; Sun, J.R.; Shen, B.G. Enhanced mechanical properties and large magnetocaloric effects in bonded La(Fe, Si)13 -based magnetic refrigeration materials. Appl. Phys. Lett. 2014, 104, 062407. [CrossRef] Dong, X.T.; Zhong, X.C.; Peng, D.R.; Huang, J.H.; Zhang, H.; Jiao, D.L.; Liu, Z.W.; Ramanujan, R.V. La0.8 Ce0.2 (Fe0.95 Co0.05 )11.8 Si1.2 /Sn42 Bi58 magnetocaloric composites prepared by low temperature hot pressing. J. Alloys Compd. 2018, 737, 568–574. [CrossRef] Hu, F.X.; Chen, L.; Wang, J.; Bao, L.F.; Sun, J.R.; Shen, B.G. Particle size dependent hysteresis loss in La0.7 Ce0.3 Fe11.6 Si1.4 C0.2 first-order systems. Appl. Phys. Lett. 2012, 100, 072403. [CrossRef] Radulov, I.A.; Skokov, K.P.; Karpenkov, D.Y.; Gottschall, T.; Gutfleisch, O. On the preparation of La (Fe,Mn,Si)13 Hx polymer-composites with optimized magnetocaloric properties. J. Magn. Magn. Mater. 2015, 396, 228–236. [CrossRef] © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).