Er2-xPrxFe17磁致冷合金在室温区的磁熵变

在氩保护气氛中用熔炼法制备了Er2-xPrxFe17系列合金，通过X射线衍射和SQUID磁强计研究了样品的结构和磁熵变。结果表明，Er2-xPrxFe17系列合金具有六方Th2Ni17型结构，通过成分微调使其居里温度处在室温附近，Er2-xPrxFe17合金有较大的磁熵变，且致冷温区较宽，是一类有很大应用潜力的室温磁致冷材料。     

Magnetocaloric effect of （Gd1-xNdx）Co2 alloys in low magnetic field

The phases and magnetocaloric effect in the alloys （Gd1-xNdx）Co2 with x = 0, 0.1, 0.2, 0.3, and 0.4 were investigated by X-ray diffraction analysis and magnetization measurement. The samples are single phase with a cubic MgCu2-type structure. The To decreases obviously with increasing Nd content from 404 K of the alloy with x = 0 to 272 K of the alloy with x = 0.4; forx = 0.3, the To is 296 K, which is near room temperature. In the samples （Gd1-xNdx）Co2 with x = 0.0, 0.1, 0.2, 0.3, and 0.4, the maximum magnetic entropy change is 1.471, 1.228, 1.280, 1.381 and 1.610 J·kg^-1·K^-1, respectively, in the applied field range of 0-2.0 T. The results of Arrott plots confirmed that the transition type were second order magnetic transition forx = 0, 0.3, and 0.4.     

基于第一性原理计算V元素对高熵合金Al0.4Co0.5VxFeNi的组织及性能影响

采用第一性密度泛函理论,结合虚拟晶体近似（VCA）的方法建立晶体结构模型,开展高熵合金Al0.4Co0.5Vx FeNi的结构性能、弹性性能及基态能量计算。根据能量最低原理可确定,Al0.4Co0.5Vx FeNi高熵合金的最优K-point值为12×12×12,截断能为1000 eV。计算结果表明：Al0.4Co0.5Vx FeNi系高熵合金均可生成fcc+bcc结构,fcc的力学稳定性明显优于bcc的力学稳定性。V元素含量由0.2增至0.8时,bcc点阵常数降低约4%,fcc晶格常数降低约6%。随着V元素的增加,Al0.4Co0.5Vx FeNi合金的体模量、剪切模量逐渐减小。V元素含量为0.8时,bcc结构的泊松比异常增加,进一步说明了随着V元素含量的增加,材料的塑性变形能力降低,材料的脆性增加。经试验验证,Al0.4Co0.5Vx FeNi系高熵合金均由fcc和bcc组成,组织形貌均为两相组织;V元素含量由0.2升至0.8时,延伸率降低约85%,该试验结果与第一性原理计算的结果较为吻合。     

室温磁致冷合金Pr2Fe17-xCox的结构、磁性和磁熵变

在氩气气氛中用熔炼法制备了Pr2Fe17-xCox系列合金，通过粉末X射线衍射和SQUID磁强计研究了样品的结构、磁性和磁熵变。结果表明：Pr2Fe17-xCox系列合金具有菱方Th2Zn17型结构；通过成分微调使其居里温度处在室温附近：Pr2Fe17-xCox，系列合金有较大的磁熵变，在低场下的磁熵变是金属Gd的65％～73％，而高场下的磁熵变则为金属Gd的63％～68％；但其成本约为金属Gd的1／10，具有很高的性价比，是一类有很大应用潜力的室温磁致冷材料。     

Co掺杂对Ni-Mn-Sn铁磁形状记忆合金磁性质的影响(英文)

采用第一性原理计算揭示了Co掺杂对Ni-Mn-Sn形状记忆合金磁性质的影响。结果表明,掺杂Co使Ni-Mn-Sn合金中两相饱和磁化强度差增大的原因在于其奥氏体的Mn-Mn磁交换作用由反铁磁性转变为铁磁性。奥氏体的顺磁态与铁磁态的能量差对Ni-Co-Mn-Sn的磁转变有重要影响。此外,Co掺杂对磁性的影响与Mn 3d态的改变有关。     

Ce 含量对 Mg2.2Sn1Al0.5Zn合金显微组织和力学性能的影响

利用 OM、XRD、SEM、EDS 等方法,研究了不同Ce 含量对 Mg-2.2Sn-1Al-0.5Zn 合金显微组织和力学性能的影响。结果表明：添加适量的稀土 Ce 能细化晶粒,Ce 与 Al 结合形成高熔点的稀土相 Al4Ce,使β-Mg17Al12相数量减少;针状或杆状 Al4Ce 相分布在晶界周围,阻止了位错运动;合金的抗拉强度、塑性和硬度均随 Ce 含量的增加呈现先增加后降低的趋势,当 Ce 含量为0.6%时合金的力学性能最佳。对断口进行扫描分析证明拉伸断裂为穿晶断裂和韧性断裂的混合断裂。     

Mn含量对Mn基Heusler合金磁及磁热性能影响

选用Mn基Heusler合金为研究对象。通过电弧熔炼和热处理制备样品,并用甩带法制成薄带形状。采用X射线衍射仪和振动样品磁强计等分析仪器测试了样品的晶体结构、磁及磁热性能,分析了Mn含量对材料晶体结构、磁和磁热性能的影响。研究发现,Mn2-xSn0.5Ga0.5合金在常温下为六方结构,在室温附近仅发生一次二阶磁性转变,无明显磁滞和热滞。居里温度和饱和磁化强度对Mn含量非常敏感,随着Mn含量升高,居里温度和饱和磁化强度均出现下降,由Mn1.2Sn0.5Ga0.5的304 K和64.1 emu/g分别降至Mn2Sn0.5Ga0.5的262 K和46.7 emu/g,这表明合金中的磁矩呈亚铁磁形态分布。由于没有磁滞和热滞,室温附近较大的工作温度区间,因此,该材料在磁制冷领域具有很好的应用前景。     

Prediction of structure and elastic properties of AlCrFeNiTi system high entropy alloys

The effect of alloy compositions on structure and elastic properties of single-phase AlCrFeNiTi and AlCrFeNiTiX (X = V, Mn, Co, Zn, Zr, Nb, Mo and La) high entropy alloys was investigated by calculating solid solution characteristics of alloys combining with the first principles method. The obtained formation enthalpy, cohesive energy and mechanical stability indicated AlCrFeNiTi and AlCrFeNiTiX (X = V, Mn, Co, Nb and Mo) HEAs adopt the body centered cubic structure instead of face centered cubic structure. There is a rather good agreement between theoretical structure predictions and the classic criteria of valence electron concentration VEC. A detailed investigation on electronic structure of AlCrFeNiTi and AlCrFeNiTiX alloys revealed the bonding behavior of alloys. In addition, the calculated results of polycrystalline elastic parameters confirmed the ductility of AlCrFeNiTiX alloys would weaken with increasing mixing enthalpy ΔH_mix (or decreasing atomic size difference δ), and the increase in ΔH_mix is predicted to decrease the elastic anisotropy. Furthermore, we predicted that the present high entropy alloys should be more elastically isotropic when the corresponding the mixing enthalpy ΔH_mix has a larger value.     

Microstructure and mechanical properties of Mg-8Li-2Zn-0.5(Ce, Y) alloys

0.5 wt.% Ce and Y were added into the alloy of Mg-8Li-2Zn, respectively. The different behaviors of Ce and Y in the alloy were investigated. Results show that, Ce and Y can both refine the α phase, and the α phase was spheroidized. Two kinds of compounds exist in the alloy when the alloy contains Ce/Y. They are Zn₂Ce and Mg₆Y, respectively. Zn₂Ce mainly distributes at the grain boundary of the alloy with the shape of blocky. Mg₆Y mainly distributes in the inner place of grains with the shape of granular. The size of Zn₂Ce is much larger than that of Mg₆Y. Y and Ce are both favorable for the improvement of strength, and the effect of Y is more obvious. The addition of Ce makes the elongation of the alloy become poor, while the addition of Y can increase the elongation of the alloy.     

GdDyFe、GdTbFe合金的磁熵研究

研究了Gd0.5Td0.5-xFex,Gd0.5Dy0.5-yFey(x=0.1,0.2,0.3,0.4；y=0.1,0.2,0.3,0.4)系列稀土合金在245～320K温区范围的磁熵变，发现这二种系列合金均具有较大的磁熵变值，适合作为中等磁场（1～2T）下的室温磁制冷材料。     

Influence of Cu content on high temperature oxidation behavior of AlCoCrCuxFeNi high entropy alloys (x = 0; 0.5; 1)

Studies on the oxidation behavior of high entropy alloys from the Al-Co-Cr-Cu-Fe-Ni metallic system were conducted. Three different high entropy alloys were synthesized using arc-melting method: AlCoCrFeNi, AlCoCrCu_0.5FeNi and AlCoCrCuFeNi, with their crystal structures being respectively BCC, BCC and BCC + FCC. All alloys were oxidized in the air atmosphere at temperature of 1273 K for different time periods. Basing on the thermogravimetric result, the oxidation rate of the materials decreased with the increase of Cu content and the values of parabolic constants were on the level similar to those observed in Ni-Al intermetallic alloys. In all cases the oxide scale consisted of α-Al₂O₃, which exhibited poor adhesion to the surface during the cooling process, what was especially visible in alloys with Cu addition. In all oxidized samples a tendency towards formation of the Al-depleted FCC phase directly beneath the scale was observed. The phase constitution of all materials changed significantly during the oxidation process, with multiple new phases appearing in the system.     

Effect of Co element on microstructure and mechanical properties of FeCoXNiCuAl alloys

FeCox NiCuAl (x values in molar ratio, x=0.2, 0.5, 1, 1.5, 2 and 3) alloys were prepared using a suck-casting method. The effect of Co element on phase constituents, microstructure and mechanical properties of the FeCox NiCuAl alloys was investigated using X-ray diffraction, scanning electron microscopy, optical microscopy and compressive tests. It was found that the Co addition has a significant influence on the structure and properties of the FeCox NiCuAl alloys. The alloys have typical dendrite microstructure, and are composed of a simple fcc structure and bcc structure. The addition of Co promotes the formation of fcc phase in the alloys, retards the compressive strength and hardness of the alloys, and enhances the plasticity of the alloys.     

Composition dependence of structure,physical and mechanical properties of FeCoNi(MnAl)x high entropy alloys

This paper has provided a systematic study of the crystal structure, physical and mechanical properties of FeCoNi(MnAl)_x (0 ≤ x ≤ 2) high entropy alloys. As x increases, the crystal structure changes from FCC to FCC + BCC then to BCC solid solution. High saturated magnetization, low coercivity together with high electric resistivity are found in this system, indicating their potential applications as soft magnets. Meanwhile, the strength and hardness increase monotonously as x increases. Optimal balance of physical and mechanical properties are obtained in this system.     

退火对AlCuFeNiTiCrx高熵合金硬度的影响

采用铜模吸铸法制备AlCuFeNiTiCr_x(x=0.5, 1.0, 1.5, 2.0)高熵合金,并在1000℃下进行3 h退火处理。通过X射线衍射仪(XRD)、光学显微镜、维氏硬度计,分别测试了铸态和退火态AlCuFeNiTiCr_x(x=0.5, 1.0, 1.5, 2.0)高熵合金的微观结构演变及维氏硬度值。发现铸态和退火态试样仅由简单的体心立方(BCC)和面心立方(FCC)固溶体相组成,而退火态试样中的FCC相与铸态试样中的FCC相相比有所增加。根据金相显微照片,两种状态下的高熵合金仅存在枝晶和晶间相,且退火后的显微组织变得更加均匀。两种状态下高熵合金的硬度均随Cr含量的增加而增加,且退火态试样的硬度值远大于铸态试样。     

Co含量对FeCoPB非晶合金软磁性能和弯曲韧性的影响

采用熔体旋淬的方法制备了Fe Co含量达到87 at%Fe-Co-P-B系非晶合金薄带,研究了金属元素Co对Fe-Co-P-B系非晶合金的形成能力、软磁性能和弯曲韧性的影响规律。该合金系具有高的饱和磁化强度1.75～1.84 T,且热处理后薄带仍具有良好的弯曲韧性。添加Co元素后,提高了合金的居里温度,矫顽力升高。对薄带样品施加12 MPa的拉应力,合金的矫顽力由12.8 A/m降低到6.5 A/m。因此,通过成分和应力的调控可以避免Fe基非晶合金热处理引起的弛豫脆性问题,为获得具有优异软磁性能和良好弯曲韧性的Fe基非晶合金提供重要途径。     

Influence of Sn substitution for Co in RCo2 （R = Gd, Tb, Dy） alloys on the structure and magnetocaloric effect

The phases and the magnetocaloric effect in the alloys R(Co1-xSnx)2 with x=0, 0.025, 0.050, 0.075, and 0.100 were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in RCo2 is limited. The cubic MgCu2-type structure for the alloys of RCo2 was confirmed by X-ray powder diffraction and the remaining alloys mainly consisted of the RCo2 phase, along with some RCo3 and R5Sn3 impurity phases. The impurity phases increase with the increase of Sn content. The Tc of the alloys is not very sensitive to the Sn substitution for Dy(Co1-xSnx)2 and Tb(Co1-xSnx)2, whereas in Gd(Co1-xSnx)2, the Curie temperatures significantly increase. The maximum magnetic entropy changes in the alloys Dy(Co1-xSnx)2 (x=0,0.025, 0.050, 0.075) are 5.78, 5.43, 3.88, and 2.98 J·kg-1·K-1, respectively, and those in the Tb(Co1-xSnx)2 (x =0,0.025) are 3.44, and 2.29 J·kg-1·K-1 respectively in the applied field change of 0-2.0 T.     

Near room temperature magnetic entropy changes in as-cast Gd100−xMnx (x = 0, 5, 10, 15, and 20 at.%) alloys

A series of Gd_100−xMn_x (x = 0, 5, 10, 15, and 20 at.%) alloys were prepared by arc-melting. The Curie temperature (T_C) associated with the ferromagnetic-paramagnetic transitions, derived from M-T curves, show decrease in T_C for as-cast alloys (∼279 K) as compared to as-cast Gd (∼292 K). No appreciable decrease in the |ΔS_M|_max values ∼4.6 J/kg K (0-2 T) and ∼8.6 J/kg K (0-5 T) were observed upon alloying Gd with Mn up to x ≤ 15 at.%. Refrigerant capacity (q) showed negligible variation ∼195 J/kg (0-2 T) and ∼450 J/kg (0-5 T) with increasing Mn (up to x ≤ 15 at.%) content. Similar values of |ΔS_M|_max and q coupled with ∼13 K decrease in T_C for as-cast Gd_100−xMn_x (0 ≤ x ≤ 15) alloys as compared to Gd, suggests expansion of working temperature region of Gd upon alloying with Mn up to 15 at.%. Low cost, adjustable T_C, favorable magnetocaloric properties make Gd_100−xMn_x alloys potential candidates as second-order transition based magnetic refrigerants for near room temperature air-conditioning and magnetic refrigeration.     

Ni45．4＋xMn41．5-xSn13．1（x=0，1．5，3．0）合金的结构和磁熵变研究

铁磁形状记忆合金Ni45.4-xMn41.5-xSn13.1（x=0,1．5,3．0）（分别定义为样品1、2、3）系列通过电弧熔炼法制备得到。在1173K下真空退火24h,自然冷却至室温。利用X射线衍射仪和振动样品磁强计研究了合金的结构、磁性和磁熵变。等温磁化曲线和Arrott曲线表明合金在马氏体转变温度附近合金为典型的亚磁性状态。在1．2T的外场下样品2和3在马氏体转变温度附近发生大的磁熵变大小分别为3．8和3．7J／kgK。样品1在磁性转变温度附近的磁熵变大小为2．24J／kg·K。     

Gd1-xVx系列合金的磁热效应研究

采用真空电弧熔炼方法制备Gd1-xVx(x=0.01,0.03,0.05,0.07,0.09)系列合金.研究发现:Gd1-xVx合金完全保持了纯Gd的六方型晶体结构,其在居里温度附近的磁特性符合二级相变规律;合金居里温度比纯Gd低1～2 K,并且随x的增加变化很小;在低磁场下Gd1-xVx合金具有较大的磁熵变、绝热温变以及较宽的ΔSM-T 曲线峰,并且所有样品的相对制冷能力都明显优于纯Gd.