Twin structure in Mn−Ni−Ti intermetallic alloys with a thermoelastic martensitic transformation

The formation of a twin structure in an alloy can occur in plastic deformation, in subsequent annealing, and as a result of a martensitic transformation. Martensitic transformations that occur in cooling of alloys whose structure includes Hume-Rothery phases are often of a thermoelastic nature and finish with formation of martensite of a twin type. It is of interest to determine the parameter of the twin structure, in particular, the mean width of the first-order twins, and establish its relationship with the properties of the martensite phase in Mn−Ni−Ti alloys. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 17–20, April, 1998.     

Magnetocaloric effect of Pr2Fe17−x Mn x alloys

Polycrystalline Pr2Fe17-xMnx（x = 0, 1, and 2）alloys were studied by X-ray diffraction（XRD）, heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic–ferromagnetic transition. For an applied field change from0 to 5 T, the maximum-△SM for Pr2Fe17-xMnxalloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 J·kg^-1·K^-1,respectively. The refrigerant capacity（RC） values range from 458 to 364 J·kg^-1, which is about 70 %–89 % that of Gd. The large, near room temperature △SM and RC values,chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnxalloys be selectable materials for room temperature magnetic refrigeration applications.     

Structural state of metastable cubic compounds Ni1 − x Zn x O (0.6 ≤ x ≤ 0.99)

The fine crystalline structure of metastable cubic oxide compounds Ni_{1 ? x} Zn _x O (0.6 ≤ x ≤ 0.99) has been examined using X-ray diffraction. The compounds have been synthesized from the original hexagonal phase by quenching specimens from an elevated temperature under an external hydrostatic pressure. It has been found that the diffraction patterns of the compounds include a system of superlattice diffuse maxima, the number and intensity of which depend greatly on their composition. The origin of this superstructure is discussed.     

THERMODYNAMIC STABILITY OF COMPLEX OXIDE Sm_(1+x)Ba_(2-x)Cu_3O_y(0≤x≤0.4)

用测量固体电解质电池电动势的方法，测试了Ｓｍ－Ｂａ－Ｃｕ－Ｏ体系主要化合物的标准Ｇｉｂｂｓ生成自由能；结果发现稀土复合氧化物Ｓｍ１＋ｘＢａ２－ｘＣｕ３Ｏｙ随着固溶度ｘ增加。化合物稳定性下降。ＤＴＡ实验支持这一结论。     

Stress-induced martensitic transformation in （Ni47Ti44）100-xNbx shape memory alloys with wide hysteresis

The effect of deformation via stress-induced martensitic transformation on the reverse transformation behavior of the （Ni47Ti44）100-xNbx （x=3, 9, 15, 20, 30, mole fraction, %） shape memory alloys was investigated in detail by differential scanning calorimetry （DSC） after performing cryogenic tensile tests at a temperature of Ms＋30 ℃. The results show that Nb-content has obvious effect on the process of stress-induced martensitic transformation. It is also observed that the stress-induced martensite is stabilized relative to the thermally-induced martensite （TIM） formed on cooling, and Nb-content in Ni-Ti-Nb alloy has great influence on the reverse transformation start temperature and transformation temperature hysteresis of stress-induced martensite（SIM）. The mechanism of wide transformation temperature hysteresis was fully explained based on the microscopic structure and the distribution of the elastic strain energy of （Ni47Ti44）100-xNbx alloys.     

Composition-dependent crystal structure and martensitic transformation in Heusler Ni–Mn–Sn alloys

In the present work, modulated four- and five-layered orthorhombic, seven-layered monoclinic (4O, 10M and 14M) and unmodulated double tetragonal (L1₀) martensites are characterized in Heusler Ni–Mn–Sn alloys using X-ray diffraction, high-resolution transmission electron microscopy, electron diffraction techniques and thermal analysis. All modulated layered martensites exhibit twins and stacking faults, while the L1₀ martensite shows fewer structural defects. The substitution of Sn with Mn in Ni₅₀Mn_37+xSn_13?x (x = 0, 2, 4) enhances the martensitic transition temperatures, while the transition temperatures decrease with increasing Mn content for constant Sn levels in Ni_50?yMn_37+ySn₁₃ (y = 0, 2, 4). The compositional dependence of the martensitic transition temperatures is mainly attributed to the valence electron concentration (e/a) and the unit-cell volume of the high-temperature phase. With increasing transition temperatures (or e/a), the resultant martensitic crystal structure evolves in a sequence of 4O → 10M → 14M → L1₀ in bulk Ni–Mn–Sn alloys.     

Synthesis of CaNi1−xPdx (0.1≤x≤1) alloys and hydrogenation properties of CaPd

An evaluation of the substitution of a third element for the constituent elements (Ca, Ni) in the compound was conducted in order to obtain information about stabilization of the CaNi compound which does not exist as a stable phase. Prior to the experimental study of the substitution, the candidates for the third element were investigated using Miedema’s semi-empirical model, from the standpoint of formation enthalpy, and as a result, Pd was chosen as the element to stabilize the compound. The samples with the nominal compositions of CaNi_1−xPd_x (0.1≤x≤1) were prepared by sintering and high frequency heating, and the constituent phases and hydrogenation properties were examined. New ternary phases such as Ca₁(Ni, Pd)₁ were not obtained under the present conditions; however, some pieces of new information such as the substitution of Ni for Pd in CaPd₂ and reversible hydrogenation of CaPd at 373 K were obtained through the studies.     

CuCr_(1-x)Mg_xO_2(0≤x≤0.09)薄膜的光电性能

采用射频磁控溅射方法,在石英衬底上制备Mg掺杂的CuCrO2薄膜。通过XRD、紫外吸收光谱及电学性能的测量表征该系列薄膜样品的结构与光电性能。结果表明:退火处理后所有薄膜样品的结晶性良好,均为3R型铜铁矿结构;薄膜的电导率随掺杂量的增加而增大。当x=0.09时,样品的室温电导率可达6.16×10-2S/cm,比未掺杂的CuCrO2提高近400倍,且霍耳测试表明所制备的薄膜为p型导电体。电导率随温度变化关系表明:薄膜样品在200～300K的温度范围内均很好地符合Arrhenius热激活规律;当x=0.09时,最低激活能仅为0.034eV。薄膜的可见光透过率与光学带隙宽度均随掺杂量的增加而减小。     

Ni52Mn21+xGa27-x(x=0-5)磁性形状记忆合金的相变

研究了非化学计量成分的多晶Ni52Mn21+xGa27-x(x=0-5)系列合金的热弹性马氏体相变和磁相变.合金的马氏体相变温度Ms随Mn含量的增加而升高,当x＞4时,Ms已经升高到室温以上,而马氏体相变滞后△T随z的增大而减小;合金的磁相变温度TC随z增加而升高,但变化范围不大,在z＞2后,Tc保持在348 K左右.实验获得了一种具有实用前景的合金成分--Ni52Mn25Ga23合金,其马氏体相变温度在室温以上,相变滞后仅为5 K.     

Exchange-bias reversal in Mn2−xNi1+xGa films with antisite disorder

We report on the exchange-bias reversal in Mn_2−xNi_1+xGa (x = 0, 0.2, 0.4, and 0.6) thin films grown by molecular beam epitaxy on GaAs substrates. Exchange bias reversal is observed in these intrinsically ferrimagnetic films together with a reduction in the total moment even under increasing of Ni content which usually increases the total moment. These magnetic features indicate that antisite disorder is responsible for engender changes in the exchange-bias and total moment. Density functional theory calculations were performed to determine the magnetic moment dependence with the volume of cubic austenite and tetragonal martensite structures. A simple phenomenological approach is used to extract an effective exchange coupling constant from exchange bias fields.     

Ce1-xNdxO2-x/2(0≤x≤0.6)纳米粉体的低温燃烧合成

采用低温燃烧合成法,在柠檬酸-硝酸盐体系中合成了Ce1-xNdxO2-x／2（0≤x≤0.6）固溶体纳米粉体．X射线衍射（XRD）结果表明,Nd^3＋取代Ce^4＋形成具有单相立方萤石结构的固溶体,其晶格常数随Nd^3＋掺杂浓度的增大而线性增加,晶粒尺寸在15-24am之间．透射电镜（TEM）结果表明,粉体颗粒尺寸在2m-40am之间,分散性较好,具有较高的烧结活性．Raman光谱结果表明,F2g宽化峰的出现与掺杂后固溶体中产生的氧空位有关,并且随着掺杂浓度的增加,氧空位数量也随之增加．X射线荧光光谱（XRF）的分析表明,实际掺杂浓度非常接近原始化学计量比．     

CRYSTAL STRUCTURE AND ELECTROCHEMICAL PROPERTIESOF Zr(Mn1-xNix)2(0.40≤x≤0.75) HYDROGEN STORAGE ALLOYS

1. IntroductionAmong the binary alloys ZrMZ (M=V,Cr,Mn,Fe,Co,Mn etc.), ZrVZ and ZrCrZ all?Xscan absorb a large quantity of hydrogen to form hydride as ZrVZH6 and ZrCr,H..,[1].The effects of V or Cr atom sites substituted by nickel atom on the crystal structure andelectrochemical properties of the binary ZrVZ or ZrCrZ alloys were investigated extensivelydue to the higher hydrogen storage in binary alloys[Z13]. Many high-performance ABZ typeLaves phase electrode alloys based on Zr…     

Magnetic and magnetocaloric properties in Cu-doped high Mn content Mn50Ni40−xCuxSn10 Heusler alloys

The effects of Cu substitution on the phase transitions and magnetocaloric effect of Mn₅₀Ni_40−xCu_xSn₁₀ Heusler alloys were investigated. With the increase of Cu content, the martensitic transformation (MT) temperature shifts substantially towards lower temperature, while the Curie temperature of austenite remains almost unchanged. The reverse MT temperature decreases from 180 to 171 K for Mn₅₀Ni₃₉Cu₁Sn₁₀ alloy as the magnetic field increases from 1 to 30 kOe. Under an applied magnetic field of 30 kOe, the maximum values of magnetic field induced entropy changes are 19.6, 28.9, and 14.2 J/kg K for x = 0, 1, and 2, respectively. The effective refrigerant capacities and hysteresis losses for these alloys were discussed in this paper.     

Phase transformations,inverse magnetocaloric effect and critical behavior of Ni50Mn36Sn14−xSix Heusler alloys

The magnetic, magnetocaloric and critical behavior properties are systematically investigated for the Heusler alloy system Ni₅₀Mn₃₆Sn_14−xSi_x (x=1, 2 and 3). For all the samples both the normal and inverse magnetocaloric effects (MCE) are observed. The magnetic entropy change and relative cooling power are evaluated near the structural phase transformation and magnetic transition regions under an applied magnetic field of 50 kOe. The maximum magnetic entropy change associated with the martensitic transition are 3.4 J kg⁻¹ K⁻¹, 2.5 J kg⁻¹ K⁻¹ and 1.3 J kg⁻¹ K⁻¹ for x=1, 2 and 3 respectively. The entropy change for x=1, 2 and 3 alloys near the Curie temperature of the austenite phase is found to be −2.8 J kg⁻¹ K⁻¹, −2.7 J kg⁻¹ K⁻¹ and −2.3 J kg⁻¹ K⁻¹ respectively. Relative cooling power is calculated in the vicinity of the Curie temperature of the austenite phase, as well as in the martensitic transition temperature regime. The critical parameters (β, γ and δ) of the samples were determined from the static magnetic data at the second-order ferromagnetic-paramagnetic transition region using the field dependence of magnetic entropy change.     

Sb掺杂Mg_(2-x)Zn_xSi(0≤x≤0.1)固溶体的热电性能（英文）

利用B_2O_3助熔剂法结合SPS技术制备了Mg_(2-x)Zn_xSi_(0.99)Sb_(0.01)(0≤x≤0.1)固溶体。测量了300~780 K温度区间内试样的电导率、塞贝克系数和热导率。发现晶格热导率随Zn取代量的增大而降低。而电导率随Zn取代量的增大而先降低后增大。讨论了影响电导率与晶格热导率的变化规律的具体内在机制。所有样品中x=0.075样品的功率因子最高,在780 K达1.76 m W·m~(-1)·K~(-2),比基体Mg_(2-x)Zn_xSi_(0.99)Sb_(0.01)高约18%。x=0.1样品具有最低晶格热导率,在770 K达到2.86 W·m~(-1)·K~(-1)。低晶格热导率使Mg_(1.9)Zn_(0.1)Si_(0.99)Sb_(0.01)具有最高热电优值,在780 K达0.37。     

Phase Stability,Magnetic Properties,and Martensitic Transformation of Ni2−xMn1+x+ySn1−y Heusler Alloy with Excess Mn by First-Principles Calculations

The phase stability, magnetic properties, martensitic transformation, and electronic properties of the Ni_2−xMn_1+x+ySn_1−y system with excess Mn have been systematically investigated by the first-principles calculations. Results indicate that the excess Mn atoms will directly occupy the sublattices of Ni (Mn_Ni) or Sn (Mn_Sn). The formation energy (E_f) of the austenite has a relationship with the Mn content: E_f = 135.27(1 + x + y) − 293.01, that is, the phase stability of the austenite decreases gradually with the increase in Mn content. According to the results of the formation energy of austenite, there is an antiparallel arrangement of the magnetic moment between the excess and normal Mn atoms in the Ni_2−xMn_1+x+ySn_1−y (x = 0 or y = 0) system, while the magnetic moment direction of the normal Mn atoms arranges antiparallel to that of Mn_Ni atoms and parallel to that of Mn_Sn atoms in the Ni_2−xMn_1+x+ySn_1−y (x, y ≠ 0) system. The martensitic transformation occurs in some Ni_2−xMn_1+x+ySn_1−y (x, y ≠ 0) alloys with large magnetic moments of ferrimagnetic austenite. Besides, the valence electrons tend to distribute around the Ni or Mn_Ni atoms and mainly bond with the normal Mn atoms. The results of this work can lay a theoretical foundation for further development of the Ni_2−xMn_1+x+ySn_1−y system as the potential ferromagnetic shape memory alloys.     

Effects of Mn Content on Mechanical Properties of FeCoCrNiMn_x (0≤x≤0.3) High-Entropy Alloys: A First-Principles Study

Effects of Mn content on mechanical properties of FeCoCrNiMn_x(0 ≤x≤0.3) high-entropy alloys(HEAs) are investigated via first-prmciples calculations combining EMTO-CPA method.Related physical parameters,including lattice constant.elastic constants,elastic modulus,Pugh's ratio,anisotropy factors,Poisson's ratio,Cauchy pressure,Vickers hardness,yield strength,and energy factor,are calculated as a function of Mn content.The results show that the resistances to bulk,elastic,and shear deformation decrease with increasing Mn content.Pugh's ratio B/G indicates that the ductility of FeCoCrNiMn_x HEAs has a remarkable reduction between 22 and 24% of Mn content.Meanwhile,Cauchy pressure suggests that the atomic bonding transforms from metallic to directional characteristic from 22 to 24% of Mn content.Vickers hardness and yield strength of FeCoCrNiMn HEA are intrinsically larger than those of FeCoCrNi HEA.Dislocation nucleation easily occurs in FeCoCrNiMn HE A compared to FeCoCrNi HEA,and large dislocation width in FeCoCrNiMnO_2 HE A results in low stacking-fault energy,which easily induces twinning deformation.This work provides a valuable msieht for further theoretical and experimental study on the mechanical properties of FeCoCrNiMn_x(0≤x≤0.3) HEAs.