Transport properties on Sn-filled and Te-doped CoSb<Subscript>3</Subscript> skutterudites

Sn-filled and Te-doped CoSb₃ skutterudites (Sn_xCo₈Sb_23.25Te_0.75) were synthesized by the encapsulated induction melting process. Single δ-phase was successfully obtained by subsequent heat treatment at 823 K for 6 days. Structural characterizations were carried out through X-ray diffraction studies. Transport properties such as the Seebeck coefficient, electrical resistivity, thermal conductivity, carrier concentration and mobility were measured and analyzed. The unfilled Co₈Sb_23.25Te_0.75 sample showed n-type conductivity from 300 K to 700K. However, the Sn-filled Sn_xCo₈Sb_23.25Te_0.75 showed n-type conductivity for z=0.25 and 0.5, and p-type conductivity for z=1.0 and 1.5 from 300 K to 700 K. Thermal conductivity was reduced by the impurity-phonon scattering. The dimensionless figure of merit (ZT) was remarkably improved over that of untreated CoSb₃. However, the ZT value decreased when filling with z≥1.0 because the conductivity type was changed from n-type to p-type, thereby allowing bipolar conduction. The details are discussed in terms of the two-band model and the bipolar thermoelectric effect.     

Electronic transport properties of Ni-doped CoSb<Subscript>3</Subscript> prepared by encapsulated induction melting

Ni-doped CoSb₃ skutterudites were prepared by encapsulated induction melting and their thermoelectric and electronic transport properties were investigated. The negative signs of Seebeck and Hal coefficients for all Ni-doped specimens revealed that Ni atoms successfully acted as n-type dopants by substituting Co atoms. The carrier concentration increased as the Ni doping content increased, and the Ni dopants could generate excess electrons. However, the carrier mobility decreased as the doping content increased, which indicates that the electron mean free path was reduced by the impurity scattering. The Seebeck coefficient and the electrical resistivity decreased as the carrier concentration increased, as the increase in carrier concentration by doping overcame the decrease in the carrier mobility by impurity scattering. The Seebeck coefficient showed a negative value at all temperatures examined and increased as the temperature increased. The temperature dependence of electrical resistivity suggested that Co_1−xNi_xSb₃ is a highly degenerate semiconducting material. Thermal conductivity was considerably reduced by Ni doping, and the lattice contribution was dominant in the Ni-doped CoSb₃.     

Thermoelectric properties of In<Subscript>z</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> skutterudites

In this study, indium-filled CoSb₃ skutterudite is synthesized via encapsulated induction melting and subsequent annealing at 823 K for six days, and the crystal structure, lattice constant, filler position, phase homogeneity and stability were investigated. All of the In-filled CoSb₃ samples were n-type conducting samples. The temperature dependence of the electrical resistivity showed In_zCo₄Sb₁₂ is a highly degenerate semiconducting material. The thermal conductivity was reduced considerably by In filling. The highest thermoelectric figure of merit value was achieved when the In filling fraction is 0.25. It was found that the ZT of the In-filled CoSb₃ (In_zCo₄Sb₁₂) was higher than that of the In-substituted CoSb₃ (Co_3.75In_0.25Sb₁₂ and Co₄Sb_11.75In_0.25). This is mainly due to the lower thermal conductivity and higher Seebeck coefficient.     

Properties of Co-doped N-type FeSi2 processed by mechanical alloying

Iron-silicide was produced with a mechanical alloying process and consolidated through vacuum hot pressing. The as-milled powders were of metastable state and fully transformed into the ß-FeSi₂ phase through subsequent isothermal annealing. The as-consolidated iron silicides consisted of an untransformed mixture of α-Fe₂Si₅ and ?-FeSi phases and a partially transformed β-FeSi₂ phase was found in the low density compact. Isothermal annealing was carried out to induce transformation into a thermoelectric semiconducting β-FeSi₂ phase. The transformation behavior of the β-FeSi₂ was investigated utilizing DTA, SEM, and XRD analyses. Isothermal annealing at 830°C in vacuum led to a thermoelectric semiconducting β-FeSi₂ phase transformation, but some residual metallic α and ?-phases were unavoidable even after 96 hours of annealing. The iron silicide microstructures were investigated using SEM and TEM. The mechanical and thermoelectric properties of the β-FeSi₂ materials before and after isothermal annealing are characterized in this study.     

机械合金化制备Cu-0.5Wt%Nb合金组织与性能的研究

采用机械合金化法制备了Cu-0.5wt％Nb纳米弥散强化铜合金。通过金相、透射电镜观察了该合金粉末态、冷轧态及不同温度退火后合金的组织结构变化。通过测量该合金不同状态的硬度及相对电导率,实验结果表明,其冷轧态硬度较高(可达160kg/mm2),随退火温度升高硬度呈缓慢下降趋势;900℃退火后,硬度仍可达91kg/mm2,表明此合金抗高温软化性能较好.此外该合金相对电导率最高可达89% IACS,这进一步说明利用机械合金化法制备的Cu-0.5wt%Nb合金具有优越的综合性能.     

机械合金化法制备Al—Cu—Fe纳米非晶合金

采用行星式高能球磨机制备了Al80-xCuxFe20(x=20-40）三元非晶纳米合金粉末,分析了不同球磨时间及热处理工艺对粉末结构、颗粒大小等的影响。结果表明：成分为Al40Cu40Fe20的粉末球磨时逐步非晶化,球磨33h后,非晶化程度最大,最小颗粒尺寸达到5．6nm;进一步球磨,非晶晶化,颗粒尺寸增大;成分为Al80-xCuxFe20(x=20,25,30)的粉末球磨90h后,得到非晶,最小颗粒尺寸为3．4nm。球磨制备的Al-Cu-Fe非晶粉末具有铁磁性。用DSC测量了其晶化温度（Tc),Tc≈873℃。     

合金元素对单相渗碳体磁性粉体制备及性能的影响

通过机械合金化和真空退火热处理的方法制备了单相渗碳体粉末,并结合第一性原理计算,分析了Mn、Cr和Si对合金渗碳体的成相能力及渗碳体磁学性能的影响.结果表明,机械合金化+600℃真空热处理可获得单相渗碳体.Si的加入完全抑制了渗碳体的生成,而加入Mn、Cr对渗碳体生成有促进作用.Cr、Mn合金化的渗碳体的粉末饱和磁化强...     

机械合金化法制备金锡合金

采用高能球磨机械合金化法制备了Au-20%Sn合金,分析了合金物相、组织和硬度随球磨时间的变化规律,探讨了合金塑性与合金组织及制备工艺的关系。结果表明:采用高能球磨机械合金化法可以制备Au-20%Sn合金;随球磨时间的增加,Au-20%Sn的合金化程度增加,组织中的金属间化合物逐渐增多,最终基本上为δ相和ζ′相;合金的硬度随球磨时间的延长逐渐升高,并在球磨60min后获得最高硬度104.2HV,然后开始下降;球磨后的合金粉末在190℃×2h的烧结过程中发生了不同程度的再结晶和晶粒长大,再结晶程度随球磨时间的延长而增加,导致烧结后合金硬度在球磨时间超过60min后反而下降。     

Carbon solubility in Cu-based composite prepared by mechanical alloying

The powder mixture of Cu and graphite was mechanically alloyed （MA） in an oscillating type ball mill. The milling time was varied in order to investigate its influence on the microstructural evolution of mechanically alloyed powders. The phase constituent, alloying characteristics, grain size and lattice distortion of these powders were determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The results show that the C is confirmed to dissolve in the Cu lattice, forming solid solution of carbon in copper the lattice parameter of copper increases with carbon concentration increasing, up to a saturation value of about 4%C（mass fraction）. Higher ball-mill energy is beneficial for twins and nanograin formation.     

机械合金化制备AgCu20Ni2合金的组织和性能

研究了机械合金化诱发AgCu20Ni2过饱和合金粉末的形成及粉末冶金方法制备AgCu20Ni2合金的过程,对获得的AgCu20Ni2合金的组织和物理性能关系进行了分析,探讨了制备工艺和冷压变形对合金综合性能的影响。结果表明：采用高能球磨30 h,可获得纳米晶的过饱和合金粉末;合金粉末制备的AgCu20Ni2合金由富Ag的基体α相和均匀分布的析出β相构成,析出相界面结构能有效阻碍基体中位错的运动,强化效果明显。合金断口的SEM、EDS分析表明,AgCu20Ni2合金的断裂类型为韧性断裂。     

Influence of process control agent on interdiffusion between Al and Mg during mechanical alloying

The influence of a process control agent (PCA) on the reaction rate during mechanical alloying has been studied. Mechanical alloying of Al–Mg powder mixtures with different PCAs was carried out using a planetary ball mill. X-ray diffraction spectra showed that a small amount of PCA might lead to fast interdiffusion and reaction between Al and Mg although the crystalline sizes were in general the same for the powders when using different amounts of PCA. The fast interdiffusion and advanced reaction are closely associated with the diffusion distance between the powder particles due to the presence of PCA and to the actual weight ratio of ball to powder.     

Synthesis and characteristics of W-Ni-Fe nano-composite powders prepared by mechanical alloying

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Microstructure and properties of mechanical alloying particles reinforced aluminum matrix composites prepared by semisolid stirring pouring method

Aluminum matrix composites reinforced with mechanical alloying particles(SiC_p) were fabricated by the semisolid stirring pouring method. The inf luence of mechanical alloying particles and Mg on the microstructure and mechanical properties of the composites was investigated by means of optical microscopy(OM), X-ray diffraction scanning(XRD), electron microscopy(SEM) and energy dispersive spectroscopy(EDS). Results show that the addition of Mg converts the agglomerate mechanical al oying particles in ZL101 matrix composites into dispersed distribution in ZL101-Mg matrix composites, large matrix grains into f ine equiaxed matrix grains, and eutectic phase into f ine particles. So the mechanical properties of ZL101-Mg matrix composites are better than those of ZL101 matrix composites. The mechanical properties of ZL101/ZL101-Mg matrix composites are gradually increased with the increase of the volume fraction of mechanical alloying particles. When the volume fraction of mechanical alloying particles is 3%, the Vickers hardness and ultimate tensile strength of the ZL101/ZL101-Mg matrix composites reach their maximum values.     

机械合金化-热压制备Nb/NbCr2复合材料的组织与性能

采用机械合金化与热压工艺制备以Nb固溶体为软第二相的Laves相Nb/NbCr2复合材料。研究不同成分的Nb、Cr元素粉经20 h球磨后在1 250℃,0.5 h热压工艺下所获得的Nb/NbCr2复合材料的组织和性能。结果表明：随着偏离Laves相化学配比的Nb含量的增大,材料的致密度、抗压强度、塑性应变均增加,而维氏硬度减小。Laves相含量为29%的Cr-77.5Nb合金的组织均匀,Nb固溶体与Laves相间隔分布,晶粒尺寸达到亚微米级,屈服强度为2 790 MPa,抗压强度为3 174 MPa,塑性应变达到5.44%,充分实现了细晶和软第二相综合增韧的效果。     

Complete flux jumping in nano-structured MgB2 superconductors prepared by mechanical alloying

High density nano-crystalline MgB₂ bulk superconductors with induced pinning centres were prepared from elemental precursors by a sequence of ball milling, heat treatment, and final pressing. The XRD results revealed the main phase was MgB₂ with a minor component of MgO. The magnetic moment versus temperature indicated that the transition temperature of MgB₂ samples was around 34 K, which is less than the typical transition temperature of commercial powders and also the transition temperature strongly depended on the milling time. It is well known that introduction of defects, grain boundaries and impurities act as effective flux pinning centres in MgB₂ and results in increased critical current density, J_c and decreased the transition temperature, T_c. The magnetization measurements were performed using VSM at 10 K, 20 K and 30 K, and the M–H curves indicated a complete flux jump effect, which is a severe problem for the application of superconductors. It was determined that a noticeable amount of heating (0.3 K jumps at 10 K) occurs at these jumps. In addition, it was found that the sweeping rate of magnetic field and the size of bulk sample are very effective to promote the flux jumping and whereas a low sweeping rate (12 Oe/s) avoids these “avalanches”, consistent with a kind of supercritical phenomenon: going slower allows the field gradients to stay close enough to equilibrium so that the avalanche effect is not triggered. In contrast, the sweeping rate of 100 Oe/s leads to numerous jumps.     

机械合金化法制备不同Cr含量的W-Cr纳米合金粉末

采用机械合金化法制备Cr含量为8%、12.5%、20%（质量分数）的纳米W-Cr合金粉,对不同球磨时间粉末进行X射线衍射分析,以确定物相、晶粒尺寸及微应变,并采用扫描电子显微镜观察粉末形貌及粒度的变化。结果表明,采用机械合金化法可以制备不同Cr含量的纳米W-Cr合金粉。随着Cr含量的增加,制备纳米W-Cr合金粉所需球磨时间越长,其中W-8%Cr、W-12.5%Cr和W-20%Cr粉末的最佳球磨时间分别为72、84和96 h,晶粒尺寸小于30 nm。随着球磨时间的增加,晶粒尺寸不断减小,微应变逐渐增加,使常温下Cr在W中的固溶度增加,形成W的过饱和固溶体。Cr含量不同的W-Cr粉末完全合金化均经过4个阶段。     

Electrochemical hydrogen storage properties of La0.95Mg2.05Ni9 alloy prepared by mechanical alloying

1　INTRODUCTIONTheMg basedhydrogenstoragealloysastheac tivematerialsofmetalhydrideelectrodeshaveattract edattentionbecauseofhighertheoreticalcapacitiesforhydrogenabsorption/desorption ,andthelowerpricecomparedwiththeotherhydrides[17] .Recent ly ,thecharge dischargepropertiesofMg basedalloysatroomtemperaturehavebeengreatlyimprovedbysomeresearchers[813] .Inparticular ,theMg Ni REsystemalloyisoneofthemost promisinghydrides[14 16 ] .Tanakaetal[15] reportedthatthenanocrystallineMg Ni RE(R…     

Structure and magnetic properties of Fe-based powders prepared by mechanical alloying

FeSiAlCr alloy powders were prepared by mechanical alloying, the milling time were 20 h, 40 h, 60 h and 80~h, respectively. Powders morphology was studied by SEM. Microstructure of powders milled for various times were analyzed by XRD. The complex permittivity and complex permeability of four powders were tested in the frequency range from 0.5 to 18 GHz, and their microwave absorption properties were analyzed. It was found that the particle size of powders milled for 80~h was less than 2μm. Silicon and aluminum atoms were dissolved into the crystal lattice of iron, and chromium atoms can form alloy with iron atoms. The minimum peak value of reflectivity can reach to -11.3 dB at the frequency of 4.3 GHz for 80 h milling powders, and the other one was -6 dB at 16.5 GHz.     

Ageing behavior of Cu-15Ni-8Sn alloy prepared by mechanical alloying

1INTRODUCTIONCu-Ni-Snal1oyshavebeenconsideredaspossiblesubstitutesforCu-Bealloysinthemanu-factureofc0nnectors,springcomponentsandsoforth,intheelectronicsindustriesbecauseoftheiroutstandingpropertiessuchashighstrength,highelasticmodulus,exce1lenterosi0nresistanceandhighresistancetostressrelaxationatelevatedtemperature['].Inaddition,com-paredwithCu'Bealloys,thelowcostandminorpollutioninthepreparationprocessofthealloyhavealsoattractedtheincreasingattentionofmanyresearchers.However,extensiv…