Microstructure evolution of laser solid forming of Ti-Al-V ternary system alloys from blended elemental powders

Morphology evolution of prior β grains of laser solid forming (LSF) Ti-xAl-yV (x 11,y 20) alloys from blended elemental powders is investigated. The formation mechanism of grain morphology is revealed by incorporating columnar to equiaxed transition (CET) mechanism during solidification. The morphology of prior β grains of LSF Ti-6Al-yV changes from columnar to equiaxed grains with increasing element V content from 4 to 20 wt.-%. This agrees well with CET theoretical prediction. Likewise, the grain morphology of LSF Ti-xAl-2V from blended elemental powders changes from large columnar to small equiaxed with increasing Al content from 2 to 11 wt.-%. The macro-morphologies of LSF Ti-8Al-2V and Ti-11Al-2V from blended elemental powders do not agree with CET predictions. This is caused by the increased disturbance effects of mixing enthalpy with increasing Al content, generated in the alloying process of Ti, Al, and V in the molten pool.     

Co50Fe25-xMnxSi25系列合金的结构、磁性和半金属性研究

利用实验和能带计算相结合的方法,对介于两种预期的半金属Heusler合金Co₂FeSi和Co₂MnSi间的四元合金Co₅₀Fe_25-xMn_xSi₂₅的晶体结构、磁性、能带结构和半金属性进行了研究.采用考虑库仑相互作用的的广义梯度近似方法计算了系列合金的能带结构,通过与实验结果进行对比,揭示了成分变化过程中合金分子磁矩及原子磁矩的变化规律.研究发现, 关键词： 磁性 半金属 Heusler合金     

Half-Heusler合金NiFeSb和NiMnSb的磁性及电子结构的第一性原理研究

用基于密度泛函理论的第一性原理方法,计算了half-Heusler合金NiFeSb和NiMnSb的晶体结构、磁性及电子结构。计算结果表明,磁性原子Fe和Mn在两种合金的总磁矩中贡献最大,在NiFeSb总磁矩中,Ni原子贡献比例接近在NiMnSb中的2倍,而Sb原子的贡献比例是在NiMnSb中的1/5;两种合金的自旋向上能带都具有明显的金属特征,而自旋向下能带有明显的差别;两种合金费米能级以下的总态密度(DOS)主要由Ni-3d 和Fe-3d（Mn-3d）态决定,费米能级以上主要由Fe-3d（Mn-3d）自旋向下部分决定。     

Co2YSn(Y=Ti,Zr)电子结构和轨道磁性的第一性原理研究

基于密度泛函理论(DFT)采用第一性原理的全势能线性缀加平面波(FLAPW)的能带计算方法研究了强磁性Heusler合金Co2TiSn和Co2ZrSn的电子能带结构,在计算中考虑了自旋-轨道藕合(SOC)的修正.计算结果表明两种合金在费米面附近的能带结构是一个d-d电子杂化作用形成的能带.分析计算结果发现Co原子对磁矩有主要的贡献,两种Heusler合金的磁矩是由于Co原子3d eg的自旋劈裂形成的,3deg的自旋向下分量是合金的电子态密度(DOS)的主要来源.由能带计算得到Co2TiSn和Co2ZrSn的自旋磁矩分别为1.97μB和1.96μB,其中Co原子在上述两种合金中的自旋磁矩分别是1.01μB和1.02μB,轨道磁矩分别为0.041μB和0.051μB.     

A simulation study of microstructure evolution during solidification process of liquid metal Ni

A molecular dynamics simulation study has been performed for the microstructure evolution in a liquid metal Ni system during crystallization process at two cooling rates by adopting the embedded atom method (EAM) model potential. The bond-type index method of Honeycutt--Andersen (HA) and a new cluster-type index method (CTIM-2) have been used to detect and analyse the microstructures in this system. It is demonstrated that the cooling rate plays a critical role in the microstructure evolution: below the crystallization temperature $T_{\rm c}$, the effects of cooling rate are very remarkable and can be fully displayed. At different cooling rates of $2.0\times10^{13}$\,K\,$\cdot$\,s$^{-1}$ and $1.0\times10^{12}$\,K\,$\cdot$\,s$^{-1}$, two different kinds of crystal structures are obtained in the system. The first one is the coexistence of the hcp (expressed by (12 0 0 0 6 6) in CTIM-2) and the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 and 1422 bond-types, and the hcp basic cluster becomes the dominant one with decreasing temperature, the second one is mainly the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 bond-type, and their crystallization temperatures $T_{\rm c}$ would be 1073 and 1173\,K, respectively.     

应力导致InAs/In0.15Ga0.85As量子点结构中 In0.15Ga0.85As阱层的合金分解效应研究

利用固源分子束外延技术,在In0.15Ga0.85As/GaAs量子阱生长了两个InAs/In0.15Ga0.85As量子点(DWELL)样品.通过改变其中一个InAs DWELL样品中的In0.15Ga0.85As阱层的厚度和生长温度,获得了量子点尺寸增大而且尺寸分布更均匀的结果.结合光致发光光谱(PL)和压电调制光谱(PzR)实验结果,发现该样品量子点的光学性质也同时得到了极大的优化.基于有效质量近似的数值计算结果表明:量子点后生长过程中应力导致In0.15Ga0.85As阱层合金分解机理是导致量子点尺寸和光学性质得到优化的主要原因.     

Electron Transport in Ga-Rich InxGa1-xN Alloys

Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN （0.06 ≤ x ≤ 0.135） alloys grown by metal-organic vapour phase epitaxy （MOVPE） technique are carried out as a function of temperature （15-350 K）. Within the experimental error, the electron concentration in Inx Ga1-x N alloys is independent of temperature while the resistivity decreases as the temperature increases. Therefore, Inx Ga1-xN （0.06 ≤ x ≤0.135） alloys are considered in the metallic phase near the Mort transition. It has been shown that the temperaturedependent metallic conductivity can be well explained by the Mort model that takes into account electron-electron interactions and weak localization effects.     

Formation of Pd-Ni Based Bulk Metallic Glasses

Bulk metallic glasses are prepared in Pd4o.sNi4o.sSixP19-x （x = 0-14 at.%） alloys by a combination of flux treatment and water quenching technique. It is found that the thermal stability of the Pd4o.sNi4o.sSixP19=x glassy alloys depends on the addition of Si content. Among the Pd4o.sNi4o.sSixP19=x glassy alloys studied, the Pd4o.sNi4o.sSisPls bulk metallic glass exhibits the largest supercooled liquid region （△T = 119 K） and the highest activation energy of crystallization （283.3k J/tool）, showing enhanced glass formation ability and extraordinary glassy thermal stability.     

在合金Fe1—yCoySi中一种新的磁电阻微观机制

在混价锰氧化物巨磁电阻材料中[例如,(Ｌａ,Ｃａ)ＭｎＯ3],材料的金属性来源于掺杂,而材料的磁性(局域磁矩)原本就存在于母化合物(ＬａＭｎＯ3)中,磁性的载体是Ｍｎ离子内能量较低的三个ｄ电子(ｔ2ｇ电子).外加磁场迫使传导电子的自旋与局域矩趋于平行,减小了传导电子在格点间跳转的库仑能,从而导致负的磁电阻效应,即外加磁场使电阻减小.此外,也有的材料表现出正的磁电阻效应,其中可能涉及各种各样的机制:(1)电子在磁场中由于洛伦兹力的作用产生回旋运动,它增加了电子受散射的几率,从而导致电阻增大.上述机制仅发生在磁场平行于电场的情况下…     

高纯La-Ni-Al合金成分及杂质元素的分析方法研究

叙述了镧－镍－铝（La-Ni-Al)合金分镍、铝及微量杂质元素锌、铁、锰、镁、硅、铜和钙的ICP－AES测定方法。样品以HNO3（1＋1）溶解,稀释后直接测定主量元素镍和铝;用基体匹配法补偿基体效应测定其他杂质元素。各元素回收率在95％－106％,相对标准偏差优于5％。