液态Ca70Mg30合金快速凝固过程中纳米团簇结构形成演变特性模拟

采用分子动力学方法对液态Ca70Mg30合金快速凝固过程中纳米团簇结构的形成和演变特性进行模拟。采用原子团类型指数法(CTIM)对凝固过程中纳米团簇结构的演变进行分析。结果表明：系统在5×1011 K/s的冷速条件下形成以1551、1541和1431为主的非晶态结构,非晶转变温度约为530 K;(120120)二十面体基本原子团对系统非晶结构的形成起到决定性的作用,并且原子半径较小的Mg原子更容易占据二十面体基本原子团中心原子的位置;同时,纳米团簇主要是通过中等尺寸团簇的合并而形成,纳米级大团簇的形成演变过程呈现出类似于非晶晶化过程的3个阶段式的变化。     

Nb、Ta等元素对Zr基大块非晶非晶形成能力及耐腐蚀性影响机理研究

  用计算机编程构造了Zr基非晶合金包含二十面体原子团簇的Zr₂Ni晶体相.用Zr₂Ni晶体相中以Ni原子为中心的二十面体原子团簇模拟Zr基非晶中二十面体团簇.应用实空间的递归方法计算了合金元素取代二十面体原子团簇中心和顶角位置原子时的局域态密度、二十面体原子团簇中中心Ni原子与其近邻合金元素Nb、Ta、Ti、V的总键级积分及团簇的费米能级.结果表明,Nb、Ta、Ti和V取代Zr原子后使其与Ni的键级积分有所降低,使合金的非晶形成能力下降,但Nb、Ta对合金的非晶形成能力影响不大;Nb、V取代Zr使费米能级升高,可使Zr基非晶容易钝化,提高耐蚀性;Ta对Zr基非晶的耐蚀性影响不大.而Ti使Zr基非晶的钝化能力下降.综合合金元素对非晶形成能力和耐腐蚀性的影响,Nb是最有益的合金元素,即在Zr基非晶中,通过加入少量的Nb元素,可以制备出具有较高耐腐蚀性的大块非晶.     

Cu-50%Ni合金快速凝固过程中原子团簇演变的分子动力学模拟

采用NPT分子动力学模拟方法,应用周期边界条件,模拟了Cu-50％Ni(原子分数)合金熔体在不同冷却过程中原子团簇的演变情况,给出了以1×1014K/s冷速冷却至室温时Cu-50％Ni非晶体系中存在的各种结构单元,并研究了Cu,Ni原子在这些结构单元中的排列情况.结果表明,较高冷速下形成的非晶具有较高的能量和较高的非晶转变温度(Tg).在冷却过程中,原子间的短程作用逐渐加强,PCF图第一峰值逐渐增大. 1551键对在非晶体系中占主导地位,且受冷速影响较大.体系中除了正二十面体外,还存在着各种缺陷多面体,其中含1551键对较多的缺陷多面体其数目也较多. FK多面体与Bernal多面体数目始终很少.大原子(Cu)易于占据多面体顶点,而小原子(Ni)则倾向于占据各多面体中心较大的空隙.随着冷速的降低,各多面体数目均有不同程度的下降.     

冷却速度对快凝Cu_(56)Zr_(44)合金二十面体团簇化的影响（英文）

采用分子动力学方法模拟研究液态Cu56Zr44合金不同冷速(γ)下的快速凝固过程。为了评估冷速对二十面体团簇化趋势与致密化程度的影响,采用十指数的团簇类型指数方法表征过冷液体和快凝固体的局域原子结构。利用二十面体团聚度(fI)和化学序参数(ηαβ)以及致密化系数(D0,DI和DIS)分别对其团簇化和有序度以及二十面体团簇密堆积度进行评估。结果表明,Cu56Zr44合金系统中主要的局域原子结构为Cu心的Z12团簇,其中大多数是(12 0 12 0 0 0 0 0 0 0)规则二十面体和(12 0 8 0 0 0 2 2 0 0)及(12 2 8 2 0 0 0 0 0 0)缺陷二十面体。在Tg以下,二十面体基本团簇以IS铰链(二十面体键)结合成二十面体中程序(IMRO),其数目N、尺寸n、序参数ηαβ和空间分布随γ而变化。在玻璃转变的临界冷速γc以上,较低的冷速有利于二十面体数目的增加和IMRO尺寸的增大。同时,较慢的冷却过程有助于快凝固体中IMRO堆积密度的增加和二十面体团簇化程度的提高。     

液态金属铜Cu凝固过程中团簇结构的形成以及成核生长特性的模拟

采用分子动力学方法和Quantum Sutton-Chen多体势,对2万个液态金属铜(Cu)原子在两个不同冷速凝固过程中其微观团簇结构的形成特性以及晶体的成核生长进行模拟。运用双体分布函数、Honeycutt-Andersen(HA)键型指数法、原子团类型指数法(CTIM-2)和可视化分析等方法,对凝固过程中微观结构转变和原子团簇的微观结构演变特性进行分析。结果表明:冷却速率为4.0×1012 K/s和2.0×1012 K/s时,系统形成以1421、1422键型或由这两种键型构成的面心立方(FCC)(12 0 0 0 12 0)和六角密集(HCP)基本原子团(12 0 0 0 6 6)为主体的晶体结构;尤其是由1421键型构成的面心立方(12 0 0 0 12 0)基本原子团在晶体生长和对微观结构演变的影响占主导地位。两种冷却速度下的结晶温度分别为673 K和773 K,即冷却速度越慢,结晶温度越高;系统最终形成了由FCC和HCP组成的混合晶体结构,但以FCC晶体结构为主;FCC(12 0 0 0 12 0)基本原子团在慢速低温时具有较好的遗传特性,基本原子团之间很容易连接在一起构成较大的纳米级大团簇结构。     

一种新型Nd基块体非晶合金

在铜模铸造条件下制备了直径2．5mm的Nd61Fe30Zn9块状非晶合金．在普通DSC条件下，没有观察到这种合金的玻璃转变温度，晶化温度为730K，比Nd60Fe30Al10非晶合金的晶化温度低约70K，因此该合金的热稳定性较低．熔化行为分析表明，合金Nd61Fe30Zn9的熔化过程为单峰吸热过程，且熔化区间仅为54K，说明该合金的成分接近合金的共晶成分，但母合金的自然凝固组织不具有共晶凝固特点，表现为粗大的枝晶状组织．讨论了成分和组织对合金非晶形成能力的影响．     

二元液态金属AgxCu1-x快速凝固过程的分子动力学模拟研究

用quantum Sutton-Chen多体势对AgxCu1-x在冷却速率为2×1012K/s凝固过程的模拟,发现AgxCu1-x在x=35～65范围内具有形成非晶的能力,特别是对应于二元相图共晶点的Ag60Cu40在凝固过程中二十面体和其它多面体结构不仅数目大,而且还具有极为稳定的遗传性,而最容易得到非晶态合金.证实了合金化效应对非晶态合金的形成倾向和稳定性的关键作用.此外采用键对及原子多面体类型指数法对凝固过程中微观结构组态变化的分析,不但能说明二十面体结构在非晶态合金形成和稳定性中所起的关键作用,又有助于对液态金属的凝固过程、非晶态微观结构特征的深入理解.     

液态金属Ga的快速凝固模拟

采用分子动力学方法对液态Ga 的凝固过程进行了模拟研究. 结果表明, 与通常液态及非晶态金属相反, 随着温度降低, 与二十面体相关的1551键型数越来越少, 而与菱面体相关的1311, 1301和1201键型数目显著增加, 最后形成以菱面体结构单元为主的非晶态结构. 以1.69×1012K/s的速度冷却时, 得到非晶态结构; 以1.01×1011K/s的速度冷却时, 发生晶化, 结晶转变温度约为144K.     

Ti100-xAlx合金快速凝固的分子动力学模拟

应用分子动力学对液态Ti100-xAlx(x=10,25,50,75,90)合金的快速凝固过程进行了模拟,并通过双体分布函数和HA键型指数法分析了凝固过程中熔体微观结构的演变特性.合金平均原子体积随温度变化的曲线表明,在5×1012 K/s冷速下,合金都形成了非晶结构;合金在降温过程中的双体分布函数显示出非晶的典型特征...     

Cu55Zr30Ti15非晶合金中纳米尺度成分分离区及其作用

为了研究大块非晶合金中成分分离区的存在状态及其在晶化过程中的作用，应用小角X射线散射技术（shxs）和差示扫描量热仪（DSC）研究Cu55Zr30Ti15非晶合金从310K到783K之间微结构的演化情况。实验发现在淬火状态下Cu55Zr30Ti15非晶合金中存在直径为55nm左右的成分分离区。非晶的结构弛豫包括659K之前的低温结构弛豫和659K到玻璃转变温度的高温结构弛豫。在玻璃转变温度到783K之间，观察到非晶基体中产生过渡相并转化为最终晶相的过程。表明成分分离区在晶化过程中有着重要作用，其驰豫所产生的有序原子团簇是随后晶化过程中晶核产生的基础。     

Simulation study on non-linear effects of initial melt temperatures on microstructures during solidification process of liquid Mg7Zn3 alloy

The non-linear effects of different initial melt temperatures on the microstructure evolution during the solidification process of liquid Mg₇Zn₃ alloys were investigated by molecular dynamics simulation. The microstructure transformation mechanisms were analyzed by several methods. The system was found to be solidified into amorphous structures from different initial melt temperatures at the same cooling rate of 10 × 10¹² K/s, and the 1551 bond-type and the icosahedron basic cluster (12 0 12 0) played a key role in the microstructure transition. Different initial melt temperatures had significant effects on the final microstructures. These effects only can be clearly observed below the glass transition temperature T_g; and these effects are non-linearly related to the initial melt temperatures, and fluctuated in a certain range. However, the changes of the average atomic energy of the systems are still linearly related with the initial melt temperatures, namely, the higher the initial melt temperature is, the more stable the amorphous structure is and the stronger the glass forming ability will be.     

Tb0.3Dy0.7Fe1.95-xTix（x=0,0.03,0.06,0.09）合金的微观组织与磁致伸缩性能

利用高真空非自耗电弧炉制备了Tb_0.3Dy_0.7Fe_1.95-xTi_x（x=0,0.03,0.06,0.09）合金,系统研究了不同Ti含量Tb_0.3Dy_0.7Fe_1.95-xTi_x合金的晶体结构、微观组织、磁致伸缩性能及它们之间的关系.结果表明:添加Ti后的Tb_0.3Dy_0.7Fe_1.95-xTi_x合金基体相仍为MgCu₂型Laves相结构,Ti取代了Tb_0.3Dy_0.7Fe_1.95合金中比其自身半径大的稀土原子Tb和Dy而使晶格常数减小.添加Ti后,初生相TiFe₂的形成使得凝固液体中富含R（R=Tb,Dy）从而抑制了有害相RFe₃的生成,Ti在基体相RFe₂中和富R相中都可溶解,分别形成了（R,Ti）Fe₂基体相和富（R,Ti）相.Ti的添加量对磁致伸缩性能的影响很大,当x=0.03时,Ti的添加使磁致伸缩性能较Tb_0.3Dy_0.7Fe_1.95母合金提高幅度最大,但当x=0.09时,由于顺磁相TiFe₂和富（R,Ti）相的析出对磁致伸缩性能不利,但相对于Tb_0.3Dy_0.7Fe_1.95母合金也有少量提高.     

CuO掺杂Ni0.4Zn0.6Fe2O4铁氧体的组织与性能探讨

采用传统球磨法制备了Ni0.4-xCu_xZn0.6Fe₂O₄（x＝0,0.12,0.20,0.28）铁氧体,并通过扫描电镜（SEM）、X-ray衍射（XRD）、综合热分析（TG-DSC）和振动样品磁强计（VSM）等手段研究掺杂CuO对Ni-Zn铁氧体的显微组织、相组成和磁性能。结果表明,随着CuO含量的增加,第二相Ni-Cu-Zn相生成,且 Ni-Cu-Zn铁氧体衍射峰强度逐渐增强;从显微组织形貌和能谱可以看出,Cu ^2＋参与了铁氧体的反应,CuO含量增加得越多,样品烧结性能越好,并促使Ni-Cu-Zn铁氧体的晶化温度降低;磁滞回线显示了Ni0.4-xCu_xZn0.6Fe₂O₄（x＝0,0.12,0.20,0.28）铁氧体的软磁特性,CuO原子分数x为0.2时的铁氧体的饱和磁化强度（Ms）最高,且具有较低的矫顽力（Hc）。     

掺杂sc的CaZrO3的制备及电学性能

采用掺杂Sc₂O₃,通过固相反应法制备了CaZr_1-xSc_xO_3-α（x=0,0.1,0.15）材料.在610-850℃采用交流阻抗谱法测定了CaZr_1-xSc_xO_3-α的电导率及电导激活能,并对CaZrO₃掺Sc及掺In样品的电学性能进行了比较.结果表明:在610-850℃,CaZrO₃的电导率为4.3×10^-19-1.4×10^-6S/cm,CaZr_1-xSc_xO_3-α（x=0.1,0.15）的电导率为1.16×10^-4-1.4×10^-3S/cm,CaZr_1-xIn_xO_3-α（x=0.1,0.15）的电导率为0.34×10^-4-4.33×10^-4S/cm,且随着温度的升高而提高;掺杂能极大提高CaZrO₃的电导率,并随着掺杂量的增加,电导激活能降低,电导率增加;温度及掺杂量相同时,掺Sc材料电导率明显高于掺In材料,说明掺Sc对提高材料的电导率更有效.     

Electrochemical hydrogen storage characteristics of La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr, Pr; x =0, 0.1) alloys prepared by melt spinning

In order to ameliorate the electrochemical hydrogen storage performances of La-Mg Ni system A2B7-type electrode alloys,the partial substitution ofM (M =Zr,Pr) for La was performed.The melt spinning technology was used to fabricate the La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr,Pr; x =0,0.1) electrode alloys.The influences of the melt spinning and substituting La with M (M =Zr,Pr) on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated.The analysis of XRD,SEM,and TEM reveals that the as-cast and spun alloys have a multiphase structure composed of two main phases (La,Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2.The as-spun (M =Pr) alloy displays an entire nanocrystalline structure,while an amorphous-like structure is detected in the as-spun (M =Zr) alloy,implying that the substitution of Zr for La facilitates the amorphous formation.The electrochemical measurements exhibit that the substitution of Pr for La clearly increases the discharge capacity of the alloys; however,the Zr substitution brings on an adverse impact.Meanwhile,the M (M =Zr,Pr) substitution significantly enhances its cycle stability.The melt spinning exerts an evident effect on the electrochemical performances of the alloys,whose discharge capacity and high rate discharge ability (HRD) first mount up and then fall with the growing spinning rate,whereas their cycle stabilities monotonously augment as the spinning rate increases.     

Effect of Mn concentration on the spin glass transition temperature of Fe0.70−xMnxAl0.30 alloys

Magnetization measurements on zero field cooled (ZFC) and field cooled (FC) samples as a function of temperature where made on Fe_0.70−xMn_xAl_0.30 alloys with 0≤x≤0.10. Our data show the existence of two regimes of the spin glass temperature T_f when increasing the concentration x of the Mn atoms. We found that T_f decreases slowly with increasing x up to x=0.06 and then shows a rapid linear decrease above this concentration. The existence of two regimes of T_f behavior with x may be attributed to the disappearance of ferromagnetic clusters which exist for low values of x (x<0.06). Compared to the Mn-free alloy, the relative changes in T_f are bigger and exceed 40% at x=0.10. The second regime (x>0.06) is associated with more influence of x on T_f.     

Structure and transformation behaviour of rapidly solidified Ni–Al–Hf alloys

Rapidly solidified Ni–Al–Hf alloys of ternary eutectic compositions were studied by X-ray diffractometry, transmission electron microscopy and differential scanning calorimetry. Ni₆₆Hf₂₀Al₁₄ amorphous alloy with relatively high Hf/Al ratio showed high tensile strength of 1600 MPa and high thermal stability against crystallization. The formation of a nanoscale metastable intermetallic compound having a body-centered cubic lattice with a lattice parameter of a=1.22 nm was observed in the alloys with higher Al than Hf content. The transformation of an amorphous+metastable cubic mixture to AlNi₃ produces AlNi₃ of the same composition as the AlNi₃ phase formed on rapid solidification. Pm m AlNi₃ phase can dissolve up to 11 at.% Hf.     

Preparation of W–Al–Mo ternary alloys by mechanical alloying

Single phase W_XAl₅₀Mo_50−X (X = 40, 30, 20 and 10) powders have been synthesized directly by mechanical alloying (MA). The structural evolutions during MA and subsequent as-milled powders by annealing at 1400 °C have been analyzed using X-ray diffraction (XRD). Different from the Mo₅₀Al₅₀ alloy, W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys were stable at 1400 °C under vacuum. The results of high-pressure sintering indicated that the microhardnesses of two compositions, namely W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys have higher values compared with W₅₀Al₅₀ alloy.     

Electrochemical properties of the MmNi3.55Mn0.4Al0.3Co0.75−xFex (x = 0.55 and 0.75) compounds

The hydrogen storage alloys MmNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x (x = 0.55 and 0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. For the MmNi_3.55Mn_0.4Al_0.3Co_0.2Fe_0.55 compound, the discharge capacity reaches its maximum of 210 mAh/g after 12 cycles and then decreases to 190 mAh/g after 30 charge–discharge cycles. However, for the MmNi_3.55Mn_0.4Al_0.3Fe_0.75 compound, the discharge capacity reaches its maximum of 200 mAh/g after 10 cycles and then decreases to 160 mAh/g after 30 cycles.

The diffusion behavior of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi_3.55Mn_0.4Al_0.3Co_0.2Fe_0.55 and MmNi_3.55Mn_0.4Al_0.3Fe_0.75 are, respectively, equal to 2.96 × 10⁻⁹ and 4.98 × 10⁻¹⁰ cm² s⁻¹. However, the values of the charge transfer coefficients are, respectively, equal to 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.     

La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-xFex合金的相结构和电化学储氢性能（英文）

采用感应熔炼和热处理的方法制备La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75?xFex(x=0~0.20)合金,并研究合金的相结构和电化学储氢性能。全部合金均为单一的具有CaCu5结构的LaNi5相,LaNi5相的晶格常数a和晶胞体积随着x值的增加而增大。最大放电容量随着x值的增加从319.0mA·h/g(x=0)降低到291.9mA·h/g(x=0.20)。在1200mA/g的电流密度下HRD值从53.1%(x=0)降低到44.2%(x=0.20)。合金电极的循环稳定性随着x值的增加而增强,这主要归因于合金抗粉化能力的增强。