Heavy rare earth based bulk metallic glasses with high thermal stability

We report a family of ternary Gd–Al–Co alloys based on the heavy gadolinium rare earth element can be readily cast into fully glassy rod by a conventional casting method. It is found that the bulk metallic glasses (BMGs) have much high thermal stability (i.e. high glass transition temperature and crystallization temperature) and high moduli compared with those of other known rare-earth based BMGs. It is confirmed that, in addition to the strong chemical interaction among the components, the high bulk modulus of the base component in the BMGs is dominantly responsible for the high thermal stability. The thermal stability is correlated with the bulk modulus of the base element in the rare earth based BMGs.     

Soft magnetic properties of carbide-dispersed nanocrystalline films with high thermal stability

Nanocrystalline Fe-M-C, Co-M-C, and Ni-M-C (M = group IVa-VIa metals) films in which extremely fine M-carbide particles are dispersed were prepared by annealing sputter-deposited amorphous alloy films. Of these films, the Fe-M-C and Co-M-C films exhibited good soft magnetic properties. These soft magnetic properties were maintained after annealing at elevated temperatures, because carbide particles dispersed in the films considerably retard the grain growth of Fe-rich or Co-rich nanocrystallites. Films containing Ta or Hf exhibit particularly high thermal stability (around 1000 K). On the other hand, Zr and Hf are suitable for obtaining high saturation magnetization,Is, because the amount of these elements needed for amorphization is less than other M elements. The highest Is of films containing Zr or Hf was 1.7 T for Fe-M-C and 1.6 T for Co-M-C films. Because the magnetostriction of Fe-M-C films is dominated primarily by the C concentration dissolved into Fe, zero-magnetostrictive films can easily be attained by controlling the C to M ratio or annealing conditions. In addition to the good performance of Fe-Hf-C films, a higherIs value of 2.0 T was achieved by multilayering the Fe-Hf-C with Fe, and improved frequency characteristics of permeability as well as higher thermal stability by about 100 K was achieved by Si additions without sacrificing other properties. These carbide-dispersed nanocrystalline films are suitable for use in high-density magnetic recording heads fabricated by glass bonding processes.     

Toward a high specific power and high stability polypyrrole supercapacitors

Polypyrrole (PPy) films doped by p-toluenesulfonic (PTS) are prepared by pulse current polymerization (PCP PPy) in aqueous solutions. Cations (H⁺, Li⁺, Na⁺, and K⁺ ions) in working electrolyte solutions have a great influence on the electrochemical properties of PCP PPy films for supercapacitors. In 3 M aqueous chloride solutions, the smaller cations lead to the better electrochemical properties of PCP PPy films. PCP PPy films show ideally capacitive characteristics with a very high specific power of 110.9 kW kg^?1 in 3 M HCl when its specific energy reaches 18.4 Wh kg^?1. PCP PPy films are very stable in 3 M HCl, showing less than 4% decay over 160,000 and 20,000 charge/discharge cycles at current density of 40 A g^?1 within voltage range of 0–0.4 V and 0–0.8 V, respectively. The results of SEM show that many pits and grooves appear on the surface of PPy anode in 3 M KCl after 30,000 cycles, which should be main reason of rapid decay of PPy capacitance in 3 M KCl.     

低温球磨制备高热稳定性纳米晶Al-Zn-Mg-Cu合金块体材料

利用液氮球磨和真空热压技术制备纳米晶Al-10Zn-3Mg-1.8Cu(质量分数,%)合金块体材料。采用X射线衍射(XRD)和透射电镜(TEM)对材料在制备过程中的固态相变、晶粒尺寸和热稳定性进行分析。结果表明,材料经过液氮球磨15 h后晶粒尺寸为37 nm,真空热压后材料晶粒保持在100 nm,热挤压后晶粒尺寸约为300 nm,热处理后晶粒尺寸保持不变。材料的高热稳定性原因在于大量合金元素和杂质元素超饱和固溶于Al基体中阻止了晶粒的长大,以及细小析出MgZn2相和Al2O3颗粒对于晶界的钉扎作用。     

The effect of low-temperature conditions on the electrochemical polymerization of polypyrrole films with high density,high electrical conductivity and high stability

High-quality polypyrrole-hexafluorophosphate (PPy-PF₆) films with high density (∼1.4 g/cm³), high conductivity (>300 S/cm for unstretched film) and high electrochemical stability are obtained reproducibly by galvanostatic polymerization at low-temperature conditions. The optimal polymerization current density of J_p=0.02–0.05 mA/cm² was obtained at the polymerization temperature of T_p=−40°C. The surface morphology of the film sensitively varies depending upon the properties of electrode and its surface conditions. The transport measurements characterize the high-density PPy-PF₆ film as a disordered metal close to the boundary of disorder induced metal–insulator (M–I) transition. The X-ray diffraction measurements suggest that partially crystalline structure of PPy-PF₆ film is related to the transport properties. The uniaxial stretching induces an increase of the conductivity up to ∼930 S/cm in a direction parallel to stretching as well as the anisotropy of conductivity. The comparative studies of thermogravimetric analysis (TGA), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for PPy-PF₆ films prepared at room-temperature and low-temperature conditions show that the latter exhibit better thermal stability as well as electrochemical stability under long oxidative polarization.     

A Dy-based bulk metallic glass with high thermal stability and excellent magnetocaloric properties

A new heavy rare-earth-based Dy₃₆Ho₂₀Al₂₄Co₂₀ bulk metallic glass (BMG) with high thermal stability and excellent magnetocaloric properties has been prepared by a copper mold casting. Compared with the other known rare-earth-based BMGs, this BMG alloy possess higher glass transition temperature and crystallization temperature, larger effective activation energy for glass transition and crystallization. Under a modest magnetic field, this BMG alloy exhibits a comparable or even larger magnetocaloric effect than that the previously reported RE-based BMGs and crystalline compounds. The high thermal stability and the excellent magnetocaloric effect together with other merits of the BMGs make this BMG alloy suitable candidate for use as magnetic refrigerant in a temperature range below 50 K.     

高稳定高效率十八辊轧机的开发与应用

针对十八辊型轧机在实际生产中普遍存在的侧支撑系统稳定性差、背衬轴承消耗大、工作辊断裂、止推轴承损坏频繁等诸多问题,对十八辊轧机侧支撑系统的稳定性、工作辊和止推轴承的故障原因及影响轧机效率的原因进行了研究分析,提出相应解决措施,开发出新型侧支撑辊盒锁紧机构、侧支撑标定装置以及快速换辊装置等多项专有技术,最终获得了一种故障率大幅度降低的高稳定性、高效率的十八辊轧机,并在中冶南方印度不锈钢项目上得到良好应用。     

高温合金旋压塑性变形稳定性试验研究

通过高温合金管材不同旋压变薄率的试验，探讨了常用高温合金的旋压工艺参数。在高温合金管材可旋性试验的基础上，有效控制塑性变形的稳定流动，可以旋压高精度薄壁管材。当坯料退火以后，经旋压工艺参数优化，可提高变形区金属三向塑性流动的稳定性，并有助于获取尺寸精良的管材。     

Synthesis of magnetic carrier sub-microparticles with high stability through carbon reduction and solation coating methods

This paper presents a novel approach in synthesizing SiO_2–Fe_3O_4magnetic carrier with high stability.The Fe_3O_4 magnetic powders were synthesized via onestep method named carbon reduction method. The advantages of the methods are of simple process, none lead-in pollution agent, low cost and adaptation to large-lot production. The stability of the magnetic powders is improved through modifying the Fe_3O_4 with SiO_2 in solation method.The results of the characterizations show that the superparamagnetic SiO_2–Fe_3O_4sub-microparticles(~600 nm)with saturation intensity of 36.4 m A·m~2·g~(-1)are obtained successfully. Moreover, the quantitating, repeatability and high stability of the carbon reduction method are demonstrated as well.     

变齿距铣刀高速微铣削的动态特性及稳定性研究

在高速微铣削加工过程中,提高生产效率和零件质量的需求日益强烈,这使得机床一直在系统的动态稳定性极限附近工作,而机床颤振的存在是限制微铣削加工生产率的主要障碍.基于颤振稳定性的准确预测,能采取一些措施来提高动态稳定性极限,例如通过改变铣刀结构.提出了数值分析与铣削实验相结合的方法,采用变齿距微铣刀来研究铣削加工的动态特性和稳定性.另外提出了采用时域仿真的输出力来表征加工稳定性的新方法,采用变齿距铣刀可以非常有效地提高某些速度范围的颤振稳定性.对于选定刀具的加工,这种方法可以用于加工优化,或在设计阶段预测刀具新型结构的性能.     

Synthesis and nonlinear optical properties of novel polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)-4′-nitrostilbene (2) was prepared and condensed with 2,4-toluenediisocyanate (TDI), 3,3′-dimethoxy-4,4′-biphenylenediisocyanate and 1,6-hexamethylenediisocyanate to yield polyurethanes (3–5) containing the nonlinear optical (NLO)-chromophores 2,3-dioxynitrostilbenyl groups, which constitute parts of the polymer backbones. The resulting polymers (3–5) were soluble in common organic solvents such as acetone and N,N-dimethylformamide (DMF). These polymers showed a thermal stability up to 260 °C in thermogravimetric analysis (TGA) thermograms with glass transition temperature (T_g) values in the range 100–155 °C in differential scanning calorimetry (DSC) thermograms. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films were around 5.48×10⁻¹⁰ esu. These poled polymers exhibited a greater thermal stability of dipole alignment even at 20 °C higher than T_g due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications.     

Turning machining induced microstructural stability of a high Nb-containing TiAl alloy during high temperature exposure

Turning machining induced microstructural instability was investigated in a fully lamellar Ti-45Al-8.5Nb-(W,B,Y) alloy during high temperature exposure.After turning machining followed by thermal exposure at900 or 1000℃ for 100,300 and 500 h,a depth-dependent gradient microstructure with random orientations was produced in the region close to the machining surface.Two typical layers,a fine-grained(FG) layer with equiaxed grains and a coarse-grained(CG) layer with elongated grains,are formed in this region in transversal direction.The thickness of the two layers is up to 120 urn after thermal exposure at 1000℃ for 500 h,which is less than the depth of the hardened region(200 μm) after turning machining.Most of the new grains in FG and CG layers are constituted of γ single phase,while short α_2 segments and few B2 particles are precipitated at the γ/γ interface or inside the γ grains.Recrystallization and phase boundary bulging are found to be the major mechanisms responsible for lamellar degradation in FG layer and CG layer,respectively.The residual deformation energy stored is considered to be the main driving force of this process.