Phases and thermoelectric properties of Ge1−x(Pb0.9Yb0.1)xTe alloys

A series of Ge_1−x(Pb_0.9Yb_0.1)_xTe alloys with x = 0.05, 0.10, 0.15, 0.20 and 0.30 were prepared by a conventional melting and a spark plasma sintering (SPS) techniques. The phases and thermoelectric properties for the alloys were investigated. The alloys consist of the GeTe-based rhombohedral single phase for x = 0.05, while both GeTe-based rhombohedral and PbTe-based rock-salt phases due to spinodal decomposition for the higher Pb content (x ≥ 0.10). The amount of the PbTe-based phase increases with the Pb content x increasing. All samples show p-type conduction. As Pb content x increases, the thermal conductivity reduces obviously, while the Seebeck coefficient and the electrical resistivity increases slightly. The maximum ZT of 1.4 at 723 K was eventually achieved in the sample with x = 0.15 due to its rather low thermal conductivity, from 3.7 W m⁻¹K⁻¹ at room temperature to 1.4 W m⁻¹K⁻¹ at 723 K (3.7–1.4 W m⁻¹K⁻¹), relative high Seebeck coefficient (46.5–141 μV K⁻¹) and relative low electrical resistivity (3.0–7.36 μΩ m).     

Magnetic properties and tuneable magnetocaloric effect with large temperature span in GdCd1−xRux solid solutions

The magnetic properties and the magnetocaloric effect (MCE) in the GdCd_1−xRu_x (x = 0.1, 0.15, and 0.2) solid solutions have been systematically investigated. A large reversible MCE has been observed in GdCd_1−xRu_x accompanied by a second order magnetic phase transition from paramagnetic to ferromagnetic at T_C ∼ 149, 108, and 73 K for x = 0.1, 0.15, and 0.2, respectively. Under a field change from 0 to 7 T, the maximum values of magnetic entropy change (–ΔS_M^max) are 5.6, 7.8, and 11.0 J/kg K for x = 0.1, 0.15, and 0.2, respectively, the corresponding values of the relative cooling power (RCP) are 889, 852, and 828 J/kg. The considerable reversible MCE and large RCP values together with the tuneable T_M in a wide temperature range make the GdCd_1−xRu_x solid solutions considerable for active magnetic-refrigeration.     

Influence of High-Pressure Coolant Assistance on the Machinability of the Titanium Alloy Ti555–3

The origin of this article is the quantification of productivity gains and the improvement in surface integrity seen for a recent titanium alloy that is seeing increasing use in the aeronautical industry. The Ti555–3 titanium alloy, which is starting to find greater application in the aeronautical field, exhibits certain difficulties in terms of machining. High Pressure Coolant (HPC) assisted turning consists of projecting a high pressure coolant jet between the chip and the tool. Comparisons are made between assisted turning using variable jet pressure and conventional turning (dry and classical lubrication). It is shown that it is possible to improve productivity by using HPC-assisted machining. The results highlight good chip fragmentation and a great improvement of tool life with HPC assistance. Surface integrity is also shown to be improved, through surface roughness parameters that decrease, and surface residual stresses that become more compressive. These effects have been attributed to the thermo-mechanical action of the coolant jet resulting in lower cutting forces, lower coefficient of friction and lower temperature in the cutting zone.     

基于不旋转轴肩的铝镁异种材料搅拌摩擦焊

焊具是搅拌摩擦焊的核心,对焊接质量起至关重要的作用. 利用不旋转轴肩焊接系统对6061-T6铝和AZ31B镁合金进行连接,重点分析传统和不旋转轴肩焊接系统下接头成形和力学性能等. 结果表明,与传统工艺相比,采用不旋转轴肩工艺的接头表面成形更加光滑,焊核区以典型铝镁混合的叠层结构为主,且铝镁冶金结合界面呈弯曲状,有效地增强了铝镁异种材料的机械咬合效果;焊缝区金属间化合物层明显减小,其主要是由不旋转轴肩增强焊核区材料的搅拌效果并起到“热沉”的作用所致. 采用不旋转轴肩的接头最大抗拉强度为137 MPa,较传统工艺提高了28%.     

W-Mo合金CMP工艺参数的影响与优化研究

简述了金属化学机械抛光的机理。将半导体制造工艺中的化学机械抛光技术拓展并应用到W-Mo合金表面加工中,在实现W-Mo合金材料表面高平坦度、低粗糙度的前提下,提高W-Mo合金去除速率。针对W-Mo合金的性质,选用碱性抛光液,并采用田口方法对抛光液pH值、抛光压力和抛光盘转速三个重要因素进行了优化设计,得到以去除速率为评价条件的综合最优抛光参数。实验分析表明,当抛光液pH值为11,抛光压力为80 kPa,抛光盘转速60 r/min时,可以获得较高的去除速率。     

Isothermal solid‐state transformation kinetics applied to Pd/Cu alloy membrane fabrication

In this work, time‐resolved, in situ high‐temperature X‐ray diffraction was used to study the solid‐state transformation kinetics of the formation of the fcc Pd/Cu alloy from Pd/Cu bilayers for the purpose of fabricating sulfur‐tolerant Pd/Cu membranes for H₂ separation. Thin layers of Pd and Cu (total ～15 wt % Cu) were deposited on porous stainless steel with the electroless deposition method and annealed in H₂ at 500, 550, and 600°C. The kinetics of the annealing process was successfully described by the Avrami nucleation and growth model, showing that the annealing process was diffusion controlled and one dimensional. The activation energy for the solid‐state transformation was 175 kJ/mol, which was similar to the activation energy of Pd‐Cu bulk interdiffusion. Furthermore, the Avrami model was able to successfully describe the changes in permeance and activation energy observed in Pd/Cu alloy membranes during characterization as they were annealed at high temperatures. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Atomic emission spectroelectrochemistry applied to dealloying phenomena II. Selective dissolution of iron and chromium during active-passive cycles of an austenitic stainless steel

Atomic emission spectroelectrochemistry was used to investigate selective dissolution of a 304 austenitic stainless steel sample in 2 M H₂SO₄. The partial dissolution rates of Fe, Cr, Ni, Mn, Mo, and Cu were measured as function of time during a series of potentiostatic triggered activation/passivation cycles. When first exposed to sulfuric acid solution, the steel sample was in a passive state with a total steady state ionic dissolution rate expressed as an equivalent current density of 10 μA cm⁻². A transition into the active and passive state could be triggered by cathodic (−700 mV vs. Ag/AgCl) and anodic (+400 to +700 mV vs. Ag/AgCl) potentiostatic pulses respectively of variable time. Excess Cr dissolution was observed during the activation cycle as compared to Fe and a depletion of Cr dissolution was observed during the passivation cycle. These results are interpreted in terms of the dissolution of a Cr rich passive layer during activation and selective dissolution of Fe, Mn, Ni and other elements to form a Cr rich passive layer during passivation. Quantitative analysis of the excess Cr showed that the residual film contained approximately 0.38 μg Cr/cm². Fe does not appear to be incorporated into the film at this early stage of passive film growth. Residual films of metallic nickel and copper were formed on the surface during the active period that subsequently dissolved during passivation.     

Photoelectrochemical study of nickel base alloys oxide films formed at high temperature and high pressure water

The oxide film formed on nickel base alloys at high temperature and high pressure water exhibits semi-conducting properties evidenced by photocurrent generation when exposed to monochromatic light. The use of macro- and micro-photoelectrochemical techniques (PEC and MPEC) aims to identify the different semiconductor phases and their distribution in the oxide film.Three different nickel base alloys were corroded in recirculation loop at 325 °C in pressurised water reactor primary coolant conditions for different exposition durations.PEC experiments on these materials enable to obtain macroscopic energy spectra showing three contributions. The first one, with a band gap around 2.2 eV, was attributed to the presence of nickel hydroxide and/or nickel ferrite. The second one, with a band gap around 3.5 eV, was attributed to Cr₂O₃. The last contribution, with a band gap in the range of 4.1-4.5 eV, was attributed to the spinel phase Ni_1−xFe_xCr₂O₄. In addition, macroscopic potential spectra recorded at different energies highlight n-type semi-conduction behaviours for both oxides, Cr₂O₃ and Ni_1−xFe_xCr₂O₄.Moreover, MPEC images recorded at different energies exhibit contrasted regions in photocurrent, describing the distribution of nickel hydroxide and/or nickel ferrite and Cr₂O₃ in the oxide film at a micron scale.It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in the oxide scale.     

Passive behavior of magnesium alloys (Mg-Zr) containing rare-earth elements in alkaline media

The passive behavior of magnesium alloys ZK31, EZ33 and WE54 was studied in alkaline media (NaOH - pH 13) in the presence and absence of chloride ions. The electrochemical properties were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements.X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the study of the chemical composition and surface morphology of the surface films, respectively.The electrochemical impedance results revealed that the film formed on the surface of the three alloys is characterized by an increasing resistance, which stabilized with time. In the absence of chloride the film resistance was identical for all the three alloys. However, in the presence of chloride, the resistance of the film formed on the EZ33 alloy dropped nearly one order of magnitude comparatively to the other alloys. Generally, in the presence of chloride there was a decrease of the conductive character of the film.The films are homogeneous and, according to the XPS results, the outer layer seemed mainly composed of Mg(OH)₂ and the internal layer composed of MgO, independently of the presence of chloride. The AFM study revealed that the presence of chloride affected film morphology, namely nano-crystallites dimensions and aggregates size that increased.     

锌镍合金镀层的耐蚀性能研究

在低碳钢表面电镀锌镍合金薄膜.考查了pH值、电流密度和镀液温度等因素对镀层质量的影响.采用XRD与SEM研究镀层的结构和形貌.选择3.5%NaCl溶液作为腐蚀介质,用稳态法研究了镀层的耐蚀性能,得出了较有价值的结论.