Farhad GHARAVI
,
Khamirul A MATORI
,
Robiah YUNUS
,
Norinsan K. OTHMAN
,
Firouz FADAEIFARD
中国有色金属学报(英文版)
doi:10.1016/S1003-6326(16)64159-6
采用氯化钠+过氧化氢溶液浸泡试验研究AA6061-T6铝合金搅拌摩擦焊搭接接头的腐蚀行为。采用循环动电位极化测试、扫描电子显微镜和能谱仪表征腐蚀形貌，揭示焊接区与基体合金的腐蚀机理。研究了焊接接头的显微组织和剪切强度。结果表明，与基体合金相比，焊接区在腐蚀溶液中会发生晶间腐蚀和点蚀。搭接剪切测试结果表明，所得焊接接头的拉伸剪切强度为128 MPa,超过基体合金强度的60%。电化学测试结果表明，焊核区和热影响区的保护电位比点蚀电位更负，说明焊核区与热影响区点蚀的趋势不强。基体合金抗腐蚀性比焊缝区的强，而热影响区的抗腐蚀性最差。点蚀主要源于金属间化合物边缘，因为与铝基体相比，金属间化合物的自腐蚀电位更高而成为阴极。由于焊缝区的金属间化合物增加，腐蚀电偶增加，焊缝的抗腐蚀性降低。
关键词:
搅拌摩擦焊
,
搭接接头
,
AA6061合金
,
点蚀
,
焊接过程
,
金属间化合物
Journal of Physics D-Applied Physics
A large magnetoresistance (MR) is observed in a double helical CoMnSi compound over the entire temperature region from 5 K to the maximum measuring temperature of 380 K, with the largest MR ratio of -18.3% at 245 K and the smallest MR ratio of -5.5% at 85 K at 5 T. This phenomenon is ascribed to two different mechanisms in different temperature regions. The suppressed spin fluctuations of the double helical structure are responsible for the MR below 110 K. However, in consideration of the natural multilayer superstructure of CoMnSi, the larger MR above 110 K is ascribed to the decrease in K-space restrictions when the change in magnetic structure from double helical order to fan order occurs.
关键词:
giant magnetoresistance;magnetic-structure;crystal;metals
Journal of Physical Chemistry C
alpha-K(x)MnO(2) nanotubes with x = 0.10, 0.12, 0.15, and 0.17 have been synthesized through acid and alkali treatments of the precursor alpha-MnO(2) nanotubes. For the samples with x = 0.10 and 0.12, a large divergence of the ZFC and FC susceptibilities and pronounced hysteresis at low temperature are observed. However, the samples with x = 0.15 and 0.17 are antiferromagnetic with Neel temperatures of 25.4 and 25.3 K, respectively. The reciprocal susceptibility and electrical conductivity indicate that the samples with x = 0.15 and 0.17 undergo a charge separation transition from mixed/averaged valence state manganese ions to Mn(3+) and Mn(4+) between 250 and 300 K. Below half occupancy of the K(+) site (x <= 0.125), the strong geometrical frustration due to the triangular lattice configuration and the mixture of Mn(3+)/Mn(4+) result in the spin-glass behavior of the samples with x = 0.10 and 0.12. Above half occupancy of the K(+) site, the samples with x = 0.15 and 0.17 exhibit an antiferromagnetic feature due to the charge separation of Mn(3+) and Mn(4+). Our experiments display that the magnetic properties of alpha-K(x)MnO(2) can be tuned by varying the K(+) content.
关键词:
hydrothermal synthesis;manganese-dioxide;hollow urchins;tunnel;phase;transitions;nanowires;growth;oxides
李丽荣
,
赵娟
,
王贵
金属功能材料
采用非晶态多核配合的方法在800℃制备出La0.85K0.15MnO3纳米颗粒,用XRD、HRTEM和PPMS等手段对纳米颗粒的微观结构和磁性能进行研究.XRD和ED分析表明,所有样品都具有单相钙钛矿结构;样品的M-丁曲线研究结果表明,La0.85K0.15MnO3纳米颗粒的居里温度Tc为242.65 K.
关键词:
居里温度
,
纳米颗粒
,
La0.85K0.15MnO3
Oxidation of Metals
The corrosion of four Fe-Cr commercial steels with different tents in a simulated waste-gasification atmosphere containing 0.5 vol.% H-2, 0.5 vol.% HCl, balance CO2 has been investigated at 773 and 873 K. The same materials have also been tested in the same gas mixture free from HCl at both temperatures for comparison. The results show that the materials with low-chromium content (2.25 CrMoV and NF616) undergo accelerated corrosion in the presence of HCl, while the stainless steel SS304 suffers very little corrosion. On the contrary a steel containing 12 wt.% Cr (12 CrMoV) corrodes rather rapidly at 773 K but quite slowly at 873 K. The beneficial effect of chromium on the corrosion resistance of the steels increases with the chromium content at both temperatures. The steels tested show corrosion rates generally decreasing with time, having kinetics which are approximately parabolic at 773 K but intermediate between parabolic and linear at 873 K Only little or even no chlorine can be detected at the scale/metal interface at both temperatures for all materials corroded in HO-containing atmospheres. The corrosion mechanism can be explained by the so-called "active-oxidation, model.
关键词:
Cr steels HCl;reducing atmosphere;corrosion;high-temperature corrosion;fe-cr alloys;hydrogen-chloride;chromium-alloys;gas-mixtures;oxygen;800-degrees-c;oxidation;metals;fuels
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
Nanoscale Research Letters
The linear thermal expansions (LTE) of bulk nanocrystalline ingot iron (BNII) at six directions on rolling plane and conventional polycrystalline ingot iron (CPII) at one direction were measured from liquid nitrogen temperature to 300 K. Although the volume fraction of grain boundary and residual strain of BNII are larger than those of CPII, LTE of BNII at the six measurement directions were less than those of CPII. This phenomenon could be explained with Morse potential function and the crystalline structure of metals. Our LTE results ruled out that the grain boundary and residual strain of BNII did much contribution to its thermal expansion. The higher interaction potential energy of atoms, the less partial derivative of interaction potential energy with respect to temperature T and the porosity free at the grain boundary of BNII resulted in less LTE in comparison with CPII from liquid nitrogen temperature to 300 K. The higher LTE of many bulk nanocrystalline materials resulted from the porosity at their grain boundaries. However, many authors attributed the higher LTE of many nanocrystalline metal materials to their higher volume fraction of grain boundaries.
关键词:
Linear thermal expansion;Bulk nanocrystallined materials;Severe;rolling technique;electrochemical corrosion behavior;different grain sizes;microstructure;diffraction;selenium;metals
荀玉强
,
杨鲁伟
,
蔡京辉
,
梁惊涛
,
周远
工程热物理学报
介绍了一套实用型单级高频同轴脉冲制冷机工作在深低温区的性能特性.输入功率为200 W时,冷头无负荷最低温度可达到29.35 K,输入功率为235 W时,冷头无负荷温度可稳定在28.55 K.这是目前国内无多路旁通的单级高频脉冲管制冷机获得的最低温度,国际上位于先进行列.200 W输入条件下,35.6 K可提供0.5 W制冷量,为30～40K温区相关的小冷量应用提供了一种简单有效的方法.
关键词:
脉冲管制冷机
,
高频
,
单级
,
同轴
,
双向
Ying LI
材料科学技术（英文）
Oxide materials NaCo2O4 and (Na1-yMy)1.6Co2O4 (M=K, 0.05≤y≤0.35; M=Ca, Sr, 0.10≤y≤0.40) were prepared by a sol-gel method. Experimental results indicated that the Seebeck coefficient and the Power-factor of Na Co2O4 were improved by doping Ca and Sr but not by K. The Power-factor of NaCo2O4 is in its maximum, 1.68×10-4 W•m-1•K-2 and 11% bigger than that of the original one when the dopant fraction of Ca was 0.1. Doping Sr makes NaCo2O4 have the biggest Power-factor, 1.68×10-4 W•m-1•K-2 that is 50% bigger than the non-doping oxide. The experimental results indicate that suitable dopants and addition amounts could improve the thermoelectric properties of NaCo2O4 greatly.
关键词:
Thermoelectric materials
,
materials
,
Electric
,
proper
