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991.
Dilute copper-aluminium alloys were oxidized in air from 700 to 1000 °C. Two distinctive behaviours were observed: alloys with at least 3 wt% aluminium showed excellent oxidation resistance in the whole temperature range. Alloys with 2 wt% or less aluminium exhibited good oxidation resistance up to 800 °C; but as the temperature was further increased, the oxidation rate of these alloys increased and became comparable to that of pure copper. A kinetic model was developed to explain the oxidation behaviour and indirectly determine the amount of dissolved oxygen in the alloys tested. It was found that the oxygen dissolved in alloys with up to 2 wt% Al exceeded its solubility limit in copper, whereas the dissolved oxygen in alloys with higher aluminium contents was below the solubility limit. This difference may account for the significantly different oxidation resistance. 相似文献
992.
Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion. 相似文献
993.
The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem® (7?pH?13). XPS results showed that the corrosion products developed in both media consisted of Fe2O3, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11?pH?13, the steel is covered by a passive film, while for pH?10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated. 相似文献
994.
[FePt/C]n多层膜的结构和磁学性能 总被引:1,自引:1,他引:1
采用磁控溅射方法制备FePt(50nm)和[FePt(2nm,3nm,5nm)/C(1nm)]。膜,并在550℃退火30min,研究了周期数(n)对FePt/C系列多层膜结构及磁学性能的影响。结果表明:退火后多层膜的矫顽力在总膜层厚度约为30nm时出现最大值;随着n的增大,多层膜的饱和磁化强度和晶粒尺寸均不断增大;C的加入可以有效降低晶粒间交换耦合作用。刚此可以通过控制周期数得到县仃合适的微观结构和高的磁学性能的FePt/C多层膜,从而满足超高密度磁记录介质的要求。 相似文献
995.
硬质合金与钢的热等静压扩散连接 总被引:2,自引:1,他引:2
研究了硬质合金YG15C与45~#碳钢的热等静压扩散连接工艺,探讨厂连接温度、压力、保温保压时间、中间夹层及其厚度和连接残余热应力等对接合强度的影响.结果表明:热等静压扩散连接强度强烈依赖于连接温度,受控于连接后因YG15C与45~#钢热膨胀失配而产生的残余热应力。采用镍箔作中间夹层可有效地减小残余热应力对连接的影响,显著提高接合强度. 相似文献
996.
A coating consisting of (Cr2N−Mo2S3) overlay coating and an underlying Cr coating was deposited on a steel substrate by D.C. magnetron sputtering. The oxidation
characteristics of the deposited double-layered coating were studied at temperatures ranging from 400 to 900 °C in air. The
oxidation product was primarily Cr2O3. The unreacted coating beneath the oxide scale had some dissolved oxygen, sulfur, and iron. Oxidation of the coating occurred
via complex routes such as the outward diffusion of chromium and nitrogen from Cr2N and iron from the substrate, and the inward transport of oxygen from air, chromium from Cr2N, and S from Mo2S3. This counter diffusion of various ions occurred easily via fine crystallites that constituted the coating, which had some
solubility of S, O, and Fe. 相似文献
997.
Effects of coating thickness and residual stresses on the bond strength of ASTM C633-79 thermal spray coating test specimens 总被引:1,自引:0,他引:1
D. J. Greving J. R. Shadley E. F. Rybicki D. J. Greving J. R. Shadley E. F. Rybicki 《Journal of Thermal Spray Technology》1994,3(4):371-378
Wire-arc-sprayed nickel-aluminum is widely used in the aircraft industry for dimensional restoration of worn parts and as
a bond coat for thermal barrier coatings and other top coats. Some repair applications require thick coatings, which often
result in lower bond strength. A mechanism being investigated to ex-plain this decrease in bond strength is the free edge
effect, which includes both coating residual stresses and coating thickness. The layer-removal method was used to determine
experimentally the residual stresses in wire-arc-sprayed nickel-aluminum coatings of different thicknesses. Bond strength
evalu-ations were performed using an improved ASTM C 633-79 test specimen. Finite-element analysis and fracture mechanics
were used to investigate the effects of coating thickness and residual stress state on coating bond strength. 相似文献
998.
999.
The extended X-ray absorption fine structure (EXAFS) method and transmission electron microscopy (TEM) have been used for characterizing the local structure and morphology of ferric oxyhydroxides, α-FeOOH and γ-FeOOH, with and without chromium. These ferric oxyhydroxide powders were prepared from aqueous solutions containing iron and chromium ions. Radial structural functions for iron obtained by Fe K edge EXAFS spectra showed that the linkage of structural units formed by FeO6 octahedra in γ-FeOOH is distorted by chromium addition, while such distortion in α-FeOOH is not clearly detected. On the other hand, Cr K edge EXAFS spectra showed that the local structure around chromium does not necessarily correspond to the local structure around of iron, which is observed by Fe K edge EXAFS spectra. This suggests that the structural units containing iron and chromium are heterogeneously distributed in these ferric oxyhydroxides. The local structural information was discussed coupled with morphological features of these ferric oxyhydroxides observed by TEM. 相似文献
1000.
The effect of corrosion inhibiting pigments on environmentally assisted cracking of high strength aluminum alloy 总被引:2,自引:0,他引:2
The effects of some corrosion inhibiting pigments on environmentally assisted cracking of 7075-T76 aluminum alloy were examined in 3.5% NaCl (pH=6.2) solution. In order to study the inhibition mechanism of these pigments in environmentally assisted cracking of aluminum alloy, electrochemical polarization tests were carried out in 3.5% NaCl (pH=6.2 and 3) and 0.1 M HCl solutions respectively with the presence and absence of these pigments. The results showed that the effects of the pigments on environmentally assisted cracking of aluminum alloy were exhibited mainly at crack initiation and the early stage of crack propagation. A nontoxic compound, composed of phosphate, molybdate, citrate, and thiazole/imidazole derivatives, was a promising pigment to inhibit environmentally assisted cracking of the alloy. 相似文献