Studying the formation process of chromate conversion coatings on aluminium using continuous electrochemical noise resistance measurements

A unique electrochemical technique, namely continuous noise resistance calculation (CNRC), was used to obtain electrochemical kinetic information from the formation process of chromate conversion coatings (CCC) on aluminium electrodes. It was found that the noise resistance (R_n) of aluminium electrodes remained almost unchanged during electrodes' immersion in a chromate containing acidic solution where the CCC films were supposed to form rapidly. This result indicates that the formation of CCC was associated with continuous corrosion of the aluminium electrodes and that the CCC films formed on aluminium surface were not intact barrier films, but most likely porous layers. The CCCs became protective only after they were aged in the environment. Based on these findings, the formation and inhibition mechanisms of CCC have been discussed.     

Improved corrosion protection of aluminum alloys by electrodeposited silanes

Organofunctional silanes recently have emerged as outstanding, environmentally friendly corrosion protectors for metal substrates, compared with conventional chromate treatments. A simple immersion technique is typically used to coat the metal surface with silane films. However, the thickness and uniformity of the films are uncontrolled in this process. This paper proposes a new deposition technique for the silane films on the metal surface, i.e., by electrodeposition. Hydrolyzed silanes are water-soluble, ionized molecules, so they can be deposited on metals by electrodeposition. Various combinations of silane mixtures were tested at different voltages, pH values, bath concentrations, and exposure times on panels of alloy aluminum and mirror-polished ferro-plate. The surface structure was characterized by scanning electron microscopy (SEM) and ellipsometry. The resistance of the film to corrosion was investigated by direct current (DC) polarization and electrochemical impedance spectroscopy (EIS) techniques. Electrodeposition results in a more organized and uniform film with fewer pores, compared with immersed or dipped films. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appears on pp. 320–26 of the Proceedings.     

高锰钢的泡沫陶瓷过滤净化

采用泡沫陶瓷过滤片对高锰钢进行过滤处理，对其进行金相分析和测试密度，冲击韧性和耐磨性能，并与未过滤的高锰钢进行对比，实验结果表明，在过滤的高锰钢中，金属夹杂物明显减小，密度提高0．53％，冲击韧性39．5％，耐磨性能提高1．04倍，批量生产结果表明，过滤的高锰钢球磨机衬板的使用寿命提高0．6－0．7倍。     

用颗粒冲击磨损试验评价热喷涂陶瓷涂层的粒子间结合

热喷涂层中扁平粒子间的结合决定涂层的性能。能评价粒子间结合的简单可靠的方法对于涂层的实际应用具有十分重要的意义。然而采用传统的试验方法如拉伸试验难以获得令人满意的结果。可以预料具有去结合机理的一层接一层去除粒子的试验方法将是有效的。实验证明通过控制测试条件，颗粒冲击磨损试验能够通过去结合机理有效地使涂层产生磨损。本论文提出了陶瓷涂层颗粒冲击磨损的模型，基于涂层受颗粒冲击磨损是因一层层的粒子通过去结合而产生的机理，建立了磨损速度与粒子间结合率的关系。定义为ACT－JP值（磨损速度的倒数）的特征值与粒子间结合率的实验相关性证明了粒子间结合对陶瓷涂层磨损的控制作用和利用颗粒冲击磨损试验评价粒子间结合的可行性。     

High-Temperature Corrosion Resistance of Al–Re and Re Coatings

The oxidation behavior in air at 1473 K, and sulfidation behavior in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K of Al–Re coated CMSX-4 were studied. Investigation on the sulfidation behavior of the Re-coated CMSX-4 was carried out in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K. The experimental results show that a Re-rich alloy layer was formed between an -Al₂O₃ layer and the inner concentration zone of Ta and Ti for the CMSX-4 single crystal alloy with an Al–Re coating after oxidation. The Re-rich alloy layer containing Cr, W, Ni, Co, and Mo effectively inhibited the outward diffusion of alloying elements and the inward diffusion of Al. The Al/Re-coated CMSX-4 single crystal alloy had excellent sulfidation resistance; the Re-rich alloy layer, containing W, Ti, Ta, and Mo, which formed during the sulfidation process and located between the alumina scale and the CMSX-4 base alloy, plays a role in inhibiting the outward diffusion of alloying elements. The sulfidation resistance of CMSX-4 single-crystal alloy is greatly improved by a Re coating on the CMSX-4 alloy surface; this is attributed to a Re–Cr–W alloy layer that retarded the outward diffusion of cations and the oxide layer containing Ta, Ti, and Al, which inhibited the inward penetration of sulfur.     

熔模铸造型壳抗弯弹性模量的研究

依据材料力学、陶瓷材料的有关理论和方法,分别对水玻璃型壳、硅溶胶型壳及其复合型壳在不同温度时的抗弯弹性模量进行了测试研究.结果表明,耐火材料、温度对型壳的弹性模量有较大的影响,硅溶胶型壳和复合型壳的弹性模量值比水玻璃型壳的大.     

Effect of Si addition to CrN coatings on the corrosion resistance of CrN/stainless steel coating/substrate system in a deaerated 3.5 wt.% NaCl solution

CrSiN coatings with different Si concentration (Si/(Cr + Si) ratio: 0, 3.7, 11.7, 20%) were deposited on stainless steel substrates using a closed field unbalanced magnetron sputtering (CFUBM) system. The variation in the microstructure of the films with the Si concentration was measured by XRD. The corrosion behavior of the CrSiN coatings in a deaerated 3.5% NaCl solution was investigated by potentiodynamic tests, electrochemical impedance spectroscopy (EIS) and surface analyses. The microstructure of the CrSiN film was found to depend on the Si concentration. The results of the potentiodynamic polarization tests showed that the corrosion current density and porosity decreased with increasing Si/(Cr + Si) ratio. The EIS measurements showed that the corrosion resistance of the Si-bearing CrN was improved by the phase transformation of the film, which led to an increase in the pore resistance and charge transfer resistance. The Si-bearing CrN possesses the best corrosion resistance at a Si/(Cr + Si) ratio of 20%, measured by the maximization of the pore resistance and charge transfer resistance.     

SEBF/SLF系列重防腐涂料的特性和分析

本文介绍2种SEBF熔融结合环氧粉末涂料和2种SLF双组份液体涂料,辽宁的物理和化学性能及部分测试和评价方法.     

The application of thermal sprayed coatings for pig iron ingot molds

Molds made of gray cast iron for casting pig iron ingots are subjected to severe temperature fluctuations. The main life- limiting factor for mold damage is the formation of surface cracks arising from thermal fa-tigue. Various flame and plasma sprayed coatings were investigated to extend the life of these molds. Coating materials studied include plasma sprayed ceramic coatings with bond coats as well as flame sprayed oxidation- resistant alloy powders. The results of cyclic furnace tests from room temperature to 1100 °C in air, simulating the thermal cycle in casting, indicated that failure occurred along the interface between the bond coat and the gray iron substrate because of iron oxidation, and not at the interface between the ceramic top coat-ing and the bond coating for a superalloy substrate. The field test results indicated that plasma sprayed alumina coatings with 200 μm top coating thickness are the most promising materials for pig iron casting.     

High-temperature oxidation of aluminum electroplated Fe-Mn alloys

Austenitic Mn-Al alloys (20–32 W/O Mn, 7–10 Al, 2–3 Si, 1C) were found to have satisfactory oxidation resistance up to 950°C under isothermal conditions in air. Surface enrichment of aluminum is a necessary condition for obtaining an almost pure alumina scale for uses at higher temperatures. Four different Mn-steels were Al-coated by the Capuano electroplating process. In all the steels there was an increase in the hot-oxidation resistance. The best results were obtained with steels containing both Al and Si, and this for temperatures up to 1100°C. No spalling was noticed during rapid cooling of the test pieces. Silicon was found to act as a diffusion barrier to outward iron diffusion. It appears that there is formation of a pure, thin film of alumina from the matrix which interacts with the aluminum diffusing from the superimposed, coating for the formation of good bonds.