Effect of Al content on high temperature erosion properties of arc-sprayed FeMnCrAl/Cr_3C_2 coatings

Three types of FeMnCrAl/Cr3C2 coatings with different Al content were deposited on 20# steel substrates by the high velocity arc spraying (HVAS) process. Surface microstructures of the coatings were analyzed by optical microscopy (OM) and X-ray diffractometry (XRD). High temperature erosion (HTE) tests were performed in an erosion tester at different impact angles. The surface morphologies of the eroded coatings were observed on a field emission scanning electron microscope(FE-SEM). The laminated structure is found on all the prepared coatings with the porosity and oxide fraction in the coatings decreasing with the Al content from 0 to 15% (mass fraction). Sample FA3 with 15% Al, possessing the lowest porosity and oxide fraction, has the best HTE resistance, which demonstrates that Al addition can improve the HTE resistance of the coatings. The erosion rate of sample FA1 exhibits a maximum value at 90° impact angle. The maximum erosion rates of both FA2 and FA3 samples appear in the range of 60°-90° impact angles. Erosion loss of the coatings occurs through brittle breaking, cutting and fatigue spalling.     

粉末粒度对碳/碳基体上羟基磷灰石涂层的影响

采用等离子喷涂技术在碳纤维增强碳复合材料(简称碳／碳复合材料)上制备了羟基磷灰石涂层,研究了原始粉末粒度对涂层的表面形貌、剪切强度、相组成等方面的影响,并分析了涂层与基体的界面结合状况。结果表明：采用粗粉末喷涂后得到的涂层结合强度较高．结晶程度也较高,但涂层与基体的结合机制仍为机械嵌合。     

Magnetic field-assisted finishing for micropore X-ray focusing mirrors fabricated by deep reactive ion etching

A magnetic field-assisted finishing process has been studied for high-aspect-ratio ion-etched silicon curvilinear micropore structures, which have potential application as mirrors for satellite-borne X-ray telescopes. The micropore sidewalls act as X-ray focusing mirrors, and lead to reductions in the mass-to-effective-area ratio of 10-1000 times, compared to traditional X-ray telescopes. This paper describes the processing principle for the surface finishing of the sidewalls of micropore structures (10, 20 μm and depth: 300 μm (aspect ratio ≈ 15, 30)), and the feasibility of achieving roughness ∼4 nm rms and improving the X-ray reflectivity of micropore sidewall surface are demonstrated.     

Microstructural Evolution of Alumina Layers on an Al–Cu–Fe Quasicrystal during High-Temperature Oxidation

The oxidation of a quasicrystal with the nominal compositionAl₆₃Cu₂₅Fe₁₂ was studied around 800°Cin environmental and synthetic air by means of thermogravimetric analysis,electron microscopy, and analytical electron spectroscopy. In an earlyoxidation stage, -Al₂O₃ formed with an orientational relationship tothe quasicrystal. At the oxide–metal interface, -Al₂O₃transformed into large hexagonal shaped -Al₂O₃grains. The change in surface morphology indicated that at theoxide–gas interface -Al₂O₃ continued togrow as -Al₂O₃. Locally the metastable aluminalayer was transformed thoroughly into -Al₂O₃,which then continued to grow with a nodular morphology. On top of the oxidenodules, several at.% of Cu²⁺ were detected.     

The Effect of Inorganic Pollutants on the Biocorrosivity of Marine Environment to a Low-Carbon Steel

The effect of heavy metals such as Fe, Zn, Pb, Cd, and Cu in quantities simulating economical pollution of natural sea water on its biological pollution and corrosivity to a low-carbon CT3 steel is investigated under laboratory conditions. It is shown that under the experimental conditions, the steel corrosion is controlled by biological factor of the medium. __________ Translated from Zashchita Metallov, Vol. 41, No. 6, 2005, pp. 614–619. Original Russian Text Copyright ? 2005 by Suponina, Koryakova, Kharchenko.     

A TEM investigation of the <Emphasis Type="Italic">γ/γ′</Emphasis> phase boundary in Pt-based superalloys

Precipitation-strengthened alloys in the system Pt-Al-Cr-Ni have been investigated by transmission-electron microscopy. Dense dislocation networks were found in an alloy with the nominal composition, in atomic percent, Pt-14Al-3Cr-4Ni after homogenization heat treatment and aging. Alloys with higher nickel content showed low overall dislocation densities and the γ/γ′ phase boundaries were almost free of dislocations. The loss of coherency in the alloy with a low nickel content is explained by high lattice misfit. For more information, contact Stefan Vorberg, University of Applied Sciences Jena, Department of Materials Technology, Carl-Zeiss-Promenade 2, Jena D-07745, Germany; +49-3641-205-466; fax +49-3641-205-451; e-mail stefan.vorberg@fh-jena.de.     

阳离子对P110钢高温高压CO2腐蚀反应过程的影响

运用腐蚀失重、腐蚀表面成分分析和电化学测量技术，研究了在高温高压条件下阳离子对P110油管钢CO2腐蚀行为的影响.结果表明：随着试验时间的延长，阳离子的存在使得电极反应速率降低较慢，它不仅通过在金属表面成膜影响腐蚀反应的阳极过程，而且同时改变了腐蚀反应的阴极过程；在反应初始阶段EIS具有2个时间常数，电极反应由活化控制，随着腐蚀的进行，腐蚀产物膜越来越厚，越来越致密，EIS的低频端出现Warburg阻抗与容抗的叠加，自腐蚀电位下的电极反应属于混合控制；溶液中是否含有Ca2+、Mg2+离子，在P110钢腐蚀成膜过程中EIS存在一定的差别，并且使阻抗谱拟合结果在相同的腐蚀时间内产生很大的变化.      

模拟体液法合成晶须状类骨纳米羟基磷灰石的研究

通过增加模拟体液中钙盐和磷盐的浓度,在模拟体液中合成了晶须状类骨纳米羟基磷灰石（HAp）粉体。利用X射线衍射（XRD）和红外吸收光谱（FTIR）分析粉体的物相组成和基本特征,利用透射电子显微镜（TEM）和高分辨透射电子显微镜（HRTEM）观察晶须的形貌、尺寸与生长方向,将粉体在500～900℃不同温度下热处理,研究其热稳定性。结果表明,晶须状羟基磷灰石的平均长径比为25：1（长100nm,直径4nm）,晶须沿c轴方向生长;热处理温度超过700℃,羟基磷灰石易发生分解。     

异步轧制对表面纳米化316L不锈钢组织和性能的影响

采用表面机械研磨处理(SMAT)在316L不锈钢上制备出纳米结构表层,然后在室温对其进行80％形变量的异步轧制(CSR),研究了CSR处理后表层组织和性能的变化．结果表明：经过60min SMAT后,样品表面形成了一定厚度的纳米晶层,晶粒尺寸为10—30nm．对其进行80％形变量的CSR后,表层组织仍为纳米晶组织,但纳米晶尺寸更加均匀、细小(为5—15nm),表面粗糙度显著下降;纳米表层硬度略有提高,但基体硬度显著提高;在0．05mol／L H2SO4 0.25mol／L Na2SO4腐蚀介质中的耐腐蚀性能比SMAT后的样品有明显改善,但均低于原基材．     

Environmental effects on the stress corrosion cracking susceptibility of 3.5NiCrMoV steels in high temperature water

Constant elongation rate tests (CERTs) were carried out to investigate the effects of environmental factors of dissolved oxygen and temperature on the stress corrosion cracking (SCC) susceptibility of 3.5NiCrMoV turbine steels. Tests were conducted in pure water of various dissolved oxygen concentrations at temperatures of 50 °C-200 °C in the range of strain rates from 5 × 10⁻⁸/s to 1 ×  10⁻⁶/s. Dissolved oxygen significantly affected the SCC susceptibility of turbine steels in water. The SCC susceptibility of the turbine steels increases as the dissolved oxygen concentration in water increases. The elongation of the turbine steels tested in aerated water at 150 °C at a strain rate of 1 × 10⁻⁷/s decreased to half of that of the steels tested in deaerated water in the same test condition. And the SCC susceptibility of the steels increased with decreasing strain rate, and with increasing temperature. The increase of the SCC susceptibility of the turbine steels in the higher dissolved oxygen environment is considered to be due to the higher content of dissolved oxygen enhancing the reduction reactions of oxygen on the metal surfaces (cathode) and accelerating the dissolution rate at the crack tips (anode) by galvanic attack of an aeration cell.