涂层金属的腐蚀机理研究

介绍了有机涂层下金属基体的腐蚀机理;论述了涂层金属的腐蚀类型。     

表面状态和处理对涂层下A3钢腐蚀和涂层失效的影响

采用模拟大气腐蚀装置，用挂片法研究了不同表面处 理和表面状态、不同湿度对涂层失效的影响.通过对基体金属的腐蚀形貌观察，微区元素分析，并结合傅利叶变换红外光谱(FTIR)，研究了金属在涂层下的腐蚀产物和涂层结构的变化.同时探讨了金属在涂层下的腐蚀和涂层失效机理.     

应用多重动电位扫描极化技术测评有机涂层／金属体系的耐腐蚀性

应用多重动电位扫描极化技术测评有机涂层／金属体系的耐腐蚀性林昌健（固体表面物理化学国家重点实验室，厦门大学厦门３６１００５）Ｔ．Ｎｇｕｙｅｎ（美国国家标准与技术研究院）１引言有机聚合物涂层／金属体系的腐蚀已成为腐蚀界的一个研究热点［‘－‘］．影响有机...     

耐液锌腐蚀涂层的研究现状

工业连续热浸镀锌生产线上,沉没辊、轴承等部件受到锌液的强烈腐蚀.耐液锌腐蚀涂层能够保护其免受液锌腐蚀的破坏.现有的耐液锌腐蚀涂层如金属涂层、金属陶瓷涂层、氧化物陶瓷涂层等耐液锌腐蚀寿命短、材质脆、易脱落,无法为部件提供有效保护.本文回顾了液锌对铁基合金的腐蚀机理,综述了耐液锌腐蚀涂层的研究现状.同时,文章指出了发展新型涂层材料和制备技术是未来耐液锌腐蚀涂层发展的一个必然趋势.     

金属包装材料涂层防腐技术

金属材料在包装领域保持着极大的生命力,但化学稳定性较差、耐腐蚀性差是金属包装材料存在的主要问题,利用涂层技术在金属表面覆盖涂层是防止金属包装材料腐蚀的有效方法.在分析金属包装材料的性能及防腐蚀方法的基础上,结合金属包装材料腐蚀防护问题,对主要的金属涂层防腐技术及涂料涂层防腐技术进行了介绍.展望了金属包装材料涂层防护的应用发展情况及动态;指出了涂层隔离防护并不能从根本上解决金属材料的腐蚀问题,研发新型耐腐蚀材料成为涂层防护技术的发展方向.     

燃气轮机在海洋环境下的热腐蚀与防护技术研究进展

针对海洋环境下舰船燃气轮机的热腐蚀现状,从热腐蚀的机理研究着手,基于不同阶段提出的热腐蚀模型理论,分析了高温和低温两种热腐蚀类型的发生过程和表现特征,指出热腐蚀实质上是以Na2SO4为主导的熔盐沉积共晶物与金属基体发生反应而导致金属材料加速氧化的过程。在此基础上,详细介绍了三种涂层防护技术—扩散涂层、覆盖涂层和热障涂层,并根据这三种涂层的发展阶段和功能特性,分析了其在制备工艺、作用机理和应用领域上表现出的差异性,重点强调了热障涂层(TBCs)在当前的发展境况。结合世界各国研究者开展的代表性工作,全面综述了国内外在舰船燃机热腐蚀防护领域的研究进展,重点描述了以硫酸盐为主的腐蚀介质中,金属材料的热腐蚀表现特征,并展示了数值模拟、热力学模拟等方法在热腐蚀研究上的应用案例。最后,对舰船燃气轮机涂层防护技术的发展方向进行了展望,提出发展新一代环障涂层(EBCs)是提高燃气轮机综合防护能力的有效技术手段。     

大气环境中涂层下金属的腐蚀和涂层的失效

综述了大气环境中腐蚀和涂层失效的机理，影响腐蚀失效的各种因素及研究方法和手段，展望了研究前景，老化和涂层下金属腐蚀是引起涂层失效两个重要的因素。老化为自由基机理，涂层下金属腐蚀为电化学反应机理。影响腐蚀失效的各种因素包括涂层性能，气体污染物，基体金属上可溶盐污染，基体金属表面状态和处理等。研究方法主要有电化学方法和光谱学方法，电化学方法中最主要的是电化学阻抗法，较新的是Kelvin扫描电极，光谱学方法包括红外光谱，激光拉曼光谱等。现代采用多种方法综合研究，并且倾向于使用原位在线测量技术。     

耐空蚀涂层及其研究进展

螺旋桨、水轮机和水泵等过流部件在高速运转过程中会因空泡腐蚀而损坏,严重时会造成部件提前失效,引发安全事故。所谓空泡腐蚀,是指过流部件附近液体因局部压力下降而引起气泡的形核与长大,当气泡流向高压区时发生溃灭,所产生微射流与冲击波对部件表面造成损伤。目前,在表面制备防护性涂层是部件抵御空蚀损伤较为经济且行之有效的方法。总结了多种国内外用于空蚀防护的涂层材料,并根据抗空蚀原理将其分为两种,一是为通过自身较高的硬度来抵御空泡冲击的高硬度涂层,如大多数的金属、陶瓷材料以及基体的直接硬化改性处理。其中金属涂层及表面硬化改性处理会在抗空蚀领域广泛应用,但仍需要解决腐蚀对空蚀的加剧作用;至于金属陶瓷涂层,热喷涂工艺下的颗粒难以完全熔化,制备的涂层呈现较高的孔隙率,且由于陶瓷颗粒与金属非冶金结合,因此在空蚀的作用下容易剥落。改善金属陶瓷涂层的硬度与韧性,增强涂层与基体间的结合力,降低涂层的孔隙率是未来的研究方向。另外一种是具有良好韧塑性的高弹性涂层,通过吸收空蚀冲击波与微射流的机械冲击能量来延长空蚀孕育期,降低空蚀破坏,如形状记忆合金和聚合物有机涂层。其中有机涂层极大地降低了腐蚀的作用,是未来抗空蚀涂层...     

金属表面腐蚀防护的复合涂层技术在徐州问世

采用涂层技术对金属表面进行腐蚀防护的方法由来已久,如各类镀层、金属热喷涂涂层、有机涂料涂层等,都取得了较好的防护效果。与铁比,锌、钼等都是活性很强的金属,采用热喷涂锌、钼或其合金形成金属涂层可对铜铁金属形成良好的保护,但由于金属热喷涂形成的金属涂层是由熔化金属雾化成4-40μm的微粒而黏附于铜铁基材的表面上,涂层结构较疏松,腐蚀介质可以很轻易地渗透浸入到钢铁基材,形成腐蚀,其表面必须采用封闭涂料进行封闭处理。     

表面状态和处理对涂层下A3钢腐蚀和涂层失效的影响

采用模拟大气腐蚀装置，用挂片法研究了不同表面处理和表面状态、不同湿度对涂层失效的影响．通过对基体金属的腐蚀形貌观察，微区元素分析，并结合傅利叶变换红外光谱(FTIR)，研究了金属在涂层下的腐蚀产物和涂层结构的变化．同时探讨了金属在涂层下的腐蚀和涂层失效机理．     

Rheology Feature of Simple Metal Melt

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 k Hz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more {110}116 grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, {110}116 can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of {110}116 grains and therefore enhance the sharpness of Goss texture.     

Laser Cladded TiCN Coatings on the Surface of Titanium

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80?滋m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

Growth Morphologies of a Binary Alloy with Low Anisotropy in Directional Solidification

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.