以蔗糖为前驱体制备TiC/Fe复合涂层

以TiFe粉和蔗糖为原料,通过蔗糖的热分解碳化制备Ti-Fe-C系反应热喷涂复合粉末,利用普通氧乙炔火焰喷涂成功制备出TiC/Fe复合涂层.采用XRD、SEM和TEM等对喷涂粉末和涂层的组织结构、涂层中的TiC颗粒进行了分析.研究结果表明:TiC/Fe复合涂层主要由TiC颗粒均匀分布于Fe基体中的复合强化片层构成,片层中TiC颗粒呈球形或近球形,粒径约为50nm;纳米级TiC颗粒增强的复合强化片层占涂层体积的60%以上.     

C/ Ti 原子比对反应火焰喷涂TiC/ Fe 复合涂层组织结构和硬度的影响

以TiFe 粉和碳的前驱体(石油沥青) 为原料, 用前驱体碳化复合技术制备了Ti-Fe-C 反应喷涂复合粉末, 并采用普通火焰喷涂技术成功制备了TiC/ Fe 陶瓷金属复合涂层。研究了不同C/ Ti 原子比对反应火焰喷涂TiC/ Fe 复合涂层相组成、显微结构和硬度的影响。结果表明, 前驱体碳化复合技术制备的Ti-Fe-C 系反应喷涂复合粉末中C/ Ti 原子比是影响涂层相组成、显微结构和硬度的关键因素。C/ Ti 原子比不同, 涂层的相组成和硬度不同; 随着C/ Ti 原子比增大, 涂层中TiC 团聚富集区增大, 涂层的孔隙率也随之增大。      

反应火焰喷涂TiC/Fe复合涂层显微结构研究

采用前驱体碳化复合技术制备Ti-Fe-C系反应喷涂复合粉末,通过反应火焰喷涂技术成功制备了TiC/Fe基金属陶瓷复合涂层.利用XRD和SEM对喷涂粉末和涂层的成分、组织结构进行了分析,考察了喷涂粉末粒度、Ti的加入方式对涂层组织结构的影响.研究结果表明:所制备的TiC/Fe复合涂层由不同含量TiC颗粒分布于晶粒内部而形成的晶内型复合强化片层组织叠加而成,TiC颗粒呈纳米级;喷涂粉末粒度较大时,制备的涂层中出现有害相Fe2Ti,片层厚度较大,孔隙率高;以纯Ti粉为Ti源制备的喷涂粉末和以TiFe粉为Ti源制备的喷涂粉末相比较,其涂层中硬质相TiC含量较少,孔隙率较大.     

Ni对TiC-Ni超音速火焰喷涂层组织和耐磨性的影响

Ni对Ti-Ni-C体系SHS反应中的热力学与动力学均有重要影响,Ni在超音速火焰喷涂合成中的作用尚不明确.利用超音速火焰喷涂合成技术制备了3种不同Ni含量的TiC-Ni金属陶瓷涂层,并对涂层进行了组织和性能研究.结果表明,Ni在喷涂过程中起到了吸收反应热、减缓喷涂合成过程中粉末组分的氧化、并在涂层中黏结相金属的作用.原料中的Ni含量对涂层的组织和性能影响较大,Ni含量低涂层中含有大量氧化物,且组织疏松、滑动磨损性能差;随着Ni含量升高到40%时,涂层的氧化物含量降低,滑动磨损性能增强; Ni含量过高,涂层中Ni片层增多,硬质相间距加大,涂层的耐磨损性能有所降低.     

反应等离子喷涂TiC/Fe涂层的摩擦磨损性能研究

采用等离子喷涂前驱体热分解技术制备的Fe-Ti-C系反应热喷涂粉末,在低碳钢基体上沉积TiC/Fe金属陶瓷复合涂层.利用SEM和X射线衍射仪对涂层的显微组织结构、磨损表面及其相组成进行分析;采用SRV型往复式摩擦磨损试验机评价喷涂涂层的摩擦磨损性能.结果表明: TiC理论含量为53%(质量分数)TiC/Fe金属陶瓷涂层的耐磨粒磨损性能较好,相比基体提高了约25倍;反应等离子喷涂TiC/Fe陶瓷涂层的磨损机制主要为粘着磨损和轻微的剥落.     

粉末状态对超音速喷涂合成TiC-Ni涂层组织和性能的影响

以Ti粉、Ni粉和石墨为原料通过PVA制粒和混合制粒制备两种喷涂粉末.研究表明:制粒方式在超音速火焰喷涂对涂层组织和耐磨性能有很大影响.PVA制粒粉末进行喷涂,涂层的相组成为TiC、Ni和少量Ti与Ni的氧化物,组织致密具有典型的层状涂层结构特征,涂层耐冲蚀磨损性能较强;混合制粒由于在火焰气流中缺乏SHS反应的条件,粉末喷涂后涂层中含有大量的Ti和Ni的氧化物和少量的粘结相Ni,具有较多的孔洞涂层组织疏松,耐冲蚀磨损性能较差.     

反应等离子喷涂TiC/ Fe-Ni复合涂层及其耐冲蚀性能

以TiFe粉、Ni粉和蔗糖(碳的前驱体)为原料,通过蔗糖的热分解碳化制备Ti-Fe-Ni-C系反应热喷涂复合粉末,并利用等离子喷涂制备了TiC/Fe-Ni复合涂层。复合涂层主要由TiC颗粒均匀分布于(Fe、Ni)固溶体中形成的复合强化片层构成,片层中TiC颗粒呈球形或近球形,粒度为亚微米级和纳米级。TiC/Fe-Ni复合涂层的耐冲蚀磨损性能研究表明：涂层冲蚀失重率随攻角的增大而增加,表现出脆性材料冲蚀特性,但冲蚀失重率对攻角不敏感,涂层具有较好的塑性与硬度的配合;复合涂层的耐冲蚀磨损性能优于相同工艺条件下制备的C_r2C₃/Ni-Cr复合涂层,约为20G钢的2倍以上。     

激光熔覆原位TiC/Fe复合涂层增强相形成机制研究

激光熔覆技术在制备原位自生颗粒增强金属基耐磨复合涂层领域具有良好的应用前景。以廉价钛铁和石墨为熔覆粉末,采用横流CO2激光器在低碳钢基体上制备了TiC增强Fe基复合涂层,并对涂层物相组织和TiC增强相的形成机制进行了研究。结果表明,增强相TiC通过原位冶金反应形成,在熔体的冷却过程中析出长大,具有树枝晶和鱼骨状两种形态。树枝晶形态的TiC为熔体先析出相,其生长形态受界面前沿成分过冷和晶体生长习性控制。鱼骨状TiC由δ-Fe和TiC的准共晶反应形成,溶质原子扩散特征和晶面能决定了共晶TiC的最终鱼骨状形貌。均匀弥散分布的TiC增强相有助于提高涂层的耐磨损性能。     

Q235低碳钢表面等离子熔覆TiB2-TiC/Fe复合涂层及耐磨性

采用等离子熔覆技术,以Fe55、Ti、B₄C混合粉末为原料,在Q235低碳钢表面获得了TiB₂-TiC/Fe复合涂层,并分析了涂层的物相组成、组织结构,测试了显微硬度和摩擦磨损性能,探讨了其磨损机制。TiB₂-TiC/Fe复合涂层的主要物相为TiB₂、TiC、α-Fe,其中TiB₂呈多边形和矩形,TiC则呈不规则块状;随着原始粉末中Ti、B₄C含量的增加,TiB₂、TiC尺寸逐渐增大,TiB₂-TiC/Fe涂层与基体之间结合紧密,呈冶金结合;随着TiB₂-TiC/Fe复合涂层陶瓷相含量的增加,涂层硬度和耐磨性显著提高,当陶瓷相含量增加到一定程度（35wt%）时,涂层耐磨性能有所降低,TiB₂-TiC/Fe复合涂层的磨损方式主要是磨粒磨损和剥层磨损。Ti+B₄C陶瓷相含量为30wt%的等离子熔覆涂层耐磨性能较好,约为Q235钢基体的7倍,当Ti+B₄C含量持续增加时,TiB₂、TiC尺寸增大、缺陷增多,最终使TiB₂-TiC/Fe复合涂层耐磨性降低。     

铁基复合材料涂层的原位反应合成

本文利用熔铸法研究了铁基复合材料的反应合成工艺和显微组织.结果表明:用液相原位反应合成法制备TiC/Fe基复合材料涂层是可行的;反应合成的TiC颗粒增强的Fe基复合材料涂层与基体没有明显的界面,涂层与基体结合状态良好;保温时间是影响TiC颗粒的大小、数量、及涂层厚度的重要因素之一.基体合金中含Ti为4%的样品保温2分钟后涂层厚度约为250μm,而保温7分钟后涂层厚度约为400μm,运用动力学计算对涂层厚度进行了理论计算,计算结果与实验结果的变化规律相似.     

杂质对氧化锆热障涂层性能的影响

降低热障涂层面层中的低熔点杂质含量, 可提高涂层的高温稳定性和延长服役寿命。SiO₂、Al₂O₃和Fe₂O₃是氧化钇稳定氧化锆(Yttria-Stabilized Zirconia, YSZ)热障涂层中几种常见的低熔点氧化物杂质, 均会对涂层的性能产生一定的影响。本研究采用大气等离子喷涂法, 制备SiO₂、Al₂O₃和Fe₂O₃的含量从小于0.01wt%增加至1.00wt%的YSZ热障涂层。采用扫描电镜(SEM)和透射电镜(TEM)研究了上述涂层的微观结构; 采用激光热导仪测试了涂层的热扩散系数和抗热震次数。研究结果表明, 低熔点氧化物杂质对YSZ涂层的导热性、热处理状态的孔隙率具有明显影响, 且更容易引起涂层的热震失效。当杂质氧化物含量在小于0.2wt%范围内变化时, 涂层的性能变化更为显著。     

A survey of test methods for scale adhesion measurement

Abstract

The spallation of oxide scales from the steam side of tubes in power generation boilers can severely limit component life time. The process involves through scale cracking and crack propagation at or parallel to the scale/alloy interface. Many techniques have been developed in the past two decades to assess the interfacial fracture toughness of brittle coatings on ductile substrates. Analyses from fracture mechanics approaches also allow for quantitative determination of the fracture toughness, which can be used for life time prediction modelling. This paper gives an overview on techniques that have been used on thermally grown oxides, such as Ni, Fe, Ti, Al, and Cr oxides and spinels, and compare the results obtained on each type of oxide system from different techniques. In doing so, the limitations of each technique are illustrated. The methods discussed are flexure, scratch, indentation, tensile and compression tests and those that perform direct analysis of the spallation process. The data on steam grown oxide is sparse, but the test methods discussed could all be applied to these scale types.     

Role of rare earth oxide coatings on oxidation resistance of chromia-forming alloys

Rare earths (RE) have been used to increase high temperature oxidation resistance of chromia and alumina forming alloys. The RE can be added as elements (or oxides) to the alloys or applied as oxide coatings to the alloy surface. This paper presents the effect of different RE oxide coatings and lanthanum chromite coatings on the high temperature oxidation behavior of Fe20Cr and Fe20Cr4Al alloys. The oxidation resistance of the Fe20Cr alloy increased with increase in ionic radius of the RE element in the coating. The RE oxides decreased chromia growth rate more than alumina growth rate. In extended cyclic oxidation tests that were carried out from peak temperatures of 900 °C, 1,000 °C and 1,100 °C to room temperature at cooling rates of 300 °C/s and 1,000 °C/s, the La₂O₃ coating increased cyclic oxidation resistance of the Fe20Cr alloy significantly more than the Pr₂O₃ coating. The role of RE in increasing overall oxidation resistance of chromia forming alloys is discussed.     

The influence of composition and process parameters on the microstructure of TiC-Fe coatings obtained by reactive flame spray process

It has been proved that TiC-Fe fine-grained multiphase and multilayer coatings, composed of alternate TiC-rich and TiC-poor lamellae with different microhardness, can be obtained by reactive flame spray technology using ferrotitanium and graphite as the starting materials. This study was undertaken to assess the influence of composition and process parameter on the microstructure of the coatings. It is found that parameters related to the melting and reaction of the reactive micropellets are the factors influencing the hardness of TiC-rich layers. A high hardness can be favored by more titanium reacted with graphite (that is, less Fe content and more C/Ti atomic ratio within the reactive micropellets), smaller micropellets and properly longer spray distance. Among all the variables considered, Fe content (or the expected TiC content) and spray distance are the main parameters to affect the microstructure of the coatings. Because the hardness of the stacking multiphase layers containing very fine and rounded TiC particles depend on the composition and process parameters, the TiC-Fe coatings could be tailored to meet different applications, particularly those needed resistance to crack propagation.     

Effect of process parameters on coating composition of cathodic-plasma-electrolysis-treated copper

Cathodic plasma electrolysis is a novel technique to form nanostructured layers on metallic surfaces by application of high voltage in a suitable aqueous electrolyte. In the present study, copper is treated by plasma electrolysis in 50 vol% ethanol electrolyte and coatings comprising carbon nanostructure and copper oxide are formed on the copper. The effect of some process parameters such as electrical conductivity, volume and temperature of electrolyte and ratio of anode to cathode surface area on current–voltage behaviour and subsequently coating compositions are investigated at 150 V deposition voltage. The composition and morphology of these coatings are characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Different current–voltage behaviours, temperatures of substrate and the contents and energies of radicals and ions around the substrate by changes in the mentioned parameters cause different compositions from 100 vol% copper oxide to different ratios of copper oxide to carbon, the structure changing from amorphous to graphitic structure in carbon and amorphous to cubic morphology in copper oxide on the substrate. Therefore, the understanding of cathodic plasma electrolysis can be developed.     

The effect of anodising on the fatigue performance of self-tapping aluminium screws

Self-tapping aluminium screws are an innovative joining technology for the assembly of lightweight components in industrial scale. It has been established in the past that porous anodic oxide coatings in many cases reduce the fatigue strength of specimens without notches. In the present work, the fatigue behaviour of notched specimens, i.e. self-tapping screws made from aluminium alloys EN AW-6056, 6082 (both in a conventional state and in a fine-grained state produced by equal channel angular pressing – ECAP) and 7068 with and without oxide coatings is examined. The coatings are produced by hard anodising and are necessary for the thread-forming process during assembly. While the coatings do not affect the static tensile strength, they reduce the fatigue strength for the specimens of the 6056 and the 6082 alloy. For the 7068 alloy a slight increase in fatigue strength is discovered on a low load horizon. The scatter of endured fatigue cycles until fracture of specimens is generally reduced by the anodic oxide coatings.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN (0≤x≤0.47) Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900 ℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3 Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the Al content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Ferromagnetic composite coatings on carbon fibers

Alumina- and titania-based composite coatings containing ferromagnetic nanoparticles have been produced on UKN-5000P carbon fibers by an in situ organo-inorganic hybrid sol-gel process using appropriate aqueous metal chloride solutions containing Fe(III) and Co(II). The morphology, phase composition, and elemental composition of the coatings have been studied by high-resolution electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. The results demonstrate that the oxide coatings containing ferromagnetic nanoparticles are uniform in thickness along and across the fibers and adhere well to the fiber surface. The coatings range in thickness from 100 to 500 nm. In all of the systems studied, the coatings produced on carbon fibers differ in phase composition from powders prepared from identical hydrosols.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN （0≤x≤0.47） Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.