Dry Sliding Behavior of Sub-Micrometer-Sized Suspension Plasma Sprayed Ceramic Oxide Coatings

Almost half of the energy produced by an automotive engine is dissipated by friction in the cylinders, the clutch, etc. In the context of reduction of the emissions of greenhouse gases (GHGs) to mitigate climate global warming (CGW), reduction of energy losses due to friction is a critical issue. Surface treatments appear in such a context, as never than before, to be able to provide pertinent solutions to improve sliding behavior of mechanical parts. Numerous studies have clearly shown that decreasing the scale of coating structure below the micrometer scale was leading to an improvement of its tribological behavior in terms of friction coefficient and wear rate thanks to improved mechanical properties, the toughness in particular. Suspension Plasma Spraying (SPS) appears as a thermal spray process to be able to manufacture thick (i.e., a few tens of micrometers) coatings exhibiting a sub-micrometer-sized or even a nanometer-sized architecture, while keeping the versatility and flexibility of the thermal spray routes: i.e., the ability to process a wide range of material natures onto a wide range of substrate materials of various geometries. This article aims at studying the tribological behavior of several ceramic oxide composite coatings under dry conditions. The structural scale and the effect of composition are considered in particular.     

氮化钛 / 氧化钛复相陶瓷涂层的干滑动摩擦磨损性能

目的研究等离子喷涂Ti N/Ti O复相陶瓷涂层的微观组织结构、显微硬度及干滑动摩擦磨损行为和机理。方法采用等离子喷涂技术,在45#钢表面制备Ti N/Ti O复相陶瓷涂层。分析涂层的相组成,测试涂层的硬度。通过磨损试验研究Ti N/Ti O复相陶瓷涂层的磨损行为,并观察涂层的磨损形貌,测试磨损表面的成分组成,探讨Ti N/Ti O复相陶瓷涂层的磨损机理。结果 Ti N/Ti O复相陶瓷涂层均匀致密,平均厚度为350μm,具有明显的层状结构,孔隙率为4.3%,显微硬度为1444HV0.1。在载荷30~50 N、转速370~1102 r/min的范围内,Ti N/Ti O复相涂层与GCr15对磨的摩擦系数为0.0963~0.2778,磨损量为1.32~6.8 mg。随着载荷的增加,摩擦系数下降;随着载荷和转速的增加,磨损量增加。结论等离子喷涂制备的Ti N/Ti O复相涂层组织致密,显微硬度高,在低速低载荷时表现出较好的耐磨性,但随着载荷和转速的增加,耐磨性降低。涂层的磨损机制主要为磨粒磨损和粘着磨损。     

高性能陶瓷涂层及其制备工艺发展趋势

从功能、用途方面分类综述了耐磨、耐蚀以及热障三大类高性能陶瓷涂层,在此基础上,介绍了高性能陶瓷涂层常用的制备工艺,重点探讨了不同制备方法的特点和适用场合,指出了制备方法的发展方向。物理气相沉积技术(PVD)制备的陶瓷涂层纯度高、致密性好,并且与基体结合牢固,但其生产成本高,生产效率低,因此物理气相沉积技术向着高效率、低成本的方向发展。化学气相沉积技术(CVD)制备的陶瓷涂层涂覆率高、致密性好,但其反应温度高,并且伴随着有毒有害气体产生,因此化学气相沉积技术向着低温、环保的方向发展。等离子喷涂技术(PS)制备陶瓷涂层成本低、效率高、适应性强,但涂层孔隙率高,并且涂层与基体的结合强度低,因此等离子喷涂技术向着高致密、高结合强度的方向发展。激光熔覆技术制备的陶瓷涂层组织细小、力学性能优良,但其操作工艺复杂,产品质量很难控制,因此激光覆熔技术向着工艺简单、质量可控的方向发展。最后,展望了高性能陶瓷涂层及其制备工艺的发展方向和可能的研究内容。     

Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications

Improvement in the performance of thermal barrier coatings (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria-stabilized zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures. The objective of this work was to investigate different multilayered TBCs consisting of advanced topcoat materials fabricated by suspension plasma spraying (SPS). The investigated topcoat materials were YSZ, dysprosia-stabilized zirconia, gadolinium zirconate, and ceria–yttria-stabilized zirconia. All topcoats were deposited by TriplexPro-210^TM plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high-temperature applications.     

微弧陶瓷化在耐磨耐热件上的应用

采用微弧陶瓷化技术对发动机铝活塞及电辐射管热强钢外套管进行表面改性研究。结果表明，铝活塞第一环槽陶瓷化后，与活塞环的侧隙磨损量减少3～4倍，热浸铝后经陶瓷化处理的电辐射管热强钢外套管耐热温度提高400℃，寿命提高2倍以上。     

Optimization of Arc-Sprayed Ni-Cr-Ti Coatings for High Temperature Corrosion Applications

High Cr content Ni-Cr-Ti arc-spray coatings have proven successful in resisting the high temperature sulfidizing conditions found in black liquor recovery boilers in the pulp and paper industry. The corrosion resistance of the coatings is dependent upon the coating composition, to form chromium sulfides and oxides to seal the coating, and on the coating microstructure. Selection of the arc-spray parameters influences the size, temperature and velocity of the molten droplets generated during spraying, which in turn dictates the coating composition and formation of the critical coating microstructural features—splat size, porosity and oxide content. Hence it is critical to optimize the arc-spray parameters in order to maximize the corrosion resistance of the coating. In this work the effect of key spray parameters (current, voltage, spray distance and gas atomizing pressure) on the coating splat thickness, porosity content, oxide content, microhardness, thickness, and surface profile were investigated using a full factorial design of experiment. Based on these results a set of oxidized, porous and optimized coatings were prepared and characterized in detail for follow-up corrosion testing.     

激光熔覆Ni基微-纳米WC金属陶瓷涂层组织及干滑动磨损性能

在45钢表面进行添加微一纳米WC颗粒的镍基自熔粉末激光熔覆处理.得到不同Ni基WC合金涂层.对熔覆层进行显微组织观察、硬度测定以及室温千摩擦磨损试验.结果表明,纳米品WC的加入能改善涂层的耐磨性能,在本试验条件下,当添加的纳米级WC和微米级WC各为15%时.涂层耐磨性能最佳;但纯纳米晶WC增强涂层耐磨性不佳,其主要磨损破坏方式随涂层中WC晶粒尺寸变化而有所变化.     

The Properties and Applications of MoS_2/Ti Composite Coatings in Dry Cutting and Forming

MOLYBDENUM DISULFIDE COATIGS have beensuccessfully used in vacuum and aerospaceenvironments in the past30years.In recent years,theapplication of MoS2coatings in ambient or high humidenvironments has been drawing increasing attentions.The main obstacle to the use of MoS coating inambient conditions is its sensitivity to humidity.Fig.1shows the cases that may degrade the humidityresistance of MoSx coatings,such as the columnarstructure,low density,edge orientation of the coatings;and…     

陶瓷刀具高速干切削加工数值仿真研究

陶瓷刀具在高温作用下会产生自润滑现象,可起到减摩、抗磨作用.论文以Al2O3陶瓷刀具为例,在高温下刀具表面产生自润滑薄膜,利用有限元分析软件DEFORM-3D,建立高速切削AlSI——1045模型,分析Al2O3陶瓷刀具在高速切削加工时,产生自润滑现象所需切削速度,以及在高速切削时,刀具表面的主切削力、应力分布、温度分布和刀具的磨损状态等.研究表明:当切削速度为270m/min,时,刀具表面温度高达842℃,能够产生自润滑现象.     

一种高性能熔模铸造复合型壳的制备工艺

为实现近净形熔模铸造,介绍了一种高性能熔模铸造复合型壳的制备工艺,其中第1~3层使用硅酸乙酯涂料,背层使用硅溶胶涂料。此工艺避免了硅酸乙酯-硅溶胶交替硬化复合型壳工艺由于硅酸乙酯涂料与硅溶胶涂料相互污染,而使涂料使用寿命缩短的情况,提高了涂料的利用率,有利于生产成本的降低,所得铸件精度可以达到CT5级,表面粗糙度可以达到Ra0.8~1.6μm。     

SiCp/A356复合材料高温干滑动摩擦磨损特性研究

借助UMT-2型摩擦磨损试验机详细研究了转速对 SiCp/A356复合材料干滑动摩擦磨损特性的影响,并用SEM、EDS和奥林巴斯激光共焦扫描显微镜观察并分析了其高温摩擦磨损行为。结果表明：铸态材料的磨损率增加幅度和摩擦系数曲线波动较大;T6态材料的磨损率增加幅度和摩擦系数曲线波动较小,表现出优异的摩擦性能。铸态材料的磨损机理主要由低转速时的氧化磨损和剥离磨损转变为高转速时的粘着磨损,而T6态材料主要由低转速时的氧化磨损转变为高转速时的剥离磨损和磨粒磨损。高转速区时,铸态材料的磨损断面中出现裂纹,而T6态材料只是存在简单的磨削痕迹和颗粒脱落现象,热处理后复合材料的高温耐磨性能明显提高。     

高频淬火对FeNiMoCuCr粉末烧结钢干摩擦磨损性能的影响

采用销盘式磨损试验机研究了FeNiMoCuCr系粉末烧结钢经表面高频淬火后,在干摩擦磨损条件下的磨损性能,并借助于扫描电镜观察和分析了磨损形貌,探讨其摩擦磨损机制。结果表明,试验材料的磨损率在磨损开始阶段,随摩擦滑移距离的增加而增加,而后逐渐趋于稳定;高频淬火处理后的FeNiMoCuCr粉末烧结钢的耐磨性高于烧结未淬火的磨损率,扫描电镜显示干摩擦磨损形貌为微观犁沟和塑性变形,粘着磨损和氧化磨损是主要的磨损机制。     

超高分子量聚乙烯/石墨烯复合涂层制备及其在海洋装备防护中的应用

目的采用热喷涂技术制备涂层,通过材料选择和结构设计,有效延缓海水对金属基底的腐蚀和冲蚀,并抑制海洋材料表面生物污损等对海洋材料的严重破坏。方法采用高能球磨法制备了聚乙烯-石墨烯(UHMWPE-graphene)复合粉末,用火焰喷涂技术在E235B碳钢基底表面制备UHMWPE和UHMWPE-graphene复合涂层。通过扫描电子显微镜和透射电子显微镜对原始粉末和涂层微观组织进行表征,并通过摩擦磨损实验、电化学测试、生物污损检测,分别评价涂层耐海水冲刷性能、耐腐蚀性能以及抗生物污损特性。结果相对于碳钢和UHMWPE涂层,UHMWPE-graphene复合涂层的腐蚀电位提高和腐蚀电流减小,预示着样品的耐腐蚀特性增强。由于UHMWPE-graphene复合涂层呈现疏水性以及更低的表面能,使其表现出优异的抵抗海藻贴附的能力。添加石墨烯的复合涂层的摩擦系数和磨损率比纯UHMWPE涂层均有一定程度的降低。添加石墨烯质量分数为0.5%时,涂层的摩擦系数由0.236降低到0.195,且磨损率下降了约26%。结论利用火焰热喷涂技术在碳钢表面成功制备了组织致密的UHMWPE涂层、UHMWPE-0.2%graphene和UHMWPE-0.5%graphene复合涂层。石墨烯的添加,能够有效提高涂层在模拟海洋环境中的耐蚀性、抗生物污损性及耐磨性。     

高性能涂层实验室加速老化改进试验方法的研发

目的改进实验室加速老化与亚热带自然老化之间的相关性及其预测能力。方法包括美国福特、波音、巴斯夫和亚太拉斯等在内的多家公司耗时近10年合作研发改进试验方法。在自然和加速老化的条件下,使用各种不同的测试周期,对20多种已知户外老化性能的汽车面漆/清漆涂层系统及几种单涂层系统进行测试。借助光谱技术跟踪分析了样品涂层中作为光氧化降解和水解降解标记的几个关键峰值。将老化后的涂层系统制成5?m厚超薄切片,跟踪研究其化学变化以及紫外吸收剂浓度的变化。结果加速老化光源与户外地面阳光在质和量上的光谱匹配度,尤其是紫外波长截止点的匹配,是改变涂层降解过程化学反应的关键。研发出一种特殊滤镜,克服了现有光源系统的局限性。对比佛罗里达自然老化实验发现,现有实验室试验方法无论在质还是量上,水分输送均不够充足。对测试周期加以修改,直至其水分吸收与释放和户外昼夜模式相匹配,并对自然条件下的正常波动给予额外补偿,包括长时间浸透让涂层达到水饱和以及随后的干燥和热冲击循环。最后研究了样品温度的影响,包括热机械应力以及昼夜循环对涂层水动力体积的影响,建立了分段式辐照度和温度循环周期,以更好模拟温度对次级涂层降解反应及物理老化的影响。结论新的测试方法显著改善了所有样品与户外自然降解时所发生化学反应的相关性,忠实再现了涂层系统在佛罗里达自然老化时产生的物理变化(如剥离、附着力损失、开裂和起泡),并且具备更好的加速性,达到佛罗里达自然曝晒2~5年的同等效果,新试验比现行方法快大约40%。新试验方法最终被建标为ASTM D7869-13《交通工具用涂料氙灯老化测试标准-增强光照及水曝露》。     

Corrosion Testing of Ni Alloy HVOF Coatings in High Temperature Environments for Biomass Applications

This paper reports the corrosion behavior of Ni alloy coatings deposited by high velocity oxyfuel spraying, and representative boiler substrate alloys in simulated high temperature biomass combustion conditions. Four commercially available oxidation resistant Ni alloy coating materials were selected: NiCrBSiFe, alloy 718, alloy 625, and alloy C-276. These were sprayed onto P91 substrates using a JP5000 spray system. The corrosion performance of the coatings varied when tested at ~525, 625, and 725 °C in K₂SO₄-KCl mixture and gaseous HCl-H₂O-O₂ containing environments. Alloy 625, NiCrBSiFe, and alloy 718 coatings performed better than alloy C-276 coating at 725 °C, which had very little corrosion resistance resulting in degradation similar to uncoated P91. Alloy 625 coatings provided good protection from corrosion at 725 °C, with the performance being comparable to wrought alloy 625, with significantly less attack of the substrate than uncoated P91. Alloy 625 performs best of these coating materials, with an overall ranking at 725 °C as follows: alloy 625 > NiCrBSiFe > alloy 718 ? alloy C-276. Although alloy C-276 coatings performed poorly in the corrosion test environment at 725 °C, at lower temperatures (i.e., below the eutectic temperature of the salt mixture) it outperformed the other coating types studied.     

金属/陶瓷功能梯度涂层工艺的应用现状

本文综述了功能梯度涂层的多种制备工艺,包括各工艺的基本原理、特点和应用现状,提出了现存功能梯度涂层工艺中存在的主要问题。     

Atmosphere Plasma-Sprayed Carbon Nanotubes/Cordierite Nanocomposite Coatings for Microwave Absorption Applications

Multi-walled carbon nanotubes (MWCNTs)/cordierite (MAS) nanocomposite coatings with different MWCNT contents were prepared via atmosphere plasma spraying method. The characteristics of the MWCNTs/MAS powders and as-sprayed coatings, such as microstructure and phase constitution, were observed and measured. The dielectric properties and microwave absorption properties of MWCNTs/MAS powders and nanocomposite coatings have been investigated at the frequency of 8.2-12.4 GHz with different MWCNT contents and sample thicknesses. When the MWCNT content increased to 7%, the nanocomposite coating revealed the highest dielectric constant and optimal microwave absorption property. Further increase in MWCNT content led to severe oxidation of MWCNTs during the plasma spray process, which resulted in lower dielectric constants and poor microwave absorption property. Moreover, the sample thickness has a noticeable influence on the reflection loss (RL) of the MWCNTs/MAS coatings, and the coating of 2.4-mm thickness shows optical microwave absorption with a minimum RL of ?15.61 dB and bandwidth of 2.35 GHz.     

Nanostructural Characteristics of Vacuum Cold-Sprayed Hydroxyapatite/Graphene-Nanosheet Coatings for Biomedical Applications

Development of novel biocompatible nanomaterials has provided insights into their potential biomedical applications. Bulk fabrication of the nanomaterials in the form of coatings remains challenging. Here, we report hydroxyapatite (HA)/graphene-nanosheet (GN) composite coatings deposited by vacuum cold spray (VCS). Significant shape changes of HA nanograins during the coating deposition were revealed. The nanostructural features of HA together with curvature alternation of GN gave rise to dense structures. Based on the microstructural characterization, a structure model was proposed to elucidate the nanostructural characteristics of the HA-GN nanocomposites. Results also showed that addition of GN significantly enhanced fracture toughness and elastic modulus of the HA-based coatings, which is presumably accounted for by crack bridging offered by GN in the composites. The VCS HA-GN coatings show potential for biomedical applications for the repair or replacement of hard tissues.     

Performance of Bond Coats Modified by Platinum Group Metals for Applications in Thermal Barrier Coatings

We have investigated the partial replacement of Pt with other less expensive Pt group metals on the properties of γ′ + γ bond coats used in thermal barrier coatings (TBCs) deposited on a nickel-base superalloy. The microstructure, thermal stability, oxidation behavior and performance in TBC systems of bond coats synthesized with Pt + Ru, Pt + Ir and Pt + Rh are compared with those of a reference bond coat synthesized with Pt. Yttria-stabilized zirconia has been employed as top coat in all coating systems. It is shown that at high temperatures all bond coats are degraded by interdiffusion and oxidation, however, with different kinetics. The lifetime of each TBC system is found to be limited by the cohesion between the thermally grown oxide and underlying bond coat. Differences in the behavior of various bond coats are correlated with their properties. Among the three Pt group metals investigated, the properties of the Pt + Ru bond coat are shown to closely approach those of the Pt bond coat. It is concluded that Ru with much lower cost presents a potential candidate for reducing the consumption of Pt.     

Thermal Spray Coatings Engineered from Nanostructured Ceramic Agglomerated Powders for Structural,Thermal Barrier and Biomedical Applications: A Review

Thermal spray coatings produced from nanostructured ceramic agglomerated powders were tailored for different applications, some of which required almost completely opposite performance characteristics (e.g., anti-wear and abradable coatings). The influence of nanostructured materials on important areas, such as, thermal barrier coatings (TBCs) and biomedical coatings was also investigated. It was determined that by controlling the distribution and character of the semi-molten nanostructured agglomerated particles (i.e., nanozones) embedded in the coating microstructure, it was possible to engineer coatings that exhibited high toughness for anti-wear applications or highly friable for use as abradables, exhibiting abradability levels equivalent to those of metallic-based abradables. It is shown that nanozones, in addition to being very important for the mechanical behavior, may also play a key role in enhancing and controlling the bioactivity levels of biomedical coatings via biomimetism. This research demonstrates that these nanostructured coatings can be engineered to exhibit different properties and microstructures by spraying nanostructured ceramic agglomerated powders via air plasma spray (APS) or high velocity oxy-fuel (HVOF). Finally, in order to present readers with a broader view of the current achievements and future prospects in this area of research, a general overview is presented based on the main papers published on this subject in the scientific literature.