Corrosion behavior of HVOF coated sheets

High velocity oxygen-fuel (HVOF) thermal spray coating finds application in industry due to its superior resistance to corrosion and thermal loading. In the HVOF process, the metallic powders at elevated temperature are sprayed at supersonic speed onto a substrate material. The powder granules sprayed impact onto each other, forming a mechanical bonding across the coating layer. In most of the cases, the distances among the particles (powder granules sprayed) are not the same, which in turn results in inhomogeneous structure across the coating layer. Moreover, the rate of oxidation of the powder granules during the spraying process varies. Consequently, the electrochemical response of the coating layer surfaces next to the base material and free to atmosphere differs. In the current study, the electrochemical response of a coating sheet formed during HVOF thermal spraying was investigated. NiCrMoNb alloy (similar to Inconel 625) wass used for the powder granules. Thermal spraying was carried out onto a smooth surface of stainless steel workpiece (without grid blasting), and later the coating layer was removed from the surface to obtain the coating sheet for the electrochemical tests. It was found that the corrosion rate of the smooth surface (surface next to the stainless steel surface before its removal) is considerably larger than that corresponding to the rough surface (free surface) of the coating sheet, and no specific patterns were observed for the pit sites.     

提高油气水井工具抗冲蚀性能的方法

为提高奥氏体不锈钢等材料加工的油气水井工具在高温、含砂等工况下的抗冲蚀性能,使用钴基金属粉末+10%WC+3%Al为材料,利用激光熔敷技术在1Cr18Ni9Ti工具上制备了钴基金属陶瓷复合熔敷层,并对工具熔覆层进行冲蚀试验. 结果表明,获得的工具表面熔覆层致密均匀,与基体呈冶金结合,熔覆层可以大体分为上垂直于界面生长的平面晶和胞状晶区、向熔池中部过渡为多方向生长的树枝晶区、近表面平行于激光扫描速度方向生长的细小枝晶区. 冲蚀后的钴基熔覆层表面起伏很小,仅分布一些冲蚀凹坑和很小的犁沟,可以有效地提高油气水井工具的冲蚀性能及使用寿命.     

氢传感器用铂电极的制备及性能研究

采用浆料涂覆烧结法制备铂电极,对比了基材处理方式(磁控溅射/喷砂)、铂黑(Ptb)和氧化铂(PtO₂)粒径差异对电极形貌、附着力、方阻及电催化性能的影响。结果表明,基材采用磁控溅射法制备的涂层表面结构优于喷砂法的涂层,使其剥离强度均略高于喷砂处理的样品;针对于粉末粒度,需控制在一定范围内(即Ptb(350nm)和PtO₂(350nm)),其制备的涂层表面易形成蜂窝状或絮状的微连接结构,可显著降低方阻,提高其附着力。对结构和附着力较好的Ptb/Pt电极和PtO₂/Pt电极进行CV曲线分析,PtO₂/Pt电极的电催化性能优于Ptb/Pt电极。     

树脂基复合材料用陶瓷涂层防护性能分析

采用等离子喷涂铝粉作为打底材料在碳纤维增强聚酰亚胺复合材料（PMC）基体上制备了Al2O3和ZrO2轻质陶瓷防护涂层，测试了涂层的剪切结合强度、耐热循环性能、抗冲蚀性能、隔热性能。结果表明，等离子喷涂铝粉作打底层的涂层系统，性能优于电弧喷铝或电弧喷锌作打底层的涂层系统。带有Al2O3涂层的试样失重不到基体材料失重的1／3，Al2O3和ZrO2陶瓷涂层都可以为聚酰亚胺复合材料基体提供有效的冲蚀防护。Al2O3和ZrO2陶瓷涂层都可以为聚酰亚胺复合材料基体提供有效的隔热防护，ZrO2涂层隔热性能优于Al2O3涂层。     

粉末预置法电火花沉积WC-8Co涂层分析

针对传统电火花沉积技术存在电极制备工艺复杂、涂层存在较多裂纹及孔洞的不足,把WC-8Co粉末置于电极与基体之间的脉冲放电通道内,利用电火花沉积工艺制备了WC-8Co涂层.对比分析了新工艺与传统工艺制备的涂层表面形貌、显微组织及摩擦磨损性能.结果表明,用新工艺制备的涂层表面平整、粗糙度低、组织致密,与基体呈冶金结合.与传统工艺相比,新工艺制备的涂层有良好的耐磨粒磨损性能.用粉末预置法制备涂层能提高电火花沉积效率,适于制备大面积的涂层.     

Laser surface modification using Inconel 617 machining swarf as coating material

A single-stage, blown powder laser cladding process is used to deposit a protective layer of Ni-based alloy Inconel 617 on mild steel substrates. A Design of Experiments methodology is used to analyse the effects of the major laser cladding processing parameters on the deposited layer characteristics. Layer thickness, microstructure, dilution, elemental composition and corrosion resistance are analysed and correlated with the processing parameters and the overall effectiveness of the protective coating assessed. The work is different in that the protective material, usually in the form of costly powder, is in this case virtually cost-free and simply recycled from machining waste without any costly atomisation or similar process. The results show a number of significant relationships between the processing parameters and the effectiveness of the protective coating. The layer thickness and hardness were found to increase with the mass feed rate and decrease with an increase in laser power. A mainly columnar dendritic microstructure was observed in the clads. There was no evidence of significant bonding defects, trapped unmelted particles or porosity under most conditions. In all samples, the coatings displayed significant higher corrosion resistance than the mild steel sample.     

TiB_2/Cu涂层抗烧蚀性能研究

应用500WYAG固体激光器在纯铜表面成功地原位合成了TiB2/Cu复合涂层,采用自制设备对复合涂层进行抗电弧烧蚀性研究。结果表明,相对于纯铜,TiB2/Cu复合涂层的电弧烧蚀性显著降低,抗电弧烧蚀性能明显提高,熔覆层存在少量烧蚀区裂纹和孔洞。     

激光熔覆对Cu抗烧蚀性能的影响

应用激光熔覆法使Ti粉和B4C粉在铜基体表面发生原位反应形成了熔覆层,通过XRD分析确定了熔覆层相组成为TiB2/Cu。熔覆层试样和纯Cu的抗电弧烧蚀实验在自制设备上进行,并采用SEM观察了电弧烧蚀表面的形貌。研究结果表明,随着电弧烧蚀次数的增加,熔覆层试样表面电弧烧蚀和氧化现象并不明显,烧蚀孔洞少且小,没有液态金属喷溅现象;而纯铜试样表面变得较为粗糙,电弧作用的中心处烧蚀氧化严重,有大量的烧蚀坑存在,并且出现液态金属飞溅现象。因此,相对纯铜,TiB2/Cu复合涂层电弧烧蚀显著降低,抗电弧烧蚀性能明显提高。     

WC-Co-Cr涂层和0Cr13Ni5Mo基材的气体喷砂冲蚀行为

研究不同结构HVOF热喷WC-Co-Cr涂层和0Cr13Ni5Mo基材的冲蚀行为,重点分析高速粒子冲击下涂层孔洞和层状结构等缺陷在不同攻角下的作用,提出高攻角气体喷砂冲蚀模型,解释了WC-Co-Cr涂层和0Cr13Ni5Mo基材的冲蚀行为规律。结果表明:低攻角时,涂层与基材的损伤机制均以微切削去除为主,涂层还伴有少量剥落,WC-Co-Cr涂层的耐冲蚀性能一般优于基材,但高孔隙率涂层更易切削导致冲蚀率比基材高。随攻角增大,涂层冲蚀率呈上升趋势而基材冲蚀率下降。高攻角时,层状结构明显的涂层其裂纹更易在层间萌生和扩展导致片状剥落,高孔隙率反而有利于吸收冲击能量和抑制裂纹扩展;基材则出现严重塑性变形。在气体喷砂条件下,涂层的层状结构对法向冲击极为敏感,攻角高于45°后,WC-Co-Cr涂层的冲蚀率为基材的1.3～4.1倍。     

A Study of the Corrosion Resistance of Pump–Compressor Pipes with a Diffusion Zinc Coating under the Complicated Conditions of Gas-Producing Wells

The results of corrosion tests of diffusion zinc coatings under the complicated corrosion and erosion conditions of gas-production wells are presented. The slowdown of the anodic process of the solution of a coating and its salt passivation in model solutions was shown by the electrochemical research. It was established that the corrosion rates of diffusion zinc-coated 36G2F steel samples were 4.1–6.1 times lower than those of samples without coating. The corrosion resistance and the operational reliability of pump–compressor pipes can be increased by using protective duplex system combining a diffuse zinc coating (protective layer) and an upper layer of a polymer coating (barrier layer).     

Plasma Sprayed Coatings of High-Purity Ceramics for Semiconductor and Flat-Panel-Display Production Equipment

High-purity oxide ceramic powders of alumina (Al₂O₃) and yttria (Y₂O₃) have been developed to apply to semiconductor and flat-panel-display (FPD) production equipment. The ceramic coatings on the inside chamber wall of the equipment are required to have high erosion resistance against CFx plasma in dry etching process for microfabrications of the devices. It is found that the yttria coating formed from agglomerated-and-sintered powder consisting of large primary particles has smoother eroded surface with high erosion resistance. Considering the particle deposition on the devices, this coating will be effective in decreasing generation of large-sized particles, which easily deposit on the devices. Electric insulating properties of the coatings are also investigated to apply to electrostatic chuck. Electric breakdown voltage of yttria coatings is comparable to that of alumina coatings. Smaller powder is effective for improving the electric properties, and the influence of coating purity is lower than that of the powder size.     

Prevention of hillock formation during micro-machining of silicon by using OTS-SAM and SiO2 coatings

The feasibility of using a dual coating system consisting of SiO₂ and OTS-SAM thin films on the micro-machining characteristics of silicon wafer were investigated with the aim to eliminate the formation of undesirable hillocks. The outermost OTS-SAM coating was used as a sacrificial layer to pattern the SiO₂ film, which in turn served to pattern the silicon substrate. After selectively removing the OTS-SAM coating by micro-machining, HF and KOH chemical etching processes followed to remove the SiO₂ layer and create patterns on the silicon substrate. By this process, groove patterns of about 1 μm width could be successfully fabricated on a silicon wafer without the formation of undesirable hillocks.     

紫铜表面激光熔覆镍基合金的组织与性能

利用激光熔覆技术在紫铜表面制备镍基合金涂层。采用SEM、XRD、EDS、显微维氏硬度计进行组织结构和硬度分析,并测试了紫铜基体、镍基熔覆层的耐冲蚀磨损性能。结果表明:激光熔覆层与铜基体形成冶金结合,组织致密、晶粒细小、无裂纹、孔隙、夹杂等缺陷,熔覆层内具有等轴晶、树枝晶及平面晶等不同结构,并有Cr、Ni、B等强化相颗粒。当冲蚀角为60°时紫铜基体和熔覆层的质量损失率都比较大,随着冲蚀时间的增加,熔覆层质量损失率比紫铜的质量损失率要低得多,激光熔覆层的耐磨性比基体组织的耐磨性提高了近3倍,激光熔覆层的耐冲蚀磨损性能得到明显提高。     

新型达克罗涂层的制备与组织结构

目的 制备环保的无铬达克罗涂层,研究涂层烧结和腐蚀前后微观组织结构的变化,探究涂层的防腐机制。方法 用锌铝合金粉替代锌铝混合粉,钼酸盐和硅烷偶联剂取代铬酸盐制备无铬达克罗涂料,采用喷涂技术在Q235钢基体上涂装制备涂层。通过X射线衍射仪(XRD)分析涂层在烧结和腐蚀前后的物相组成。通过扫描电子显微镜(SEM)和能谱仪(EDS)分析涂层在烧结和腐蚀前后微观组织形貌的变化。结果 钢基体上无铬达克罗涂层组织致密,表面平滑,呈银灰色,无明显孔隙,涂层厚度为8~12 μm。涂层烧结前后表面均由富锌α相、富铝η相和Fe相组成,但烧结后物相的结晶程度较高,未有新相产生。涂层与基体结合紧密在于涂层中的Zn和Al与基体中的Fe在结合界面处相互扩散形成冶金结合。在浸泡试验中,锌铝合金粉优先溶解为海绵状组织,随后与腐蚀介质反应生成针状成岛状分布的腐蚀产物,腐蚀产物包括Zn5(OH)8Cl.H2O、Al5Cl3(OH)12.4H2O、Zn5(OH)6(CO3)2和少量Fe(OH)3。结论 烧结有利于提高涂层物相的结晶度和涂层表面的致密性,有效发挥涂层物理屏蔽作用。涂层腐蚀防护机制为:腐蚀初期主要发挥片状锌铝粉片层状结构的物理屏蔽作用和腐蚀产物填充涂层破坏区域的自修复作用,随着腐蚀时间的延长,涂层发挥牺牲阳极的阴极保护作用。     

面向铝基发动机气门座圈的激光熔覆铜基合金工艺及性能研究

目的 为了提升发动机气门座圈耐磨耐冲蚀性能,延长发动机寿命。方法 针对铝基发动机气门座圈,采用激光熔覆制备铜基合金覆层,对激光熔覆工艺与熔覆层性能之间的关系进行研究。以稀释率、覆层接触角为衡量标准优化参数,研究激光扫描速度、送粉率、激光重熔参数与熔覆层组织形貌的关系。结果 熔覆层的表层组织随扫描速度的增加而细化,同时,熔覆层的稀释率和覆层接触角均增大,而熔覆层的稀释率和覆层接触角随送粉率的增加呈下降趋势。通过改变激光重熔参数,可改变强化相在熔覆层中的分布情况,从而改变熔覆层硬度。通过对剪切断面进行分析,结果表明,结合界面的剪切强度随着扫描速度的增加先增加后降低,在扫描速度为8 mm/s时,剪切强度最大,为142.31 MPa。在最优参数下,熔覆层的平均硬度为392HV0.05,相当于ZL104铝合金基体硬度(约85HV0.05)的4.6倍。结论 熔覆层冲蚀磨损和销盘磨损试验表明,铜基涂层具有最低的摩擦因数和最低的冲蚀质量损失,印证了铜基覆层可以提升发动机气门原材料的耐磨耐冲蚀性能,并在一定程度上提升发动机缸体寿命,为实际应用提供一定的指导。     

NiCrBSiWCe合金粉末喷熔层滑动磨损特性研究

采用热喷熔方法在45钢表面制备了NiCrBSiWCe合金粉末喷熔层,在SRV磨损试验机上进行小振幅滑动磨损试验研究.结果表明,NiCrBSiWCe合金喷熔层的摩擦磨损性能明显高于SAE52100钢.在较低载荷和滑动速度较低下,小振幅滑动磨损机理为磨损表面的划痕、裂纹和疲劳脱层.而在较高滑动速度下,小振幅滑动磨损机理为磨损表面的氧化磨屑层的形成,含稀土的磨屑层阻碍了喷熔层小振幅滑动磨损.     

Improvement of erosion resistance of titanium with different surface treatments

To improve the erosion resistance of titanium, several surface treatment methods were applied: (1) duplex treatment with carbon nitride film deposited on a plasma-nitrided layer, (2) diamond coating, and (3) laser alloying. Duplex treatment could improve the erosion resistance of titanium under a low impact velocity of erosion particles. However, under a high velocity of erosion particles, because of the shallow depth of the plasma-nitrided layer and low load-bearing capacity of carbon nitride layer on the plasma-nitrided specimen, the improvement of erosion resistance was not significant. Diamond coatings with a thickness of 15 μm made no significant improvement on the erosion resistance of the titanium substrate. The large-area spallation of diamond coating during erosion was observed, probably due to the high residual stresses, poor load-bearing capacity, and brittle nature of diamond coatings. Compared with untreated Ti substrate, the erosion resistance of the laser-alloyed (nitrided) specimen was improved significantly. The erosion mechanisms for laser-nitrided titanium were characterized by chipping, brittle fracture, and formation of large flakes in the laser-nitrided layers.     

Ti6Al4V合金表面火焰喷焊W_xC涂层耐磨性分析

采用"一步法"火焰喷焊技术在Ti6Al4V合金表面制备出由Ni60过渡层和W_xC+Ni60强化层组成的喷焊层。喷焊层在氩气气氛中冷却,避免了涂层的氧化。过渡层与基体结合良好,没有孔洞等缺陷;强化层中碳化钨颗粒呈弥散分布,与过渡层界面处存在大量的孔洞。喷焊层硬度为12. 3 GPa,相比基材,硬度提高了近3倍,摩擦系数降低60%以上。喷焊层与GCr15和Si_3N_4对磨后,对磨副GCr15和Si_3N_4磨损严重,而喷焊层无明显磨损,表现出优异的耐磨性。     

CoCrWSi涂层高温冲击磨粒磨损行为*

CoCrWSi涂层由于其优异的耐高温氧化性能,有望成为汽轮机零部件的防护涂层之一。但是关于该涂层在汽轮机真实服役环境中的高温冲击磨粒磨损行为却鲜有报道。以汽轮机阀门部件材料SA-182F92为基体,制备CoCrWSi防护涂层。利用自研的高温沙粒冲击试验机,研究CoCrWSi涂层在沙蚀环境中的高温冲击磨损行为,通过冲击动力学响应和磨痕形貌来评价该涂层的耐冲击磨粒磨损性能。结果表明：CoCrWSi涂层具有耐高温冲击磨粒磨损性能,具体表现为相同冲击次数下,CoCrWSi涂层样品的磨损面积、磨损体积和最大磨痕深度比基体样品小数倍,CoCrWSi涂层样品的能量吸收量和吸收率均小于基体样品。在高温沙粒环境下,冲击的过程中会有大量的沙粒嵌入磨痕表面,沙粒具有的不规则棱角会切削磨痕表面,进而磨痕表面可以观察到大量犁沟。在高温沙粒环境下,基体与涂层的磨损机理为塑性变形和磨粒磨损。不同的是,软化的基体在冲击区域边缘有明显的隆起,发生更严重的塑性变形;而涂层在冲击过程中虽没有完全剥落,但涂层内部萌生了微裂纹,磨痕表面也有部分涂层剥落。研究结果是在模拟汽轮机真实服役状况下得出的,试验参数如加热温度、沙粒（杂质...     

Adhesion improvements of Thermal Barrier Coatings with HVOF thermally sprayed bond coats

Thermal barrier coatings (TBC) are an effective engineering solution for the improvement of in service performance of gas turbines and diesel engine components. The quality and further performance of TBC, likewise all thermally sprayed coatings or any other kind of coating, is strongly dependent on the adhesion between the coating and the substrate as well as the adhesion (or cohesion) between the metallic bond coat and the ceramic top coat layer. The debonding of the ceramic layer or of the bond coat layer will lead to the collapse of the overall thermal barrier system. Though several possible problems can occur in coating application as residual stresses, local or net defects (like pores and cracks), one could say that a satisfactory adhesion is the first and intrinsic need for a good coating. The coating adhesion is also dependent on the pair substrate-coating materials, substrate cleaning and blasting, coating application process, coating application parameters and environmental conditions. In this work, the general characteristics and adhesion properties of thermal barrier coatings (TBCs) having bond coats applied using High Velocity Oxygen Fuel (HVOF) thermal spraying and plasma sprayed ceramic top coats are studied. By using HVOF technique to apply the bond coats, high adherence and high corrosion resistance are expected. Furthermore, due to the characteristics of the spraying process, compressive stresses should be induced to the substrate. The compressive stresses are opposed to the tensile stresses that are typical of coatings applied by plasma spraying and eventually cause delamination of the coating in operational conditions. The evaluation of properties includes the studies of morphology, microstructure, microhardness and adhesive/cohesive resistance. From the obtained results it can be said that the main failure location is in the bond coat/ceramic interface corresponding to the lowest adhesion values.