等离子喷涂-物理气相沉积的气相沉积机理

以等离子喷涂-物理气相沉积(PS-PVD)喷涂团聚的 ZrO₂-7wt%Y₂O₃(7YSZ)粉末在五个喷距下制备了热障涂层。通过场发射-扫描电镜(FE-SEM)和X射线衍射(XRD)分析了五个涂层样品的微观结构和相成分差异。另外, 通过发射光谱(OES)诊断研究了射流中7YSZ粉末气相浓度随喷距的变化。最后, 阐述了3种不同的气相沉积涂层生长机制, 说明了射流中粉末的状态和气相浓度对涂层结构的影响。研究表明：(1)350 mm和1800 mm喷距下形成的均是致密结构涂层, 而650~1250 mm喷距下形成的是典型的PS-PVD柱状结构涂层。(2)350 mm喷距下制备的涂层由四方相(t’)和单斜相(m)氧化锆构成; 当喷距大于650 mm时, 涂层以四方相(t’)氧化锆为主。(3)350 mm喷距下涂层是由高浓度气相过饱和自发形核形成的新核和液/固粒子共同作用形成的; 喷距650~1250 mm下, 涂层生长以气相沉积于基体进行非自发形核为主, 气相在射流中的自发形核为辅; 喷距1800 mm下涂层由气相过冷凝固的粒子堆积而成。     

粘结层喷涂方法对铜基体与热障涂层结合强度的影响

为提高铜基体上热障涂层的工作温度和寿命,分别采用超音速火焰喷涂(HVOF)和等离子喷涂(APS)制备NiCrAlY粘结层,采用等离子喷涂制备ZrO2-8%Y2O3陶瓷面层.用拉伸试验测试了热障涂层的结合强度,利用SEM分析了拉伸断口的成分分布和微观形貌.研究表明,用HVOF制备粘结层的热障涂层的结合强度为47.9 MPa,用APS制备粘结层的热障涂层的结合强度为31.2 MPa.与等离子喷涂制备粘结层相比,采用超音速火焰喷涂制备粘结层可明显提高ZrO2陶瓷涂层的结合强度.     

Formation of high heat resistant coatings by using gas tunnel type plasma spraying

Zirconia sprayed coatings are widely used as thermal barrier coatings (TBC) for high temperature protection of metallic structures. However, their use in diesel engine combustion chamber components has the long run durability problems, such as the spallation at the interface between the coating and substrate due to the interface oxidation. Although zirconia coatings have been used in many applications, the interface spallation problem is still waiting to be solved under the critical conditions such as high temperature and high corrosion environment. The gas tunnel type plasma spraying developed by the author can make high quality ceramic coatings such as Al2O3 and ZrO2 coating compared to other plasma spraying method. A high hardness ceramic coating such as Al2O3 coating by the gas tunnel type plasma spraying, were investigated in the previous study. The Vickers hardness of the zirconia (ZrO2) coating increased with decreasing spraying distance, and a higher Vickers hardness of about Hv = 1200 could be obtained at a shorter spraying distance of L = 30 mm. ZrO2 coating formed has a high hardness layer at the surface side, which shows the graded functionality of hardness. In this study, ZrO2 composite coatings (TBCs) with Al2O3 were deposited on SS304 substrates by gas tunnel type plasma spraying. The performance such as the mechanical properties, thermal behavior and high temperature oxidation resistance of the functionally graded TBCs was investigated and discussed. The resultant coating samples with different spraying powders and thickness are compared in their corrosion resistance with coating thickness as variables. Corrosion potential was measured and analyzed corresponding to the microstructure of the coatings. Keywords: High Heat Resistant Coatings, Gas Tunnel Type Plasma Spraying, Hardness,     

Determination of the thickness of metal coatings on granular diamond materials by spatially resolved optical methods

The embedding of surface-modified granulates into metallic matrices is a promising way to optimize the interface matrix/granulate in respect to mechanical and thermal properties. In the case of surface modification by coating, a reliable determination of the coating thickness on granulates is desirable, since the interface properties may depend on it to a critical extent. This paper proposes a simple method to determine the thickness of transparent metal coatings on diamond substrates. Diamond granulates with grain sizes between 100 and 120 μm were coated with molybdenum in an intermixing device which allows reasonable film uniformity on granulates. The deposition method was single source DC magnetron sputtering with argon as working gas. By comparing the transmission of the uncoated and coated diamonds with an optical scanner, the coating thickness could be determined from the known extinction coefficient. A good correlation between the measured film thicknesses and the deposition time was achieved. It can be concluded therefore, that the presented method is a viable and cost-efficient way for the determination of the average thickness of transparent metallic coatings on a sample of transparent granular substrates, with an estimated minimum and maximum measurable thickness of 2.5 nm and 15 nm respectively for molybdenum.     

喷涂距离对Fe基非晶涂层孔隙影响的研究

热喷涂涂层中孔隙的存在会降低涂层的耐蚀性,减少涂层寿命,而热喷涂工艺参数很大程度上影响涂层的孔隙率。本文采用计算机数值模拟和设计验证实验的分析方法,重点研究了JP-8000超音速火焰喷涂系统(HVOF)制备Fe基非晶涂层工艺参数中喷涂距离与涂层孔隙的关联性。利用商用计算软件Fluent计算平台,研究加入粉末粒子前,喷枪内火焰温度和速度的变化规律,以及加入非晶粉末后,不同喷涂距离条件下颗粒飞行过程的温度和速度的变化规律。仿真结果表明,喷涂距离为360~380 mm时,非晶粉末颗粒在撞击基板时处于半融化状态,颗粒在基板上具有良好的流动性,可获得孔隙率较低的涂层。验证实验结果与仿真结果一致。X射线衍射结果表明,粉末、不同喷涂距离所制备的涂层以及同成分的非晶条带均为完全非晶态结构。SEM和孔隙率统计结果表明,喷涂距离为370 mm时,涂层截面的孔隙较少,且孔隙率最低,为0.57%,验证了计算模拟优化的最佳喷涂距离范围。     

Study of the delamination of diamond coatings under thermal stress

The influence of the thickness of CVD diamond coatings on the adhesion to a substrate, after cooling down from deposition temperature to room temperature, has been studied experimentally and theoretically. Diamond layers have been deposited at 850°C on W substrates by microwave plasma enhanced CVD. Cooling down of the substrate-diamond coating system to room temperature induces thermal stresses, due to different thermal expansion coefficients of coating and substrate. For thick diamond coatings a total and sudden delamination could be observed as a consequence of these stresses. On the contrary thin coatings, produced under identical circumstances, adhered well. These phenomena have been modelled and explained by the use of an energetic criterion for the delamination of a two-layer system under thermal stress. From the model a critical thickness of the coating can be calculated. Above this critical thickness, delamination will suddenly occur. The calculations also predict that for intermediate coating thicknesses delamination can easily be induced by external causes.     

High-velocity oxygen fuel spray coatings for reclamation

These coatings are produced by a spray of molten powder in a system which has recently been developed utilizing a high-velocity fuel mixture of oxygen-propylene or oxygen-hydrogen. These gases are ejected at high speed from a nozzle and then ignited externally to form a flame which envelops the spray material. A high-velocity flame of compressed air carries the molten powder to a specially prepared surface where it solidifies to form a very dense coating of high bond strength and low porosity. The composition of the coating can be varied and depends upon that of the powder, the most commonly used for reclamation being based on either iron or nickel or tungsten carbide. During coating, the substrate temperature is held below 423 K so the process is considered ‘cold’. The spray coatings have good adhesion with low porosity. The high hardness and cost competetiveness means that they are beginning to replace electrodeposited nickel and chromium which have long been used for the repair of engineering components.     

低压冷喷涂铝涂层微观结构与沉积特性研究

低压冷喷涂技术是一种不同于高压冷喷涂技术的新型喷涂工艺。本文以体积比为3:7的氧化铝粉末和铝粉的混合粉末为原料,以压缩空气为工作气体,利用低压冷喷涂设备在Q235钢基体上制备Al涂层,研究了温度、喷距、送粉速率和喷嘴横向移动速度等工艺参数对涂层沉积效率的影响。采用光学显微镜、扫描电镜,研究了涂层的微观结构和沉积特性。实验结果表明:在工作气体压力保持0.6 MPa不变的情况下,温度400℃、喷距25 mm、送粉速率为30—40 g/min、喷嘴横向移动速度4.0 m/min时,铝涂层沉积效率最佳;同时Al2O3陶瓷相的加入有利于涂层的沉积。     

A Novel Manufacturing Route for Automobile Parts through Two-Wire-Arc Thermal Spray Process

The present work deals with a novel manufacturing route that can be used to fabricate automobile sheet parts such as bonnet/bumper by metal alloy coating through two-wire-arc thermal spray (TWATS) process. Later the coating is supported with fiber through cladding process and becomes a freestanding composite coating. The coating has a metallic look and is free from oxidation. This novel manufacturing process is rapid and customized. A case study, where aluminum alloy wire was used to produce freestanding coating, was performed by response surface method optimization of the two-wire-arc spray process factors: the voltage, current, spray distance, gas pressure, and selection of mold/substrate material that was used to fabricate automobile bonnet. Initial experiments were performed on the four different substrates materials, viz., steel, aluminum, ceramic, and graphite; the graphite substrate showed some promising results and was selected to run the experimental array to optimize the process parameters. Spray distance more than 150 mm, voltage 30 V, current 250 A, and primary atomizing gas (nitrogen) pressure 100 psi (0.689 MPa) may be used. The freestanding aluminum coating was evaluated analyzing its performance, in terms of desirable microstructure and mechanical properties.     

金属载体催化剂涂层制备技术的研究进展

为解决金属载体催化剂活性涂层涂覆困难且使用过程中易剥落的问题,通过对金属载体进行表面处理得到过渡层／膜,其可以提高后续涂层的结合力。介绍了不同金属载体催化剂涂层的制备技术,讨论了各种方法的优缺点,进而提出了金属栽体涂层技术的发展方向。     

Development,characterization and erosion wear response of plasma sprayed fly ash–aluminum coatings

This paper describes the processing, characterization and the erosion wear response of a new class of metal–ceramic composite coatings deposited on metal substrates by plasma spraying. Coatings are developed on aluminum substrates using fly ash pre-mixed with aluminum powder in different weight proportions at various plasma torch power levels ranging from 9 to 18 kW DC. The coatings are characterized in terms of thickness, interface adhesion strength and deposition efficiency. Maximum adhesion strength of about 35 MPa is recorded with coatings deposited at 12 kW power level. It is noticed that the adhesion strength of fly ash coating is improved with pre-mixing of aluminum up to 15 wt.% in the feed material. To study the erosion wear behavior of the coatings, a plan of experiments based on the Taguchi technique is used to acquire the erosion test data in a controlled way. An orthogonal array and signal-to-noise ratio are employed to investigate the influence of the impingement angle, impact velocity, erodent size, stand-off-distance and the aluminum content in the feed stock on the erosion rate. The study reveals that the impact velocity is the most significant factor influencing the erosion wear rate of these coatings.     

Applikation ausscheidungshärtender Bronzeschichten mittels Hochgeschwindigkeitsflammspritzen

Application of age hardenable‐copper‐based‐coatings trough HVOF‐spraying Thermal spraying of age hardenable copper based alloys, enables the producing of wear resistant coatings with high conductivity. With high velocity flame spraying it is possible to create dense coatings with good adhesion to the substrate. The coatings are produced in two steps the thermal spray process itself and the followed heat treatment. The characterisation of the produced specimen shows promising results. The achieved wear resistance of the coatings is similar to bulk material and better than pure copper.     

Improved adhesion between a sputtered alumina coating and a copper substrate

The influence of various metallic intermediate layers on the adhesion between a copper substrate and an alumina coating was studied. The alumina coatings and the intermediate layers were prepared by r.f. sputtering. Titanium and combined Ni/Ti intermediate layers were used. The adhesion properties of alumina with different combinations of coatings were compared by an interrupted tensile testing method and by thermal cycling from room temperature to 600°C.The adhesion of a sputtered alumina coating to a copper substrate without any intermediate layer appeared to be rather poor. The use of titanium as an intermediate layer enhanced the adhesion significantly. The adhesion was further increased when the deposition temperature of the titanium was increased from 200 to 350°C. The combined Ni/Ti intermediate layer led to better adhesion than the titanium layer alone did.     

超音速冷气体动力喷涂的涂层微结构

超音速冷气体动力喷涂是近年来兴起的一种表面涂层和粉末固结的新技术.本文在自行建造的冷喷涂实验装置上,实现了以氮气为载气的铜粉向铝板的超音速冷喷涂沉积.采用金相显微镜、表面轮廓仪、扫描电子显微镜和x射线衍射仪等对冷喷涂涂层样件的微结构特性进行了分析.结果表明,金属粒子与基板之间高速撞击过程中发生的塑性变形,使其与基板相结合,实现沉积.x射线衍射仪检测结果表明涂层成份基本与粉末成份相同,喷涂前后金属粉末未被氧化.涂层中存在少量的铜-铝合金,证明冷喷涂形成的涂层具有很高的结合强度,甚至在局部可以形成冶金结合.     

Effects of heat treatment on adhesion strength of thermal barrier coating systems

Thermal barrier coatings (TBCs) are widely used as protective and insulative coatings on hot section components of gas turbines and their applications, like blades and combustion chambers. The quality and performance properties of TBCs are of great importance in terms of their resistance to service conditions. In a TBC system, there is a close relationship between the adhesion properties of coating layers. The adhesion strength of TBCs varies depending on the coating technique used and the surface treatments. In this study, CoNiCrAlY and YSZ (ZrO₂ + Y₂O₃) powders were deposited on stainless steel substrate. High Velocity Oxy-Fuel (HVOF) and Atmospheric Plasma Spraying (APS) techniques were used to produce the bond coats. The ceramic top layers on CoNiCrAlY bond coats were produced by the APS technique. The TBC specimens were subjected to heat-treatment tests. Adhesion strength for top coat/bond coat interface of as-sprayed and heat-treated samples was investigated. The results showed that the heat treatment of the coatings in different temperatures led to an increase in the adhesion strength of TBCs.     

A modified blister test to study the adhesion of thin coatings based on local helium ion implantation

A modified blister test has been developed based on helium ion implantation into selected areas of the metal substrate prior to the coating deposition. After a post-deposition thermal annealing, blisters are formed by agglomeration of the implanted gas at the ceramic–metal interface. This method can be used to control the pressure in the blister which eventually may lead to delamination at the periphery of the blister. A microsieve with a regular array of circular holes is used during the implantation to assure the initial blister size. Two different microsieves were employed in this work, with pore diameters of 1.5 and 4.5 μm, respectively. The distance between the centres of neighbour pores is twice the pore diameter. Scanning Electron Microscopy (SEM) and Confocal Scanning Optical Microscopy (CSOM) observations allowed the determination of the blistering parameters such as the radius, the height and the blister volume. From the gas content and these parameters, the work of adhesion or energy release rate can be obtained.In this work, we present the first results of this blister test applied to W–C:H films and multilayers of Ti and Al deposited by Physical Vapour Deposition on polycrystalline copper substrates. The copper substrates were implanted with 34 keV He⁺ ions up to fluences of 3 and 5×10¹⁶ cm⁻² before the deposition of the coatings and annealed afterwards in vacuum at temperatures from 773 to 1073 K for 30 min. Delamination of the Ti/Al multilayer coatings was already detected after annealing at 873 K with an energy release rate estimated to be 0.5 J m⁻² at a typical helium pressure of 10⁷ Pa. No delamination but only helium swelling was observed for W–C:H coatings annealed at 1073 K. Results of experiments on uncoated copper samples are also shown in order to explain the mechanism of helium bubble growth and helium release that causes the creation of the blisters.     

Effects of bias voltage and gas pressure on orientation and microstructure of iridium coating by double glow plasma

Iridium coating was produced on various substrates using a double glow plasma. The effects of bias voltage and gas pressure on orientation and microstructure of the coating were studied. The orientation, microstructure and composition of the coating were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results showed that iridium coatings on various substrates all exhibited the preferred (220) orientation under the same deposition conditions. The microstructure of the coating was affected by bias voltage, gas pressure and substrate effects. The bias voltages had a significant impact on the crystal orientation of the coating. The increase of bias voltage resulted in high substrate temperature and large deposition rate. An increase in the coating thickness can affect the microstructure and orientation of the coating.     

Effects of bias voltage and gas pressure on orientation and microstructure of iridium coating by double glow plasma

Iridium coating was produced on various substrates using a double glow plasma. The effects of bias voltage and gas pressure on orientation and microstructure of the coating were studied. The orientation, microstructure and composition of the coating were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results showed that iridium coatings on various substrates all exhibited the preferred (220) orientation under the same deposition conditions. The microstructure of the coating was affected by bias voltage, gas pressure and substrate effects. The bias voltages had a significant impact on the crystal orientation of the coating. The increase of bias voltage resulted in high substrate temperature and large deposition rate. An increase in the coating thickness can affect the microstructure and orientation of the coating.     

Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer

Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.