Impacting Behavior of Large Oxidized Copper Particles in Cold Spraying

In a previous study, it has been experimentally demonstrated that surface oxide films of metallic particles have significant influence on the properties of cold-sprayed coatings. To clearly reveal the underlying mechanism, this study focused further on the effect of particle oxidation on the deposition behavior of oxidized Cu powder. Results show that the presence of the oxide films on the particles’ surface can inhibit the plastic deformation of the particles. In addition, results concerning the morphologies and oxygen content of the rebounded particles show that the particles have experienced large plastic deformation that results in the break-up of the oxide films during the impacting process. Correspondingly, the hardness of the coating deposited with the oxidized powder is a little lower than that with the annealed powder because of the inferior plastic deformation and strain-hardening effect.     

Effect of Substrate Temperature on Deposition Behavior of Copper Particles on Substrate Surfaces in the Cold Spray Process

The deposition behavior of sprayed individual metallic particles on the substrate surface in the cold spray process was fundamentally investigated. As a preliminary experiment, pure copper (Cu) particles were sprayed on mirror-polished stainless steel and aluminum (Al) alloy substrate surfaces. Process parameters that changed systematically were particle diameter, working gas, gas pressure, gas temperature, and substrate temperature, and the effect of these parameters on the flattening or adhesive behavior of an individual particle was precisely investigated. Deposition ratio on the substrate surface was also evaluated using these parameters. From the results obtained, it was quite noticeable that the higher substrate temperature brought about a higher deposition rate of Cu particles, even under the condition where particles were kept at room temperature. This tendency was promoted more effectively using helium instead of air or nitrogen as a working gas. Both higher velocity and temperature of the particles sprayed are the necessary conditions for the higher deposition ratio in the cold spraying. However, instead of particle heating, substrate heating may bring about the equivalent effect for particle deposition. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Effects of Binder Phase Content and Substrate Hardness on Deposition Behavior of Cermet Particles in Cold Spraying Process

In this paper,three kinds of cermet particles with different binder phase and content,namely WC-12Co,WC-17Co and Cr3C2-25NiCr were deposited on the Q235 low carbon steel and WC-12Co coating substrates to investigate the effect of binder phase content and substrate hardness on deposition behavior of cermet particle during cold spraying.The morphology of the deposited particles was examined by scanning electron microscopy(SEM)from the particle surface and cross-sections.It was found that with increasing substrate hardness,the deposition behavior of cermet particles transformed from completely embedding into substrate to partially flattening and even rebounding.Varying the Co content from 12 wt%to 17 wt% influenced significantly the deposition deformation behavior of the WC-Co particles,the higher Co content brought about a fuller flattening of WC-Co particles.However,Cr3C2-25NiCr particle exhibited the relatively lower flattening ratio and significant rebounding of Cr3C2 even with the highest binder phase content,which may be attributed to the bigger Cr3C2 size and weak bonding between Cr3C2 and NiCr.     

基体表面粗糙度对HVOF粒子沉积行为的影响

目的 研究超音速火焰喷涂时,45#碳钢基体表面粗糙度对WC-12Co粒子在其表面的沉积变形行为的影响.方法 基于Johnson-Cook塑性材料模型与Thermal Isotropy-Phase-Change热材料模型,采用LS-DYNA进行建模分析.结果 不同45#碳钢基体表面粗糙度下,WC-12Co粒子的沉积行为存...     

真空冷喷涂铜颗粒加速特性数值研究

基于Fluent气固两相流数值模拟,研究真空冷喷涂铜颗粒的加速特性,分析了环境压力、喷涂距离、入口总温和颗粒粒径等参数对真空环境下颗粒撞击速度的影响。结果表明:环境压力是决定颗粒撞击速度的关键因素,随环境压力的变化,小直径颗粒(dp≤1μm)撞击速度的变化曲线呈抛物线状态,但大直径颗粒无显著变化;采用合适的喷涂距离,才能获得最大的颗粒撞击速度;增加入口总温可提高小直径颗粒的撞击速度,但对大直径颗粒无明显加速效果;真空冷喷涂颗粒的尺寸可从微米级减小至亚微米级,但过小的颗粒仍难达到足够高的撞击速度。     

Analysis of Bonding Features between the Particles and the Substrate during Cold Spraying

Cold spraying is a new coating process and manufacturing technology. The coating quality is upgraded with dense layers, higher bonding force and lower oxidation comparing with thermal spraying. Bonding of particles onto substrate is a result of extensive plastic deformation and related phenomena at the interface. The cold-sprayed copper and aluminum deposits on aluminum and steel substrates were prepared, and the features of interface were observed by using scanning electron microscope (SEM). Then the particle/substrate impact process was modeling through finite-element methods (ANSYS/LS-DYNA software). Numerical results show that the high plastic strain at the interface can result in an adiabatic shear instability at the interface. Due to these extremely high pressure and strain rate, it may be more appropriate to treat the material adjacent to the particle/substrate interface as a viscous ‘fluid-like’ material, various fluid-based phenomena, such as interfacial instabilities and roll-ups and vortices, can lead to interface material mixing. In numerical simulation, adiabatic shear instability both in the particle and the substrate at contact interface is regarded as a criterion for predicting the optimal process parameters and the bonding feature.     

电爆喷涂粒子的约束调控机制及对沉积行为的影响

采用对喷涂粒子进行槽内约束的电爆喷涂方法,研究了喷涂粒子在垂直槽中的约束调控机制及其沉积行为。结果表明:约束深度达20mm时,即喷涂距离为丝径的100倍时,仍可获得连续、均匀的涂层。约束宽度从6mm减小至2 mm,涂层表面呈现出由粗糙的"丘壑状"形貌向均匀的"薄饼状"形貌逐渐过渡的演变趋势,且涂层厚度显著提高;能量密度从57 J/mm~3提高至152 J/mm~3,同样可提高涂层厚度并改善涂层均匀性。对喷涂粒子进行收集,发现减小约束宽度和提高能量密度均可有效细化喷涂粒子并使喷涂粒子粒径分布更加均匀。分析认为,由焦耳加热导致的"热膨胀效应"和击穿电弧伴生的"压力效应"共同决定电爆冲击波和喷涂粒子的形成,并随能量密度和约束参数的变化,对喷涂粒子表现出不同的约束调控作用,使其沉积行为产生显著差异。     

Study of Substrate Preheating on Flattening Behavior of Thermal-Sprayed Copper Particles

In this study, the effect of substrate preheating on flattening behavior of thermal-sprayed particles was systematically investigated. A part of mirror-polished AISI304 substrates were preheated to 573 and 773 K for 10 min, and then exposed to an air atmosphere for different durations of up to 48 h, respectively. Contact angle of water droplet was measured on the substrate under designated conditions. It was found that the contact angle increased gradually with the increase of substrate duration after preheating. Moreover, smaller contact angle was maintained on the substrate with higher preheating temperature. Commercially available Cu powders were thermally sprayed onto the substrates with the same thermal treatment history as contact angle measurement using atmospheric plasma-spray technique. The splat shape had a transitional changing tendency from a splash splat to a disk one on the substrate with a short duration after preheating, while reappearance of splash splat with the increase of duration was confirmed. In general, wetting of substrate surface by molten particles may dominate the flattening behavior of thermal-sprayed particles. The occurrence of desorption of adsorbed gas/condensation caused by substrate preheating likely provides good wetting. On the other hand, the poor wetting may be attributed to the re-adsorption of gas/condensation on the substrate surface with the increase of duration. In addition, the shear adhesion strength of coating fabricated on blasted AISI304 substrate was enhanced on the once-heated substrate, but weakened with the increase of duration. The changing tendency of the coating adhesion strength and the wetting of substrate by droplet corresponded quite well with each other.     

Deposition Behavior of Semi-Molten Spray Particles During Flame Spraying of Porous Metal Alloy

Porous 316L stainless steel deposits were fabricated by flame spraying semi-molten particles with different melting degrees and spray angles to understand the deposition behavior of semi-molten spray particles. The effects of spray angle relative on the deposition efficiency and deposit porosity were investigated. The morphology of individual splats deposited on flat surface at different angles was examined. The results show that the spray angle had a significant influence on the deposit porosity, pore structure, and deposition efficiency. The slipping of solid core in semi-molten spray particle was clearly observed when semi-molten particles impacted on the polished substrate with an inclined angle. A random model was proposed to simulate the process of particle deposition. It was found that after considering the effects of both solid particle slipping upon impact and particle melting degree, the porosity calculated by simulation with the model agreed well with the experimental observation.     

Finite Element Simulation of Impacting Behavior of Particles in Cold Spraying by Eulerian Approach

In this study, an investigation on the impacting behavior of cold-sprayed particles using the Eulerian formulation available in ABAQUS/Explicit was conducted with typical copper material. The results show that a jet cannot be formed at an impact velocity less than about 290?m/s, while a continuous jet composed of both particle and substrate materials begins to initially form at about 290?m/s and a maximum equivalent plastic strain plateau can be found, which could be the approximate critical velocity. In addition, the jet presents discontinuities and the splashing causes the loss of material as the impact velocity exceeds the velocity extent of 290-400?m/s. Therefore, through theoretical analysis of the jet morphology, the Eulerian model could provide a prediction of the critical velocity.     

Effects of Substrate Hardness and Spray Angle on the Deposition Behavior of Cold-Sprayed Ti Particles

In this study, finite element analysis combined with experimental observation was conducted to clarify the effects of substrate hardness and spray angle on the deposition behavior of cold-sprayed Ti particles. It is found that metallurgical bonding is highly possible to occur between the Ti particle and Cu substrate due to the intensive metal jet at the rim of the interface which helps to remove the cracked oxides. Because metallurgical bonding and large interfacial contact area can guarantee high adhesion strength, the thick Ti coating is achieved after deposition on the Cu substrate. As for the soft Al substrate, the first layer Ti particles are embedded in and then trapped by the soft substrate material, which results in the occurrence of mechanical interlock at the interface. As a consequence, the final coating thickness is also relatively large. When using hard stainless steel as the substrate, the essential conditions for forming the mechanical interlock are lacked due to the high hardness of the substrate material. In addition, the metal jet at rim of the interface is less prominent and also the interfacial contact area is smaller in comparison with the Ti-Cu case. Therefore, the particle-substrate bonding strength and the consequent coating thickness are relatively low. Besides, it is also found that the particle deformation and coating quality are significantly affected by the spray angle. The deformation of the particle localizes at only one side due to the additional tangential momentum. Also, such localized deformation becomes increasingly intensive with decreasing the spray angle. Moreover, the coating thickness is found to reduce with the decrease in spay angle, but the coating porosity shows a reverse trend.     

Multiscale Model on Deposition Behavior of Agglomerate Metal Particles in a Low-Temperature High-Velocity Air Fuel Spraying Process

A multiscale model was constructed for agglomerate metal particle deposition in a low-temperature high-velocity air fuel (LTHVAF) thermal spraying process using finite element analysis (FEA) and smoothed particle hydrodynamics (SPH). Here, the agglomerate particle impact on the substrate is simplified to three states. Then, the corresponding model is selected. The simulated results show that the temperature and velocity of agglomerate particle can affect the effective temperature and plastic strain in the contact interface for increasing particle energy. At the microscale, the deformation of the deposited particle might coarsen the coating surface to the extent that the critical velocity of the metal particle would decrease. It indicates that the agglomerate particle might splash when it impacts on the substrate. The transient melting can be ascertained at an angle in an approach to the achievement of intermetallics combined with the modeling of the particle penetrating into the substrate. In this process, the effective strain of an agglomerate particle at the nanoscale is less than that at microscale, but the surface area ratio at nanoscale is large. The uncompacted state of the agglomerate particle can lead to a turbulent force when the agglomerate particle deposits on the substrate, which can reduce the penetration performance of the particle. This behavior can decrease the stress-strain of substrate and cause the cracked particle to sparkle.     

Cold Gas-Sprayed Deposition of Metallic Coatings onto Ceramic Substrates Using Laser Surface Texturing Pre-treatment

Cold spraying enables a variety of metals dense coatings onto metal surfaces. Supersonic gas jet accelerates particles which undergo with the substrate plastic deformation. Different bonding mechanisms can be created depending on the materials. The particle–substrate contact time, contact temperature and contact area upon impact are the parameters influencing physicochemical and mechanical bonds. The resultant bonding arose from plastic deformation of the particle and substrate and temperature increasing at the interface. The objective was to create specific topography to enable metallic particle adhesion onto ceramic substrates. Ceramic did not demonstrate deformation during the impact which minimized the intimate bonds. Laser surface texturing was hence used as prior surface treatment to create specific topography and to enable mechanical anchoring. Particle compressive states were necessary to build up coating. The coating deposition efficiency and adhesion strength were evaluated. Textured surface is required to obtain strong adhesion of metallic coatings onto ceramic substrates. Consequently, cold spray coating parameters depend on the target material and a methodology was established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Laser surface texturing is a promising tool to increase the cold spraying applications.     

冷喷涂粒子碰撞行为和临界速度预测的数值模拟研究现状

目前,冷喷涂技术受到越来越多国内外学者的关注。文中基于已公开发表的文献,详细讨论了冷喷涂过程中粒子碰撞行为的数值模拟和临界速度预测的研究现状。首先,简要介绍了冷喷涂、粒子结合机理和临界速度的概念。其次,总结了拉格朗日法、欧拉法和光滑粒子法等数值计算方法,并对数值计算获得的结果,例如:变形形貌、界面温度、能量变化及临界速度的预测进行了讨论。最后,探讨了冷喷涂粒子碰撞行为数值模拟中存在的问题和研究前景。     

Examination on Substrate Preheating Process in Cold Gas Dynamic Spraying

Substrate preheating always takes an important role in particle bonding and formation of the first layer coating in cold gas dynamic spraying (CGDS). In this study, a systemic investigation on substrate preheating process is conducted with Cu, Al, Steel, and Ti substrate by both numerical and experimental methods. The computational fluid dynamic (CFD) approach is adopted to simulate the heat exchange process between gas and solid substrate. The numerical results show that substrate can be significantly preheated by the high-temperature gas, especially by the gas at the near-wall zone behind the bow shock where the temperature is extremely high. Moreover, the comparison between different substrates implies that substrates with smaller thermal conductivity can achieve higher surface temperature and larger temperature gradient which may greatly contribute to the generation of residual stress, such as Ti substrate in this study. For the heat flux, Cu substrate obtains the largest value at the center zone of the substrate surface, followed by Al, Steel, and Ti substrate, but at the outer zone, the heat flux through the Cu substrate surface is smaller than the other three types of substrates. Besides, based on the experimental results, it is found that the substrate surface temperature amounts to the peak value only when the preheating time is sufficiently long.     

Microstructural Development and Deposition Behavior of Titanium Powder Particles in Warm Spraying Process: From Single Splat to Coating

Warm spraying has been developed by NIMS, in which powder particles are accelerated and simultaneously heated, and deposited onto a suitable substrate in thermally softened solid state. In this study, commercially available titanium powder was sprayed onto steel substrate by the spraying process. Microstructural developments and deposition behaviors from a deposited single particle to a thick coating layer were observed by high resolution electron microscopes. A single titanium particle sprayed onto the substrate was severely deformed and grain-refined mainly along the interfacial boundary of particle/substrate by the impact of the sprayed particle. A successive impact by another particle further deformed the previously deposited particle and induced additional grain refinement of the remaining part. In a thick coating layer, the severe deformation and grain refinement were also observed. The results have demonstrated the complex deposition behavior of sprayed particles in the warm spraying using thermally softened metallic powder particles.     

Corrosion Resistance of Copper Coatings Deposited by Cold Spraying

In the article, a study of corrosion resistance of copper and copper-based cermet (Cu+Al₂O₃ and Cu+SiC) coatings deposited onto aluminum alloy substrate using the low-pressure cold spraying method is presented. The samples were subjected to two different corrosion tests at room temperature: (1) Kesternich test and (2) a cyclic salt spray test. The selected tests were allowed to simulate service conditions typical for urban, industrial and marine environment. Examination of corroded samples included analysis changes on the coating surface and in the microstructure. The physicochemical tests were carried out using x-ray diffraction to define corrosion products. Moreover, microhardness and electrical conductivity measurements were conducted to estimate mechanical and physical properties of the coatings after corrosion tests. XRD analysis clearly showed that regardless of corrosion conditions, for all samples cuprite (Cu₂O) was the main product. However, in the case of Cu+Al₂O₃ cermet coating, chlorine- and sulfate-containing phases such as Cu₂Cl(OH)₃ (paracetamite) and Cu₃(SO₄)(OH)₄ (antlerite) were also recorded. This observation gives better understanding of the lowest microstructure changes observed for Cu+Al₂O₃ coating after the corrosion tests. This is also a justification for the lowest decrease in electrical conductivity registered after the corrosion tests for this coating.     

乙醇体系中铜基材浸镀银的动力学研究

以硝酸银为主盐,乙二胺为络合剂,乙醇为溶剂,在紫铜表面镀银。研究了浸镀银平均沉积速率随时间的变化规律,并对沉积速率与银离子浓度、乙二胺加入量、镀液温度、镀液pH值和乙醇加入量等工艺参数的关系曲线进行线性拟合,得到了各反应级数和表观活化能。最后得出动力学沉积速率方程,并进行了验证。     

The Effect of Substrate Surface Oxides on the Bonding of NiCr Alloy Particles HVAF Thermally Sprayed onto Aluminum Substrates

The effect of substrate surface oxides on splat-substrate bonding was investigated by thermally spraying NiCr particles onto aluminum substrates with surface oxide layers grown hydrothermally and electrochemically. Cross sections of bonded solid and molten splats revealed substantial deformation of both the substrate and the surface oxide. In spite of the substantial substrate deformation, there was no significant loss of the surface oxide material and there was no observed diffusion of the substrate oxide into the NiCr particle or vice versa. For solid splats, the substrate oxide was still present over the entire splat-substrate interface, however for molten splats, the oxide had been penetrated in several locations allowing close proximity of the splat metal to the substrate metal. These results strengthen the theory that oxide layers impede bonding and that successful bonding occurs only when the surface oxide is substantially deformed or disrupted to produce mechanically interlocking features at the interface.     

铜基材乙醇体系浸镀银工艺的研究

为解决传统水相体系浸镀银所存在的问题,笔者采用乙醇溶液体系,以硝酸银为主盐,乙二胺为络合剂,并就银离子浓度、络合剂与银离子摩尔浓度比以及镀液pH值等工艺参数,对紫铜浸镀银镀层性能的影响进行了研究.试验结果表明:当银离子质量浓度为2.0 g/L,络合剂与银离子摩尔浓度比为4∶1,镀液pH值为9.8,温度为室温时,可以在紫...