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.     

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.     

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.     

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.     

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.     

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...     

Jetting-Out Phenomenon Associated with Bonding of Warm-Sprayed Titanium Particles onto Steel Substrate

Titanium powder particles accelerated and simultaneously heated by the supersonic gas flow were deposited onto steel substrate by the warm spraying process. The sprayed particles were heavily deformed and bonded to the substrate in solid state. Especially, all the deposited particles showed jetting-out of materials out of the particle-substrate interface triggered by the adiabatic shear instability known to occur under such shock impact conditions. High-magnified images showed that grain refinement occurred in the jetting-out region by dynamic recrystallization. Furthermore, the elemental analysis using the electron energy loss spectrum showed jetting-outs of the substrate as well as the particle. Numerical simulation based on the Johnson-Cook plastic deformation model showed that the jetting-out phenomenon commences about 10 ns after the initial contact of the particle with the substrate and at a position away from the center bottom of particle, where the highest compressive stress is experienced.     

Effect of Spray Angle on Temperature Distribution within the Metallic Substrate in Cold Spraying

This study investigates the effect of spray angle on the temperature distribution within the metallic substrate in cold spraying. Computational fluid dynamic approach is employed in this work to achieve this objective. The simulated results show that spray angle significantly influences the temperature distribution within the substrate. For the perpendicular spraying, the temperature gradient contours present regularly annular shape, which means the temperature distribution is only dependent on the radial position. Furthermore, the peak value of the surface temperature is not at the geometric center (stagnation point) but at the position slight away from the center, which may result from the transition of the flow from laminar to turbulent state. Along the radial direction, there exists a secondary peak of the temperature arising from the expansion waves in the adherence jet. With decreasing the spray angle, the secondary peak in the uphill direction disappears. But in the downhill direction, the secondary peak still exits and the distance from the geometric center increases with the decrease in spray angle. In addition, the temperature distribution within the substrate indicates that the residual tensile stress inside the substrate mainly exists near the front zone, but for the angular spraying at the uphill direction, it appears near the back surface. Besides, the simulated results indicate that the best way to preheat the substrate at the angular condition is to move the nozzle from uphill toward the downhill direction.     

0Cr18Ni11Nb表面冷喷涂Cu-Cu_2O涂层的电化学行为研究

采用冷喷涂技术在0Cr18Ni11Nb材料表面制备Cu-Cu2O涂层,研究了其电化学性能。结果表明,随着Cu2O含量的增加,涂层在电解液中的开路电位和腐蚀电位均正移。随着电解液浓度的增加,开路电位先缓慢负移后快速负移,腐蚀电位缓慢负移。     

Numerical Investigation on Effects of Interactions Between Particles on Coating Formation in Cold Spraying

In this study, an investigation on the effects of interactions between copper particles on coating formation was conducted by using a finite element analysis method to clarify the bonding mechanism in cold spraying. The predicted results reveal that the interactions between particles significantly affect the particle deformation and thus coating formation. When the initial parallel distance between particles is short, particles compress with the generation of gap between them. For the vertical case, the initial distance between particles also has an important effect. Short vertical distance makes the subsequent incident particle deform so weakly that the bonding performance is probably not strong enough to form a coating. Furthermore, for successive impacting particles, the subsequent incident particles will tamp the former deposited particles, causing the coating to be little porous near the surface and denser inside the coating.     

Cold Spray Deposition of Copper Electrodes on Silicon and Glass Substrates

Copper lines with widths varying from 150 to 1500 μm were deposited onto crystalline silicon wafers and soda-lime glass plates by cold spraying copper particles with 1 μm average diameter through a mask. This direct deposition method yielded high-aspect-ratio electrodes with minimum shadowing effects and maximum electrode-to-silicon contact area. The copper lines had triangular cross sections with aspect ratios (height/width) ranging from 0.1 to 1.1, depending on the number of spray gun passes. Copper particles were densely packed with increasing the width of the masking slit. This study presents the potential use of the cold spray technology in printing lines as front electrodes in solar cell applications.     

Modeling Aspects of High Velocity Impact of Particles in Cold Spraying by Explicit Finite Element Analysis

In this study, an examination of cold spray particle impacting behavior using the ABAQUS/Explicit program was conducted for typical copper material (OFHC). Various combinations of calculation settings concerning element type, Arbitrary Lagrangian Eulerian adaptive meshing, contact interaction, material damage, etc., were examined with the main focus on the element excessive distortion and its effect on the resultant output. The effect of meshing size on the impact behavior was also clarified compared to the previous results obtained by using the LS-DYNA code. Some fundamental aspects on modeling of cold spray particle deformation are discussed.