In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. There is a rectangular and a circular cross-sectional shapes on the cold spray nozzle. It has been reported that the rectangular nozzle provide a more uniform particle velocity across the exit of the nozzle. The circular exit nozzle is parabolic in shape. So spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle in order to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviours of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. In this study, the spray pattern and microstructure of copper coatings with the rectangular cross-section nozzle optimized by CFD analysis in high-pressure cold spraying are reported. The optimized rectangular nozzle provide a more uniform spray profile of coatings. Relatively finer powder tended to deposit on the end of the coating.

In this work, pure silicon and Ni-P coated silicon powders were cold sprayed on copper foil. To thicken coating layers, 2-pass and 3-pass coatings were carried out. In the case of Ni-P coated silicon powders, coated anodes show excellent charge-discharge characteristics after two passes. For the pure silicon powders, however, even if a 2-pass operation is performed, the additional attached silicon mass is only 2~3 %. This means that multi-pass spraying is not an effective way to increase the thickness of pure silicon coatings produced by cold spraying.

The goal of this work is to establish a design for a cold spray nozzle that produces a flatter spray pattern. To that end, experiments and CFD calculations are carried out to investigate the influence of nozzle geometry and expansion ratio on the behavior of copper particles and gas flows during high-pressure cold spraying. It is found that there is an optimal ratio for the lengths of the diverging and parallel sections in a rectangular nozzle in regard to particle velocity and deposition efficiency. The results are also compared with circular nozzle designs.

Mechanical properties of WC-Co coatings prepared by cold spraying (CS) and warm spraying (WS) have been studied with changing material parameters of Co content (12~25%), powder size (-45+15 and -20+5 µm) and WC particle size (0.2 and 1.8 µm) in this paper. The study reveals that a formation of undesirable phases such as W 2 C, W, and amorphous or nanocrystalline Co-W-C (eta) phase has been suppressed in the CS and WS coatings. Both coatings have high hardness, which is comparable to or superior to HVOF coatings as well as higher density (low porosity) than the HVOF. Abrasion wear test has shown that WS coatings has higher resistance than CS coatings within this study. As for powder properties, smaller powder and smaller WC particle sizes are effective to produce hard and dense coatings leading to higher wear resistance.

Aluminum powder of 99.85 wt.% purity has been sprayed onto three kinds of glass substrates by cold spray. An interface between Aluminum coating and all glass substrates were smooth, and the single aluminum particle adhered without a gap. It is not observed erosion damage of glass substrate by aluminum with lower impact velocity than critical velocity. In Aluminum coating and the neighborhood of interface of Soda-lime glass substrate, sodium included in glass substrate was distributed in high density. There might be the stratum that the element which constituted an aluminum coating and glass substrate scattered, and it was suggested that the solid-phase joining by a chemical reaction were initiated.

In this study, an aluminum coating with dispersed quasicrystalline particles is produced by cold spraying. The spraying was done using helium gas at a temperature of 400 °C. The obtained coating exhibited a relatively precise microstructure with almost no macroscopic voids. X-ray and TEM analyses confirmed that the coating retained its quasicrystal structure on the surface as well as internally. TEM analysis also revealed that metallic bonding occurred at powder-powder and powder-substrate interfaces. Although the hardness of the coating was higher than that of extruded bulk alloy, tensile strength was found to be much lower, which is attributed to defects at particle-particle interfaces.

Nozzle geometry influences gas dynamics, such as gas density, velocity and temperature, making sprayed particle behavior one of the most important parameters in cold spray process. Gas flow at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour (convergent –divergent and convergent-divergent-barrel), entrance geometry of convergent–divergent nozzle and powder injection position at nozzle on the cold spray process. The process changes inside the nozzle were observed through numerical simulation studies and the results were used to find a correlation with coating properties. A copper and titanium powder was used in the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 623K, respectively. In addition, the change in the nozzle contour and the change in the entrance convergent section length of the gun nozzle were found to have a slight effect on the coating microstructure. Powder injection position was also found to influence deposition efficiency and coating properties. Deposition efficiency of both copper and titanium increase with increasing the length of the convergent section of the nozzle.

Wear properties of WC/Co cermet coatings have been investigated prepared by cold spraying. Influence of cobalt contents (12~25wt.%), WC particle size (0.2 and 1.8 µm) and agglomerated-and-sintered powder size (-20+0 and - 45+15 µm) on abrasive wear resistance, micro hardness and coating structure is studied, in detail. It has been found that both smaller WC particle and decrease of cobalt content are effective to produce dense, hard and highly wear resistant coating. Smaller powder size is also favorable to make a coating with high mechanical properties. As a result, the cold sprayed coating from WC(0.2 µm)/12wt.%Co with powder size of -20+0 µm has best mechanical properties within this study. This coating has high uniformity and high density with little pores compared to conventional HVOF sprayed coatings. Abrasive wear resistance of the cold sprayed coating, investigated using Suga-abrasion tester, has been almost comparable to HVOF sprayed coating prepared from same feedstock. Strong correlation is also seen between Vickers hardness and abrasive wear resistance. Microstructural analysis suggests that further improvement of coating uniformity by decrease of small pores with the size of sub micron and homogeneous dispersion of WC grains in the cobalt matrix is required to improve the mechanical properties.

Currently, graphite is used for anodes of the lithium ion battery. The higher capacity of a battery with the lithium alloy anode requires the development of a larger theoretical electrochemical capacity than graphite. Silicon is a promising anode material, having a theoretical capacity more than 10 times that of the graphite used in these lithium alloy batteries. There are two common methods of fabricating silicon anodes: direct deposition techniques such as electron beam deposition and sputtering; and slurry coating of silicon particles with a binder. Alternative methods are being investigated. One of such methods is cold spray. In this study, numerical simulation of, and experiments investigating, cold spray conditions and the performances of cold-sprayed silicon anodes are presented. Silicon was cold-sprayed on copper foil substrates using three different starting materials (with particle sizes of 4.65 µm, 6.74 µm and 9.63 µm). First cycle efficiency was about 90%. Charge capacity initially improves with cycling (up to the 10th cycle). This is probably due to better electrolyte soaking during the first several cycles. A decrease in charge capacity is observed upon further cycling.

Powder size, which influence on spray particle behavior in super sonic gas flow in and out of nozzle, is one of the most important parameters in cold spray process. In the other hands, it was reported that small particles (smaller than 5ƒÊm in diameter) decelerate significantly close to the substrate by the bow shock in cold spray. In this study, numerical simulation and experiments investigated the effect of the powder size of copper on the cold spray process and the structures and properties of the cold sprayed coatings. In the numerical simulation, it is assumed that gas flow within the nozzle is quasi-one-dimensional isentropic flow of semi-perfect gas. A spray powder of copper is used. Mean diameter of copper powder 1, 5, 10, 15 @and 45ƒÊm are used. Working gas (is nitrogen) pressure and temperature at nozzle-intake are 3MPa and 350 ‹C. With decreasing particle diameter, calculated particle velocity at the nozzle exit increase immediately. So deposition efficiency increase immediately with decreasing particle diameter until 5ƒÊm. Abstract only; no full-text paper available.

In this study, experiments investigated the influence of substrate conditions such as substrate thickness, substrate surface conditions (blasted or polished), substrate temperature, number of overlaps and gun traverse speed on cold sprayed copper and titanium coatings. The influence of substrate thickness, substrate temperature and number of overlaps were different by materials of feedstock powder (copper and titanium). In another words, titanium deposition efficiency increase slightly while copper deposition efficiency decrease slightly with increasing the substrate thickness, the preheated substrate temperature and number of overlaps and gun traverse speed. On the other hands, both deposition efficiency of copper and titanium coating increase slightly with an increase in surface roughness from 0.2 μm Ra (polished surface) to 7 μm Ra (blasted surface). The deposition efficiency of titanium and copper decrease rapidly with increasing gun traverse speed.

Cold spray nozzles can have a significant impact on particle behavior and coating quality depending on their shape and size. This study investigates the influence of nozzle geometry on the cold spray process. Simulations show that particle velocities are highest at the outlet of de Laval type nozzles and that convergence pipe nozzles achieve the highest particle temperatures. Paper includes a German-language abstract.

A high-velocity oxyfuel plant was converted to process aluminum oxide. Burner nozzles with different geometries were evaluated for use based on experimental measurements and numeric simulations. Although the modified nozzles promised an improvement in the melting of alumina particles, it was found that some of the melted alumina caked on the inside of the nozzle and fused together into large particles that eventually dislodged, causing a reduction in transfer efficiency. This paper explains how the caking problem was solved by combining the output of a high-velocity oxyfuel gun with that of a combustion flame spraying gun. Tests show that the hybrid solution produces hard alumina coatings with relatively dense microstructure at a transfer efficiency greater than 50%. Paper includes a German-language abstract.

In wire arc spray, atomizing gas is one of the most important parameters. The atomizing gas in wire arc spray is improved by using super sonic cold gas (non combustion gas) jet for better coating characteristics. To generate the super sonic cold gas jet, one is an optimization of nozzle shape with conventional compressed gas and another is that the pressed gas heated at 500-800K is supply to converging-diverging nozzle. Namely, coating deposition mechanism of cold spray, which is high particle impact velocity to substrate, is applied to wire arc spray. In this study, gas dynamics investigated the effect of pressure and temperature of supplied nitrogen gas, nozzle geometry on wire arc spray process (thermodynamical behavior of atomizing gas and coating properties).

High Velocity Oxy-Fuel (HVOF) method using propylene as a fuel gas was employed to spray alumina particles. In order to improve the coating characteristics such as the deposition efficiency and the hardness, three HVOF gun nozzles of varying geometry were designed and tested experimentally. The spraying process was also simulated numerically for each of the nozzle geometries to understand their effectiveness in influencing the velocity and temperature of the sprayed particles. The coating was characterized using optical and scanning electron microscopy (SEM), micro-vickers hardness test and X-ray diffractometry (XRD). Results showed that with the use of a convergent and divergent type gun nozzle, similar to that of a Laval nozzle, the extent of melting of the alumina particles could be increased. This was exhibited by an increase in the deposition efficiency to the extent of 45%. However, the sharp changes in the convergent and divergent nozzle geometry, resulted in fusion and agglomeration of alumina particles leading to spitting during the spraying process. The results clearly showed that alumina coatings of excellent hardness in the range of 920-1290 HV, with a relatively dense microstructure could be obtained in HVOF method irrespective of the gun nozzle geometry, provided the spraying parameters are properly controlled.

Nozzle geometry has a profound effect on HVOF spraying, influencing combustion gas dynamics as well as particle behavior. Nozzle dimensions are also important in cold gas-dynamic spraying (CGDS), particularly the length of the nozzle which affects gas flow temperature and speed. In this study, numerical simulations and experiments were conducted to determine how the length of the entrance convergent section of gun nozzles affects HVOF spraying. Process changes that occur inside the nozzle (as predicted by simulation) were correlated with coating properties. An Al2O3-TiO2 powder was used for the experimental studies. Changes in nozzle length had a significant impact on deposition efficiency, microstructure, hardness, and particle velocity. These relationships (as measured and calculated) were then applied to the nozzle design for the CGDS method.

Effect of nozzle geometry (such as throat diameter of a barrel nozzle, exit diameter and exit divergence angle of a divergent nozzle) on HVOF thermal spraying process (thermodynamical behavior of combustion gas and spray particles) was investigated by numerical simulation and experiments with Jet Kote II system. The process changes inside the nozzle as obtained by numerical simulation studies were related to the coating properties. A NiCrAlY alloy powder was used for the experimental studies. While the throat diameter of the barrel nozzle was found to have only a slight effect on the microstructure, hardness, oxygen content and deposition efficiency of the coatings, the change in divergent section length (rather than exit diameter and exit divergence angle) had a significant effect. With increase in divergent section length of the nozzle, the amount of oxide content of the NiCrAlY coatings decreased and the deposition efficiency increased significantly. Also, with increase in the exit diameter of the divergent nozzle, the gas temperature and the degree of melting of the particle decreased. On the other hand the calculated particle velocity showed a slight increase while the gas velocity increased significantly.