This study compares the deposition behavior of kinetic sprayed bronze-diamond composite coatings produced using different mixtures of helium and nitrogen gas. To determine impact properties of the diamond particles, bare and nickel-coated diamonds are deposited on bronze layers and the effects of plastic deformation are examined using SEM and finite-element analysis. The results indicate that the deposition efficiency of diamond is determined by several factors and depends more on the angle and shape of the diamond particles than on the deformation properties of the bronze matrix.

This study assesses the effectiveness of nickel-coated diamond powder for producing metal-diamond composite coatings by cold spraying. The results of the investigation show that diamond fracturing was mitigated by the protective nickel coating. In general, the softer the metal matrix and the finer the diamond, the less fracturing that occurs and the greater the diamond fraction in the composite layer. It is also shown, however, that deposition efficiency and diamond fraction must be improved especially for diamond sizes of 50 μm and above.

In the present investigation, thermally enhanced kinetic spraying of titanium onto mild steel substrates is carried out in conjunction with powder preheating to obtain a dense coating using low-cost nitrogen as the process gas. Prior to this, a prototype model was developed for process optimization based on numerically approximated adhesion factors. The simulation results show that adiabatic shear instability accelerated by thermal energy and subsequent particle impact leads to the formation of an enhanced thermal boost-up zone that closely correlates with deposition behavior and coating properties. It is thus shown that the deposition efficiency of titanium can be more than 90% and porosity less than 1% when nitrogen gas is used for cold spraying.

Manufacturing of diamond abrasive wheel has been achieved through kinetic spraying in order to simplify the manufacturing process and improve the mechanical properties. However, size of the initial feedstock diamond particles is reduced by fracturing during the process. Uniform distribution of diamond particles in the coating layer is significantly important for obtaining grinding properties of diamond abrasive wheel. In this study, optimized nickel thin film which is coated around the surface of diamond particle was used to prevent the fracture of diamond particles during spraying and improve the properties. Thickness of the nickel thin film was optimized by ABAQUS 6.7-2 finite element analysis software as 3 µm for 20 µm diamond and bronze particles. Fraction and size distribution of the diamond particles present in the coating were analyzed through Scanning Electron Microscope (SEM) and Image analyzer methods.

In this study, Al-Sn binary alloy coatings were prepared with Al-5wt.%Sn (Al-5Sn) and Al-10wt.%Sn (Al-10Sn) gas atomized powders by low pressure and high pressure cold spray process. The microstructure and microhardness of the coatings were characterized. The as-sprayed coating were heat treated at 150, 200, 250 and 300 °C for 1 hour, respectively. The effect of heat treatment on microstructure, microhardness and content of Sn phase of the coatings were investigated. The bonding strength of as-sprayed and heat treated Al-Sn coatings were also studied. The results show that the dense and well-bonded Al-10Sn coating can be deposited by low pressure with helium gas while Al-5Sn coating by high pressure cold spray with nitrogen gas. The content of Sn for both Al-5Sn and Al- 10Sn in as-sprayed coatings are consistent with that in feed stock powders. The coarsening and/or migration of Sn phase in both coatings were observed when the annealing temperature exceeds 200 °C. Furthermore, the microhardness of the coatings decreased significantly under the annealing temperature of 250 °C. EDAX analysis shows that the heat treatment has no significant effect on content of Sn phase in Al-5Sn coatings. Bonding strength of as-sprayed Al-10Sn coating is slightly higher than that of Al-5Sn coating. Annealing under 200 °C can increase the bonding strength of Al-5Sn coatings.

The conventional manufacturing process of the automotive brazed heat exchanger includes complex preparation processes before brazing: aluminum brazing filler alloy is pre-claded on both sides of a fin by an extrusion method, and holed aluminum tubes are coated on both sides with Zn for corrosion protection by a wire arc spraying process. The intent of this study is to simplify the preparation process by kinetic spraying using all of the components, including Al-12%Si (for the brazing filler metal), Zn (for corrosion protection), and KAlF4 (flux powder). Four kinds of blended powder, with and without flux, were evaluated. The bond properties and composition distribution at the braze joint area were evaluated by SEM and an electron probe micro analyzer (EPMA). It was necessary to control the Zn content so that the corrosion resistance and brazeability of the aluminum heat exchanger would not be affected. An optimal kinetic spray condition was obtained, in order to fabricate the heat exchanger in this study. It was observed that the joints of the brazed specimens on each side of the brazing part were sounder than those achieved brazed by the conventional methods. Further, the kinetic sprayed heat exchanger showed acceptable corrosion protection.

The deformation behavior and mechanical properties of a Cu 54 Zr 22 Ti 18 Ni 6 bulk metallic glass during and after deposition by kinetic spraying were investigated. The bulk metallic glass feedstock particles were manufactured by inert gas atomization and were subsequently deposited onto mild steel substrates by means of kinetic spraying at different powder carrier gas temperatures [room temperature, 450°C (within the supercooled liquid region), and 550°C (above crystallization temperature)]. In addition, the phase compositions of the feedstock and as-sprayed BMG coatings were investigated using X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), and Transmitted Electron Microscopy (TEM). With an increase of the powder feed temperature, it was deduced that more intimate contact of the particles with the substrate was achieved which decreased the porosity of the resulting coating. However, crystallizations, which seemed to be induced by severe deformation and accumulated heat, were observed at localized regions in the coating. In addition, micro-hardness and bond strength were affected by the crystallization degree of the as-sprayed coatings

The aim of this study was to ascertain the optimal process parameters that minimized compositional variation between the original powder mixture and composite coating. A bronze- 20 vol.% diamond composite powder was deposited by a kinetic spraying process with various feed rates, spraying distances and particle velocities. Experimental results showed that the diamond fraction, deposition efficiency and bond strength were dependent on process parameters, in particular, the particle velocity.

Thick metal/diamond composite coatings on Al substrate were deposited by cold spray process with in-situ powder preheating. Microstructural characterization of the as-sprayed coatings with different diamond size, strength and with/without Ti clad coating was carried out by OM and SEM. Assessment of basic properties such as tensile bond strength, porosity, and hardness of the coatings and the deposition efficiency was also carried out. Particular attention on the coatings was on the diamond fracture phenomenon during the cold spray deposition and the interface bonding between diamond and metal matrix. The potentials and the problems of metal/diamond composite coatings by cold spray are discussed.

This study evaluated the effects of particle temperature on deposition efficiency and critical velocity in kinetic spraying. A wide range of pressures and preheat temperatures of the process gas were used in these experiments to vary both particle velocity and temperature, and a bronze (Cu-Sn alloy) powder was deposited onto aluminum and bronze substrates. The deposition efficiency of the coatings was measured, and the critical velocity was estimated. The experimental results showed that the critical velocities of the bronze feedstock deposited onto either an aluminum or bronze substrate were different and that the critical velocity was strongly dependent on the particle temperature, which when increased, caused the critical velocity to decrease. Increasing the gas pressure caused an increase in particle velocity, while increases in the gas temperature not only affected the particle velocity but also the particle temperature. In our experiments, the critical velocity decreased by 50 m/s when the process gas temperature increased by 100 °C.

Critical velocity has been accepted as a characteristic property of kinetic spraying (or cold gas dynamic spraying), which works by accelerating small solid particles to supersonic velocities and then impacting them onto a substrate. However, there is a lack of information about the impact of individual particles and their deposition behavior over a large range of impact velocities. To probe into the impact behavior of the particles and to elucidate the deposition mechanism, individual particle impaction tests have been carried out. A rebound phenomenon was found to occur at a high impact velocities, in which a large fraction of the particles rebounded. Based on experimental results, a model of a plastic particle impacting onto an un-deformed substrate was developed. The adhesion and rebound energies were calculated to estimate the particle/substrate interactions. A maximum impact velocity was found for particle deposition onto the substrate. The particle deposition behavior was controlled by the adhesion and rebound energies.

Kinetic spraying process that is basically a solid-state deposition process was used for the formation of a fully amorphous coating. As the application of pre-heating system for the powder carrier gas and using Helium for the process gas, it was possible to form of amorphous coating. Main process parameters evaluated in this study were gas species[N 2 and He]and pre-heating temperature[RT(below Tg) and 550 (liquid metallic region)] for carrier gas. Aside from empirical approach, in-flight particle velocity within kinetic spraying process was measured with spray-watch- 2i. The deposition behaviors of a NiTiZrSiSn bulk amorphous powder were observed when it was sprayed using kinetic spraying process. When the bulk amorphous feedstock material was coated, both kinetic energy and thermal energy of the in-flight particle are important. The former did affect on the deposition of the bulk amorphous coating, while the later did more affect on mechanical properties of coating. Particle deposition behaviors were considered from the viewpoint of the environmental effect such as particle energy combination on the deposition behaviors. The bonding of the impacting NiTiZrSiSn bulk amorphous particle was primarily dependent on the temperature dependent deformation and fracture(local liquid drop formation) behavior.

The cold spray process is a relatively new process using high velocity metallic particles for surface modifications. Metallic powder particles which are injected into a converging-diverging nozzle are accelerated to supersonic velocities. In this study two-dimensional temperature and velocity distributions of gas along the nozzle axis are calculated and the effects of gas pressure and temperatures on particle velocities and temperatures inside and outside of the nozzle are also investigated. It is found that the acceleration of the gas velocity takes place in the area of the nozzle throat and it increases and reaches maximum value at the nozzle exit. Due to compression shocks in the area after the nozzle, the gas jet properties show irregular shape and these result in the existence of the maximum particle velocity by the change of particle size at a given gas pressure and temperature.

WC-Co powders with nano-sized WC were deposited by dynamic powder deposition process. Microstructural characterization and phase analysis of feedstock powders with different compositions and as-deposited coatings with various substrates were carried out by SEM and XRD. The results show that there is no detrimental phase transformation and/or decarburization of WC by dynamic powder deposition. It is also observed that nano-sized WC in the feedstock powder is maintained in the deposited coatings. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coatings with low porosity and very high hardness by dynamic powder deposition.

Characterization of flame sprayed and furnace fused NiCrBSiC alloy coatings with two different carbon contents and 15~45 wt.% WC-Co addition is described in terms of microstructure, microhardness, and differential thermal analysis. Microstructural development of these coatings before and after fusing treatment is discussed to identify the precipitates in the coatings. Optimum fusing conditions (time and temperature) for wear testing sample are investigated in terms of microhardness and porosity of the coatings. Wear performance of these coatings is also investigated by two-body and three-body abrasive and dry sliding wear experiments. Optimum tungsten carbide content of the coatings is also selected to improve wear performance and thus enhance the service life of the process roll for cold rolling steel plant. Finally, microstructure and microhardness of the furnace and induction fused coatings are compared with emphasis on the interface between the coating and the steel substrate.

This investigation was conducted to clarify the effects of process parameters on the formation of the new amorphous coating using Zr-based alloy, which is known as bulk metallic glass forming alloy, by a HVOF (High Velocity Oxygen Fuel) spraying process. Powders used for spraying was prepared by vacuum gas atomization and then crushed by a centrifugal mill. HVOF spraying experiments were carried out using a Tafa JP-5000 spraying gun. DTA (Differential Thermal Analysis) measurements have shown that the amorphous content of the coatings was measured up to about 65% depending on the spraying parameters. The amorphous fraction of the coatings is decreased with increasing the spray distance and the fuel flow rate. Microstructural observations and X-ray diffraction analysis of the spray coated layers reveal that the amorphization behavior during the spraying is attributed to the degree of the solidification of droplets and the oxide (ZrO2) formation in spray coated layers. Therefore, flame temperature and spray distance that can control the carrier gas temperature and undercooling effects of the droplets are the most crucial factors for the evolution of the amorphous phase using this bulk metallic glass forming alloy.