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.

Cold spray is continuously expanding for the repair of parts made of aluminum-based alloys. Beyond repair applications, the process is now expected to be exploited efficiently for the additive manufacturing of shaped parts. However, up to now, cold spray is limited to the achievement of rather simple shapes due to a lack of basic knowledge on coating build-up mechanisms to result in dimension-controlled deposition. The objective of this work is to fill that gap through an experimental and modeling study of the coating build-up in cold spray for this specific application. Experimentally, Al-based coatings were deposited for a large range of particle velocity due to the use of low-pressure, medium-pressure and high-pressure cold spray facilities. Particle velocity was monitored as a function of cold spray conditions. Two different types of Al 2024 (Aluminium 2024 Alloy) powders were tested. Coating porosity and microhardness were studied as a function of (both morphological and metallurgical) powder characteristics and spray conditions, primarily in the light of particle velocity. Various correlations could be exhibited. Finite element (FE) simulations of particle impacts were developed, including particle velocity from experimental measurements. These will be used as inputs in an in-house morphological model, the first stages of which could be established successfully.

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. 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 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 behaviors of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. We have studied copper particles so far. In this study, we will examine aluminum particles. First, we investigate the influence of the size and shape of the rectangular section nozzle on the velocity, temperature, and particle distribution of aluminum particles by CFD. After that, the rectangular section nozzles were fabricated and coating formation experiments were conducted, spray patterns and coating cross-sectional structures were observed, and coating adhesion was also evaluated. The nozzle material was polybenzimidazole resin, which is difficult for aluminum particles to attach to nozzle walls.

This study examines the structural and corrosion properties of Ni and NiCu coatings produced by high-pressure cold spraying. It also assesses the effect of heat treatment. FE-SEM images of coating cross-sections show tightly bonded particles with only a minor presence of open or oxidized boundaries. Polarization measurements in alkaline salt and acid solutions show that the Ni and NiCu coatings have good potential for corrosion protection applications. Corrosion behaviors of as-sprayed and heat treated coatings are compared with corresponding properties of bulk and substrate materials.

High-pressure cold spraying has shown significant potential in manufacturing metallic composite coatings for a wide range of industrial applications, including wear and corrosion protection. Quasi-crystalline materials, in turn, are promising candidates due to their unique microstructural features. Combining these concepts, metallic composite coatings were generated using high-pressure cold spraying to produce functional and protective coatings. Several spray trials were done to detect the effect of compositions and size of quasi-crystalline feedstock materials mixed with metal powders, Al6061, and stainless steel 316L, on coating microstructure, integrity, and surface properties. A scanning electron microscope was used to examine the microstructure of the feedstock materials and composite coatings. A 3D surface optical profilometer was also used to investigate surface texture. The wettability of the coating surfaces was measured by static water contact angles using a droplet shape analyzer. Cold-sprayed quasi-crystalline composite coatings showed denser and well-integrated deposits with a random distribution of phases across the composite surface, indicating promising structural reliability and hydrophobic behavior.

The footprint of a cold spray beam has narrow dimensions and a large particle density, which lead to fast growth of deposit on precise locations. Cold spray produces compressively stressed coatings which lead to well bonded ultrathick coatings over many substrates. Since cold spray produces dense coatings with wrought-like microstructure, it can be used to produce large bulk forms. Two different bulk forms were produced: (i) ultrathick coatings strongly bonded to substrates and (ii) free standing structures (FSS). Both forms were post machined to obtain net-shape or near-net-shape articles. Bulk forms up to 60 mm were produced with many powders including metals, alloys and composites. Well bonded ultrathick coatings were produced over many substrates including aluminum, copper, SS, etc. FSS, including pipes, plates, etc, were produced by fabrication of a mandrel, spray coating bulk forms and removal of the mandrel. Coatings in the as-sprayed condition were machined and fine features such as grooves incorporated to obtain net-shape articles.

Cold spraying is a semi-empirical method in that spray parameters must be optimized experimentally in regard to coating quality and deposition efficiency. In this work, porosity and deposition efficiency are the key parameters in the optimization of corrosion-resistant zinc coatings produced by high-pressure cold spraying. The deposition process is described along with the tests used to assess the morphology, adhesion, and anticorrosion properties of the coatings obtained.

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.

Cold spray produces superior coatings with many unique properties, which have led to many new applications of sprayed coatings. In a few applications, such as in-situ repair of aircraft body/engine parts, etc., a portable system is required. Though some portable low pressure (5 – 10 bars) systems are available, these systems have many limitations on coating materials and coating qualities. Recently a ‘Portable high pressure cold spray system’, called Kinetiks 2000, has been developed. Kinetiks 2000 system can operate at 400 °C max nitrogen temperature and 20 bars max gas pressure. A touch panel on the console is used to input and control the process parameters. A hand held gun with a filament heater and a gun body, mounted directly onto the heater, is used for manual spray. This system operates with two different powder hoppers. Coatings of many materials, including aluminum, copper, titanium, zinc, etc have been produced. Microstructural investigations of sprayed coatings have shown that good, strong, dense coatings with clean interfaces and strong bonding to various substrates can be produced. Experiments are continuing to quantify the process characteristics and record the properties of sprayed coatings.

This study investigates the effect of water injection in the high pressure chamber of a cold spray nozzle. A de Laval nozzle geometry with constant back pressure and temperature is modeled numerically using Reynolds Stress Model coupled equations. Water spray with a droplet size of 10 – 100 μm is modeled using both uniform and Rosin-Rammler size distributions. The two-phase flow of gas-liquid is modeled using an unsteady discrete phase mass source with two-way coupling with the main gas flow. Upon injection, the droplets in the water spray evaporate while travelling through the nozzle due to momentum and energy exchange with the gas flow. The evaporation behavior in presence of water content is modeled and a correlation between the initial diameter and the diameter just before the throat is obtained. As a result, the proper droplet size distribution with a fully evaporative spray can be used as a carrier of nano-particles in cold spray nozzles. Having the results, guide us to substitute the un-evaporated part of the droplet with an equal diameter agglomerate of nano particles and find a minimum fraction of nano particles suspended in the liquid which guarantees fully evaporative liquid spray injection.

Superior characteristics of the cold sprayed coating have led to many high-tech applications. Until recently, all these applications were carried out using ‘stationary’ systems only, while some applications such as in-situ repair of aircraft body/engine parts require a portable system. Recently a ‘Portable High Pressure Cold Spray System’ called KINETIKS 2000-2 has been developed. This system is capable of 400 C/20 bars nitrogen/helium jet, and produces dense coatings with clean interfaces of many materials. In order to establish the suitability of this process for producing aluminum alloy coatings for aerospace and other high tech industries, various aluminum alloys (CP-Al, HP-Al, 6061 Al, 7005 Al) coatings were produced over many substrate materials (2024 Al, 7005 Al, 4041 Steel, ZE41A Mg). Coatings were characterized using microstructure, bond strength, bend test, corrosion studies, etc. Microstructural study showed that dense coatings with about 2-4% porosity values were produced with clean and well bonded interfaces. Bond strength of these coatings varied between 20 to 35 MPa, Bend test results showed that the coatings have adequate strengths and could withstand severe strain conditions. Salt fog corrosion studies (ASTM B 117) showed that the coatings impart corrosion resistance to the substrates.

The US Navy has adopted High-Pressure Cold Spray (HPCS) as a repair technique for corroded and worn components in their fleet of aircrafts, ships, and submarines. HPCS repairs are not only used for depositing corrosion and wear resistant coatings but is being successfully used for dimensional restoration in metal parts and components. By utilizing HPCS, the Navy ensures the longevity and reliability of critical components, even in harsh environments. Whether safeguarding against corrosion or restoring worn parts, HPCS is playing an increasingly critical role in maintaining operational readiness for the US Navy and other DOD agencies, as well as the commercial industry.

The rapid emergence of cold spray technology provides numerous applications that require spraying fine (<10 microns) powders, providing more uniform deposition, improved measurement of deposition efficiency and quick turn around time. The performance of high-pressure commercial powder feeders, currently available, lacks one or more of these desired performance characteristics. Further, researchers are interested in spraying many powders of different materials or particle size distributions where the powder feeder can be quickly and easily cleaned without replacing expensive consumables. The Ktech laboratory powder feeder has been designed to operate under a wide variety of carrier gas pressures (0 – 500 psig). This laboratory feeder delivers a continuous flow of powder, has a variable canister volume and is quick and easy to clean. This unique design facilitates short run research applications or higher volume extended run time dispensing. The feeder is designed to operate in either a locally or remotely through a PC based Ethernet connection. The laboratory powder feeder represents an excellent tool for high-pressure cold spray or low-pressure thermal spray processes requiring the delivery of fine powders.

In this work, fully dense titanium parts are fabricated by cold gas dynamic spraying (CGDS). Titanium powder is deposited using a low-pressure CGDS process with nitrogen as the carrier gas. The density, porosity, hardness, and tensile properties of the parts produced are determined and discussed.

Cold spray (CS) is a progressive method for the deposition of metals and alloys whose principles involve considerable plastic deformation of the produced material at extreme strain rates. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the PAS method was used to characterize the deformation character at the lattice level and quantify the open-volume defects in four cold sprayed metals: Al, Cu, Ni, and Ti. As counterparts, bulk samples of these materials with ultrafine-grained structures were also produced by high-pressure torsion (HPT), a process exceeding cold spray in the total deformation, but having several orders of magnitude smaller strain rates, and by a traditional cold rolling process. The results show that the CS and HPT processes lead to the formation of similar lattice defects (dislocations and vacancy clusters), and both exhibit significantly higher dislocation densities than conventionally cold-rolled materials. Further, the vacancy clusters present in CS and HPT materials were not present in the rolled counterparts due to the lower vacancy production rate.

Cold spray is a reduced temperature, supersonic thermal spray process that is increasingly being used to perform repairs on high value components. In this case, a valve actuator internal bore sealing surface was repaired on an aluminum 6061 hydraulic valve body using high pressure cold spray. Corrosion damage to non-critical surfaces was also repaired, allowing the part to be returned to service. The VRC Gen III high-pressure cold spray system was used to deposit gas atomized 6061 aluminum powder. The internal bore surfaces were approximately 100 mm in diameter with a depth of nearly 200 mm, and were sprayed using a 45-degree nozzle 65 mm in length. The minimum required adhesion strength on critical surfaces was 69 MPa. The average adhesion strength was 71.4 MPa, with glue failures on ASTM C633 bond test specimens.

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.

Iron based coatings have recently gained much attention as they have favorable mechanical, frictional, and corrosion properties. The coatings possessed a high content of iron borides are particularly valuable for satisfying engineering needs. Boron and iron form two major boride phases, FeB and Fe2B, with different mechanical and thermal properties. Orthorhombic boride FeB is considered to be viable candidate to enhance the surface hardness and wear resistance of components, since it has high hardness. Producing of such coating by cold spray method is considered to be an alternative for boronizing method which is a conventional thermochemical surface hardening process. In this work, the crushed ferroboron (FeB) powders of Fe-17.9B-0.4C-1.6Si-0.3Al (wt. %) were deposited onto low carbon steel substrate by cold spraying. However, low and high pressure cold spraying allowed depositing very thin and single layer on the substrate, due to the intrinsic brittleness of the powder. Therefore, several contents of Al, Ni and Fe metallic powder and their combinations were added to FeB powder to obtain thick coating via cold spray processes. Post heat treated coatings at a temperature of 700 °C resulted in increase of the hardness, possibly the formation of hard phases such as intermetallic compound.

Cold spray has been successfully used to produce WC-Co coatings in recent years, showing great potential. However, due to the lack of sufficient Co matrix phase for plastic deformation, the fabrication of cold sprayed WC-Co coating naturally requires expensive propulsive gas or very high working parameters, significantly increasing the manufacturing difficulty and cost. This paper aims to use conventional high pressure cold spray to fabricate high-performance and cost-effective WC-Co-Ni coatings, and to clarify its formation mechanism. To achieve this objective, mechanically mixed porous WC-17Co and dense Ni powders were selected as the feedstock with different WC mass fraction, F1 (41.5 wt.%), F2 (64.5 wt.%) and F3 (74.7 wt.%). Working parameters were set at a moderate level (nitrogen, 3.0MPa and 350°C) to control the experimental cost. Experimental results showed that WC reinforcements had no phase transformation and were completely retained in the WC-Co-Ni coatings. The highest WC mass fraction was present in the F3 coating, reaching approximately 75% (equivalent to the feedstock), quite close to the cold sprayed WC-25Co coating. Fracture of WC-Co particles during the deposition process was found to be the reason for such high WC retainability, dominating the coating formation mechanism.

Cold spraying enables the production of pure and dense metallic coatings with very little porosity and oxygen content, all of which play an important role in corrosion resistance. This study investigates the microstructure, denseness (impermeability), and corrosion properties of tantalum coatings produced by high-pressure cold spraying. Various tests were conducted to assess corrosion behaviors in different aqueous solutions. Microstructural studies showed that interfaces in the coatings were practically free of voids and confirmed that high levels of localized plastic deformation occurred as expected during spraying. The study also confirmed that the polarization behavior of the cold-sprayed tantalum is similar to that of the corresponding tantalum bulk in saline as well as sulfuric and hydrochloric acid solutions.