Cold spray is a solid-state metal powder deposition technique that has proven to be highly effective in depositing a wide range of metals, including aluminum and its alloys. However, higher strength, heat treatable Al alloys appear to exhibit variable deposition efficiencies and responses to heat treatments designed to increase ductility. This work is aimed at understanding the sources of these variabilities. In this study, 6061 (0.9% Mg, 0.6% Si, 0.3% Cu, 0.1% Cr, 0.1% Fe) alloy is compared to 7075 (6% Zn, 1.6% Cu, 2.4% Mg, 0.2% Cr, 0.3% Fe) alloy. These are common heat treatable alloys, but they exhibit quite different cold spray characteristics. Generally, 7075 is more problematic in terms of deposition efficiency and the mechanical properties after heat treatment. The alloys were processed under various cold spray conditions, including laser assisted cold spray designed to soften the 7075, and subjected to heat treatments intended to increase ductility. The microstructure and mechanical properties of the as sprayed and heat-treated coatings were characterized and compared. The results of this investigation will reveal possible mechanisms explaining the different cold spray behaviors and some suggestions will be proposed to overcome the problems associated with 7075.

Tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs) in previous studies at McGill University and a “crack-filling” mechanism was described as the mechanism that allowed deposition of the metal onto the composite counterpart. By adding other metal powders (aluminum, copper, zinc), it was possible to improve the deposition efficiency (DE) of the tin on the CFRP, as well as improve the electrical conductivity of the coating (notably with copper). While the effect of mixing powders with tin, and more notably the effect of the secondary component (SC) properties on the deposition improvement, were more thoroughly addressed in following studies, the question of the properties of these coatings remained. With the perspective of providing a metallic coating to a relatively poorly conductive composite substrate, this study aims to explore the electrical conductivity and the coating strength of cold sprayed tin with other SCs onto CFRPs. An extensive study on fractured surfaces highlighted the importance of the CFRP surface finish, and it was observed that the coating strengths improved with decreasing DE of pure tin.

Previous results at McGill University have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fibre reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a bench mark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK, and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI.

In this work, single component 316L and Fe coatings, as well as mixed 316L/Fe coatings with a dual powder feeder to obtain various feedstock compositions, were deposited to measure the deposition efficiency (DE). Individual particle impact tests were performed on single component and composite coatings to understand the particle impact behaviors during deposition. Bond ratio (BR) were determined for the impact tests to correlate with the DE. Results show that the 316L powder has a better DE than Fe, whereas the DE of the mixed 316L/Fe powders increases with increasing feedstock Fe content. The BR results correspond well with the DE of single component powders and mixed powders. The BR of 316L impacts onto composite coatings decreases with increasing Fe content, while the BR of Fe impacts plateaus at a high value regardless of composite coating composition, which leads to the increase of overall mixture DE.

In this study, stainless steel powder is mixed with commercially pure iron and cold sprayed on steel in order to produce a metal composite with controlled properties. For these composites, porosity is very low, and annealing at 600-1100°C for an hour reduces it further. Annealing also sinters interparticle interfaces, leading to vastly improved fracture properties. Fully annealed single-component stainless steel exhibits a much higher strength than annealed CP iron, but adding just 20% stainless steel to iron produces a composite with the same fully annealed strength as that of stainless steel.

In this work, metallic powders are applied to carbon fiber reinforced polymer (CFRP) substrates by low-pressure cold spraying. The coatings as well as the coating-substrate interfaces are characterized and the deposition mechanism is determined. It is shown that gas temperatures above 300°C are required for the continuous deposition of tin. These temperatures bring about partially melting, which facilitates adhesion. Accordingly, a “crack filling” mechanism is proposed to explain the deposition.

The aim of this work is to cold spray a metal coating with sound mechanical properties and good electrical and thermal conductivity on carbon fiber reinforced polymer (CFRP) substrates. Copper, aluminum, and tin were used as the coating materials and different gas pressure and preheating temperature combinations were employed during spraying. Erosion was found to be the key obstacle to develop continuous coatings, although embedded particles were observed in the residual epoxy.

In this investigation, Inconel 718, a material known to cause nozzle clogging upon cold spraying, was cold spray formed to 6 mm-thick using the Plasma Giken cold spray system PCS- 1000. This was made possible due to the novel non-clogging nozzle material combined with a nozzle water cooling system. Coatings were as-spray formed using both nitrogen and helium as the propelling gasses. The resulting microstructures as well as the corresponding mechanical properties were studied. In addition, the effect of post-heat treatments was also investigated. It was found that for a given propelling gas used, the coating porosity level remained relatively similar (about 2.4% for nitrogen and 3.6% for helium) regardless of the coating treatment (as-sprayed or heat treated). Visual inspection from SEM micrographs showed a higher fraction of inter-particle metallurgical bonds for nitrogen gas sprayed coatings heat treated at 1250°C for 1 hour due to some sintering effect. This significantly affected its tensile properties with an average resulting ductility of 24.7%.

This research systematically examines the effect of heat treatment on the microstructural properties of cold sprayed titanium coatings. Heat treatments were performed on as-sprayed coatings at 200, 400, 600, and 800°C for four hours under argon atmosphere. Vickers microhardness, microstructural investigation using FEG-SEM, structural characterization using XRD, and porosity evaluation using SEM image analysis were performed on as-sprayed and heat treated coatings. Results demonstrated that static recovery and static recrystallization may have occurred for heat treated coatings at 600 and 800°C. In addition, for the heat treated coating at 800°C, significant oxidation occurred and a slight decrease in porosity took place. Furthermore, a thin metallic layer characteristic of a solid solution or an intermetallic compound, was found at the coating/substrate interface.

This study reports on the effect of combined pulsed laser ablation and laser pre-heating surface pre-treatments to cold spraying Ti and Ti-6Al-4V on coatings’ microstructure, bond strength and cohesive strength. The Ti and Ti-6Al- 4V coatings were sprayed on pure titanium and Ti-6Al-4V substrates, respectively. Coatings were characterized by SEM and porosity level was evaluated through image analysis. Bond strength was evaluated by standard ASTM C633 pull tests and by the laser shock (LASAT) technique. Cohesive strength was evaluated by the cross-section scratch test method. Results show that among the spray conditions used in this study, laser pre-treatment yielded high bond strength (such that all cases had higher cohesive strength than the epoxy glue). The LASAT technique provided a means to evaluate the influence of the laser ablation energy density and the laser pre-heating temperature. For both Ti and Ti-6Al-4V coatings, surface pre-heating increased the coating bond strength to the substrate. The laser ablation process would either increase or decrease the bond strength of the coating to the substrate depending on the laser energy density. The laser energy density needs to be adjusted as a function of the surface pre-heating temperature in order to optimize bond strength improvement. Coating cohesion did not improve with continuous laser pre-treatment in-between passes. However, the laser pre-heating helped reduce the coating porosity.

This paper reports on the influence of the He to N 2 ratio on the properties of low pressure cold sprayed titanium coatings and on the characteristics of the generated supersonic two-phase flow. Experiments were carried out varying the He to N 2 concentration ranging from pure He to pure N 2 . Samples were characterized by their microstructural properties (i.e. microhardness and porosity). Deposition rate was evaluated and particle velocities were measured for all conditions. Deposition efficiency, coating density, and microhardness were found to be a function of particle impact velocity. Velocity data were used to validate a computational fluid dynamic model. The numerical solution of the flow inside the nozzle was obtained from the Euler equations for the various He to N 2 concentrations. Particle tracking was carried out by using the computed distribution of density, Mach number, temperature, viscosity, and a second order Runge-Kutta scheme. In addition, mean particle velocities at the exit of the nozzle were determined. Computed velocities were found to be in good agreement with measured ones. The model was then used to calculate nozzle dimensions that would maximize particle velocity. Optimized dimensions are proposed.

This study investigated the effect of the type of gas used, nitrogen and helium, during cold spraying of titanium coatings. In all conditions, the propelling gases’ temperature and pressure were attuned to attain three similar particle velocities for each gas. Coatings were characterized by SEM and XPS. Deposition efficiency, coating microhardness, and porosity were evaluated for all conditions. Results show that for the same particle impact velocity, the deposition efficiency and coating density were mostly the function of the surface temperature, which in turn was influenced by spray parameters. It is shown that loosely-bonded particles at the surface can be detached by the passage of high pressure supersonic gas stream. In addition, a thick and fully dense cold sprayed titanium coating was achieved with optimized spray parameters with He and the corresponding average particle velocity was measured at 1173 m/s.

This paper describes and evaluates the performance of a Helium Recovery System (HRS) designed for cold spraying. A flexible, automated, full scale HRS system has been designed and installed in the McGill Aerospace Materials & Alloy Development Center Cold Spray Facility, located at and in collaboration with the National Research Council of Canada. The fully automated HRS has been designed to recover helium from the cold spray chamber with sufficient purity (>99%) and flow capacity (5 to 220 Nm 3 /h), allowing for a cost-effective operation by insuring a recovery rate of above 85%. In addition, a comparison of titanium coating properties obtained by using both He and N 2 as propellant gas is presented.

Cold spraying is particularly suitable for elaborating heat and oxidation sensitive coatings. Due to the fact that the particles are not melted during the spraying process, it is thus possible to elaborate coatings without chemical modifications. Nevertheless, according to the materials considered, some interface defects can be detected inducing an inadequate adhesion between the substrate and the coating. Bonding mechanisms are not only strongly dependent on the particle velocity but also on the state of the surfaces. By this way, surface pre-treatments can be necessary to improve adhesion. From all the surface modification technologies, laser ablation process is very interesting due to its flexibility by using optical fibers and due to the perfect control over the treated area. It is then possible to interact with the material during all the spraying process on the substrate surface as well as on the interface layers. This is particularly the aim of this study which consists in exploring the laser influence, implementing the PROTAL process, on the different interfaces quality for coatings elaborated by cold spray on metallic substrates. By controlling the chemical composition of the materials, the coating cohesion as well as the adhesion level, coatings were sprayed on pure titanium and titanium and nickel based alloy substrates.

This work investigates the influence of nitrogen gas pressure and temperature on the structure and properties of cold sprayed titanium coatings. Two guns were used to assess the effect of impinging particle temperature. Particle speed was measured and used to calculate critical velocity for selected experimental conditions. The results show that increasing the temperature and pressure of the gas propellant reduces coating porosity and increases hardness, flattening ratio, and deposition efficiency. At the maximum pressure and temperature (40 bar and 800 °C) for nitrogen gas, coating density was close to the value reported for cold sprayed titanium produced using helium as the propellant.

The properties of pure Cu, Ni and Ti cold spray coatings on mild steel substrates were examined. Samples were prepared using CGTTM Kinetics 3000 system varying gun temperatures from 200 to 600 °C and gun pressures from 10 to 30 bars with N 2 as propelling gas. For these conditions, deposition efficiencies and critical velocities were characterized. In addition, the microstructural and mechanical properties of coatings were examined.