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 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 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 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.