Thermal spray (TS) technology has attracted the attention of numerous industrial sectors due to its apparent simplicity and versatility. It has been used across the world for over 80 years in the conservation and creation of art. Despite the creativity involved in the creation of an art piece, the TS artistic endeavors are limited and insufficiently explored. Unique material combinations, usually not observed in conventional engineering applications, can be achieved with TS technology. Although the material amalgamation possibilities are infinite, their combined deposited characteristics, interfacial compatibility and color palette require further study. In this work, the fields of photography, image processing and TS are combined to produce a large art-piece using the cold gas dynamic spray (CGDS) process. Aluminum, zinc, nickel, alumina, steel and titanium alloy powders are sprayed to replicate in three-dimensions a photograph of a crinoid from the Silurian period found on the Anticosti Island, located in the Gulf of St. Lawrence in Canada. The numerous steps required to produce the artistic 3D piece, namely numerical segmentation of the photograph, conversion to a computer-assisted design (CAD), manufacturing of steel masks and CGDS deposition of the selected powders to reach the sought color palette are described. Powder deposition efficiency, material compatibility and microstructural characteristics are analyzed. and the resulting art piece is presented.

In high-pressure cold spray, the enthalpy of the particle carrier gas has a significant effect on the propellant gas conditions and ultimately on particle impact velocities and temperatures. Through modelling and experimentation, the current work demonstrates that in low-pressure cold spray, the particle carrier gas enthalpy has a minimal effect on the particle velocity and is rather limited to affecting the particle impact temperature. Consequently, particle impact temperature can be controlled independently from impact velocity. This is a valuable tool when dealing with temperature sensitive substrates: low propellant temperatures can be used in combination with high particle temperatures enabling particle deformation while minimizing substrate heat input. Particle preheating was used to inject pure aluminum particles in a commercial low-pressure cold spray to temperatures up to 500°C. This was accomplished without clogging because of the development of a novel particle preheater, which eliminated the particles exposure to hot metal surfaces. Even after substantial spray time, no evidence of wear or clogging was found. The particle preheating resulted in a deposition efficiency increase of 3.6 times when compared to the injection of room temperature particles.

Fluorinated polymer coatings are potential candidates for ice protection systems. The current work aims to develop such coatings using cold spray as a production method. A computational approach is used to design a new cold spray nozzle for the efficient deposition of adhesive perfluoroalkoxy alkane. The icephobicity of as-sprayed coatings are evaluated using three-fold characterization: surface’s wetting behavior, time-lapse study of water droplets freezing, and ice adhesion at both macro and microscopic levels. While the as-sprayed coatings exhibited sought superhydrophobic properties, their behavior changed when exposed to frost formation resulting in degraded wetting behaviors and much larger ice adhesion strength. This demonstrates the importance of frost formation when studying icephobic coatings.

The development of efficient ice mitigation systems for surfaces exposed to atmospheric ice has been in progress for decades. The need for passive anti-icing systems is essential as current ice mitigation systems require a substantial amount of energy and their implementation involves complex manufacturing considerations. Fluorinated polymer coatings are among the candidates for passive anti-icing systems. While many processes have been investigated to produce them, these methods can be costly, time consuming and can cause thermal damage to the substrate. The current work aims to explore a green and cheap alternative approach by using cold spray. Furthermore, the cold spray process offers advantages such as being a portable easy to perform solid-state coating process for eventual repairs. This work uses computational and experimental approaches to design and test a new dedicated nozzle for the efficient deposition of adhesive perfluoroalkoxy alkane. Computational results reveal that for the same operating conditions, the use of the new nozzle design increases particle impact temperature, improving the deposition of the feedstock material, as confirmed experimentally. The wetting behaviour, ice nucleation time and ice adhesion strength were compared for 6 different surface types, including bare aluminum, various polymer materials and the cold spray perfluoroalkoxy alkane coating on aluminium substrate. Results indicate that the as-sprayed coating performs as both a superhydrophobic and icephobic surface.

Titanium dioxide (TiO 2 ) coatings possess high appeal due to self-cleaning properties that can accelerate decomposition of organic pollutants. The global objective is to develop a cold sprayable feedstock powder with an outer titanium dioxide shell that maximises anatase-rutile heterojunctions for enhanced photocatalytic activity under ultraviolet light and the development of cold spray process parameters for successful deposition of this powder into thin photocatalytic coatings. The objective of this reported first step of our global research effort to produce superior photocatalytic TiO 2 coatings by cold spray is to successfully engineer anatase and rutile nanostructure heterojunction shells on pure titanium (CP-Ti) powder known to be easily sprayable by cold spray and then verify its photocatalytic properties through exposure to an organic pollutant, methylene blue (MB). Anatase and rutile heterojunctions are desired due to high activity, stability and broadened bandwidth as opposed to each singular nanostructure. The resulting powder coming out of this first step was characterized using Raman spectroscopy to verify the presence of the desired heterojunctions. The photocatalytic reactivity was tested and evaluated through the degradation of methylene blue upon contact with the TiO 2 powder. Results of this first step showed growth of desired heterojunctions and high reactivity of the produced powder.

This present work investigates the effect of electromagnetic fields on cold spray processes by means of an induction-heating cold spray (IHCS) system. Aluminum powder was cold sprayed onto inductively heated Ti6Al-4V (Ti64) substrates. These materials were selected to minimize the mechanical contribution to coating adhesion. As a result, changes in coating adhesion strength can be attributed to improved metallic bond formation due to the effect of the electromagnetic field. Four different initial substrate surface temperatures were used in the study to assess the role of initial temperature as well. Deposition efficiency and adhesion and tensile strength measurements were recorded and are used to characterize the hybrid coating process and compare it with traditional techniques.

Segregating the convoluted effects of particle size, impact temperature and velocity on deposition behavior and adhesion is of utmost interest to the cold spray field. The current study aims to associate the particle impact behavior and adhesion to its in-flight characteristics by studying and decoupling the influence of particle size, temperature and velocity for single particle impacts and full coatings. Experimental results reveal that in-situ peening processes contribute to the adhesion at low impact temperature while particle velocity controls the adhesion/cohesion at increased particle impact temperatures. The benefits of both bonding mechanisms are discussed in terms of measured adhesion/cohesion, bend-to-break fracture surfaces, pseudoplasticity, deposition efficiency and critical velocity. Computational fluid dynamics (CFD) results provide individual particle trajectory, size, temperature and velocity, of successfully deposited particles, which have led to the observed signs of metallurgical bonding.

As a result of the rise in processing power demands of today’s personal computers, water cooled pin fin heat sinks are increasingly being employed for the cooling of graphical processing units. Currently, these high performance devices are manufactured through high-cost, high-waste processes. In recent years, a new solution has emerged using the cold gas dynamic spray process, in which pin fins are directly manufactured onto a base plate by spraying metallic powder particles through a mask. This process allows for a high degree of adaptability to different graphics processing unit shapes and sizes not achievable by any other process to date. One drawback of this new additive manufacturing process is reduced deposition efficiency, resulting in a fair portion of the feedstock powder being wasted as substrate sensitivity to heat and mechanical residual stresses requires the use of reduced spray parameters. This work aims to demonstrate the feasibility of using powder recycling to mitigate this issue and compares coatings sprayed with reclaimed powder to their counterparts sprayed with as-received powder. In so doing, cold gas dynamic spray is shown to be a highly flexible and economically competitive process for the production of pin fin heat sinks even when spray parameters result in reduced deposition efficiency.

The cold gas dynamic spraying process solves many issues with respect to the deposition and additive manufacturing of metals. Namely, it provides a reduced reactive environment, simplicity of operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive in many situations and commercially available helium recovery systems constitute a major capital investment on top of the spray system and ancillary equipment. This work focuses on the development and use of a novel, inline gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios were investigated through particle velocity, deposition efficiency, porosity, and hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and that helium percentage can be optimized to reduce the overall coating production costs. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen-helium ratio that will produce the lowest overall coating cost.

This study investigates the effect of nozzle material on cold sprayed aluminum coatings produced using a downstream lateral injection system. It is shown through experimentation that nozzle material has a significant impact on deposition efficiency and particle velocity. It is proposed that the effects are related to complex interactions between particles and internal nozzle walls. The results obtained lead to the conclusion that nozzles with higher thermal diffusivity transfer more heat to particles when they make contact with internal surfaces, which increases deposition efficiency even though particle velocities are reduced.

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.

This study demonstrates a new approach for producing thick copper coatings on steel by cold spraying via nitrogen gas. To overcome delamination problems without resorting to helium, substrate surfaces are treated prior to deposition using a forced-pulse waterjet. Samples with different levels of roughness were prepared using both conventional and waterjet surface treatments. The samples were then coated with thick Cu using only N 2 and adhesion tests were performed. Test results show good coating adhesion on all waterjet treated substrates with bond strengths ranging from approximately 25 MPa to 58 MPa, depending on surface roughness. Consistent with previous studies, cold spray Cu did not adhere to any substrates that had been polished or grit blasted. It is shown that the pulsed waterjet creates a surface with anchoring features that interlock with incoming particles to form a strong mechanical bond.

This work studies the thermal and hydrodynamic performances of pyramidal fin arrays produced using the cold spray process as an additive manufacturing process. Near-net shaped pyramidal fin arrays of various materials were manufactured (pure aluminum, pure nickel and stainless steel 304). Fin array characterization such as fin porosity level and surface roughness evaluation was performed. The nickel pyramidal fin array is shown to be rougher compared to the two other materials used in this study. The results obtained show a lower thermal efficiency for stainless steel 304 whereas the performances of the aluminum and nickel fin arrays are similar. The multi-material sample has a better thermal efficiency than stainless steel 304, which constitutes the proof of concept of using a streamwise anisotropic fin array.

Ion vapor deposition is a physical vapor deposition process often used to apply pure aluminum coatings to aerospace parts for corrosion protection. These coatings, however, are vulnerable to damage during manufacturing and use, leaving the underlying material susceptible to corrosion. The aim of this study is to develop an economical and practical technique for the repair and restoration of damaged aluminum IVD coatings using available cold gas dynamic spraying equipment. Based on the porosity, surface finish, adhesion strength, and corrosion performance of the repair coatings, cold gas spraying is shown to be a strong candidate for restoring damaged aluminum coatings on aerospace parts.

This work studies the manufacturability of pyramidal fin arrays produced using cold gas dynamic spraying. Near-net shape pyramidal fins of various sizes were formed and tested. The fin arrays were characterized and their heat transfer properties were assessed. Results obtained correlate well with data published for banks of tubes at a similar dimensionless pitch, and show that fins produced by cold spraying outperform traditional straight-cut fins at the same fin density.

A model of the shock-wave induced spray process (SISP) and the criteria for bonding are used to predict whether particles traveling within the unsteady flow regime will adhere to the substrate upon impact. The results are then used to predict if a coating can be formed under specific spraying conditions. Having been validated based on particle velocity measurements, the model is used to investigate the effect of varying spray parameters, such as powder and gas initial temperature, gas heater length, and spray frequency.

Computational Fluid Dynamics (CFD) is used to model the Shock-wave Induced Spray Process (SISP). SISP utilizes the kinetic and thermal energy induced by a moving shock-wave to accelerate and heat powder particles, similar to Cold Gas-Dynamic Spraying (CGDS), where the particles impact the substrate and deform plastically to produce a coating. Individual powder particles reach the substrate at different velocities and temperatures depending on their location within the unsteady flow regime. The critical velocity correlated to particle impact temperature and a CFD model are used to predict whether a particle traveling within this unsteady flow regime will bond to the substrate upon impact or bounce off. This information is then used to predict if a coating can be formed under a specific set of spray conditions.

The recent development of cold spray technology has made possible the deposition of low porosity and oxide-free coatings with good adhesion and with almost no microstructure change of the coated parts. This work focuses on the performance of low pressure cold spray (LPCS) in repairing damaged Al-based thin aircraft skin. The coating quality is investigated through the evaluation of microstructure, microhardness, adhesion strength, surface finish and corrosion resistance of the coatings.

Microstructure and mechanical properties of 7075 Al alloy matrix and SiC reinforced composite coatings deposited on a T6 6061 Al alloy by cold spray are investigated. Feedstocks are prepared as mixtures of 7075 Al alloy and SiC powders with SiC content varying between 0 to 40 vol. %. Microstructural characterization is carried out by optical and scanning electron microscopic examinations and X-ray diffraction (XRD) analysis. The coatings mechanical behavior is evaluated using hardness measurements and wear tests. Wear tests are conducted under dry conditions using a ball-on disc tester under atmospheric conditions. The presence of SiC improves the coatings hardness and wear resistance when compared to pure 7075 Al coatings. The coating hardness increases with increasing SiC content; however SiC content higher than 10 vol.% does not lead to further increase in wear resistance. In this respect, the optimum composition of the coating is determined to be 92 vol. % 7075 Al + 8 vol. % SiC.

This work compares the oxidation behaviour of CoNiCrAlY coatings manufactured by the HVOF, APS and CGDS processes when submitted to temperatures of 1000°C and 1100°C. The as-sprayed coating microstructural features were characterised using SEM and XRD analysis before being subjected to isothermal heat treatments in an air furnace. Oxide scale composition was determined using XRD, SEM and EDS analysis while the oxide growth rates were obtained using mass gain measurements. The as-sprayed HVOF and CGDS coatings exhibit similar microstructures while the APS samples have a significantly higher porosity and oxide content levels. Results from the oxidation experiments indicated that the oxide growth rate of HVOF and CGDS were lower than that of the APS samples. The results also indicated that samples oxidised at 1100°C have a lower oxide growth rate than those oxidised at 1000°C. Analysis of the oxidation process up to 100 hours indicates that the formation of dense α-Al 2 O 3 is more favourable at 1100°C while a transition alumina, θ-Al 2 O 3 is more favourable at 1000°C. Furthermore, the surface profile of the samples oxidised at 1100°C were more uniform and free of protrusions.