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.

Large pure aluminum powders were deposited on as cast-, T4- and T6-AZ91D magnesium substrates using cold spray. Heat treatment was applied to the coated components under vacuum at 400°C for different holding time. The effects of the heat treatment on the microstructure as well as the coating/substrate adhesion strength were investigated. Thick (~ 400µm) and dense (<1% porosity) Al coatings have been obtained on the three different substrates. During heat treatment, Mg 17 Al 12 (β) and Al 3 Mg 2 (γ) intermetallic phases were formed at the Al/Mg interface and the thickness of the intermetallics layers increased with the holding time. No significant thickness difference of the intermetallics layers were observed on as cast- and T6-AZ91D substrates, while thicker layers took place on the T4- substrate. It is believed that the higher Al concentration within the T4-AZ91D material could be beneficial for intermetallic growth because less enrichment is required to reach the critical level for intermetallic formation in the substrate. Shear strength tests were performed on the as sprayed and after heat treatment coatings. The results revealed lower adhesion strength in the samples after heat treatment than the as sprayed ones which is attributed to the presence of brittle intermetallics layers at the coating/substrate interface.

The objective of this work is to demonstrate the ability of the Pulsed Gas Dynamic Spraying process (also known as Shockwave Induced Spraying) to produce nanostructured metal matrix composite. Nanocrystalline and microcrystalline (conventional) Al5356+20%B 4 C composite feedstock powders were used. The influence of the coating process as well as the nature of the feedstock material on the microstructure and mechanical properties of the coatings were studied. The new spraying process provides an opportunity to produce hard and dense coatings with good cohesion between deformed particles and good adhesion to the substrate. No phase degradation, low compressive residual stresses and high dry sliding wear resistance were observed which seem to be an advantage compared to the traditional thermal spray coatings.

This paper examines the oxidation behaviour of CoNiCrAlY coatings manufactured by APS, HVOF and CGDS deposition techniques when subjected to isothermal heat treatments. Comparison of the as-deposited coating microstructures is achieved by means of scanning electron microscopy (SEM). Investigation of the oxide compositions and growth dynamics is achieved by SEM, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxide growth rates were determined by a series of mass gain measurements. Results from this study demonstrate that lower coating porosity and oxide contents lead to lower oxide growth rates. Results also demonstrate that low-temperature processing of CoNiCrAlY bond coats is beneficial to their oxidation behaviour as it favours the formation of alumina in preference to other detrimental fast-growing mixed oxides.

The work presented in this paper is part of a comprehensive research program aimed at exploring the possible use of pulsed gas dynamic spraying to produce WC-based coatings. This portion of the work assesses the effect of processing parameters on particle characteristics and coating microstructure. Particle velocity is measured at the gun exit using a laser diagnostic system and correlated with various spray parameters. A combination of analysis techniques (OM, SEM, XRD, and microhardness) are used to characterize the feedstock powder and sprayed coatings. The results show that an increase in particle preheating temperature and velocity increases hardness and reduces coating defects.

This study is part of an ongoing effort to develop high performance CoNiCrAlY bond coats by means of cold gas dynamic spraying in order to have complete control of bond coat microstructure. As such, the objective of the work presented in this paper is to perform a detailed analysis of cold sprayed CoNiCrAlY layers to assess any changes in microstructure, relative to the original feedstock powder, that may have occurred during layer build-up and compaction. Based on SEM, TEM, and XRD examination results, it is shown that, contrary to the generally accepted theory, important microstructural changes occur during the cold spray deposition process. In the coating samples examined, investigators observed evidence of grain refinement in the CoNiCr γ-phase matrix and partial dissolution of NiAl β-phase precipitates. These changes are a result of severe plastic deformation due to the high-velocity impact of sprayed particles.

The present work probes the deposition of metallic coatings on high fiber volume fraction carbon/epoxy polymer matrix composites using pulsed gas dynamic spraying. Well-consolidated and well-adhered coatings of zinc and copper were successfully applied and initial trials with higher melting point metals have been promising. Two key aspects of the technique are the low temperatures involved and the presence of embedded ductile particles in the substrate. The embedded particles promote adhesion and eliminate the need for surface preparation procedures along with associated risks. The hardness and porosity of the zinc coatings deposited on polymer matrix composites were found to be comparable to that of similar coatings on metallic substrates.

The aim of this work is to assess the ability of pulsed gas dynamic spraying to deposit coatings on the inside surface of cylindrical workpieces. Thick dense copper coatings are produced on flat surfaces and on the inner surface of cylindrical workpieces using a specially designed gun extension. The coatings are evaluated based on microstructure and microhardness in order to determine if the copper has the same characteristics on all surfaces. A comparison between pulsed gas and cold gas dynamic sprayed copper coatings is also presented.

Aluminum-based composite coatings reinforced with different volume fractions of SiC particles were deposited on aluminum substrates by means of pulsed gas dynamic spraying using a mechanically mixed composite feedstock powder. Microstructural features of the coatings are examined and their hardness is reported. The results show that the high fraction of SiC particles in the feedstock powder are retained in the coatings and that increasing SiC content in the aluminum matrix significantly improves coating hardness. The highest hardness value was obtained for a coating with 28 vol% SiC. Beyond that, coating hardness decreased, which is attributed to increasing porosity and decreasing cohesion between deposited aluminum-based particles.

Due to their mechanical properties, WC-based cermet coatings are extensively used in industrial wear-resistant applications. These coatings are usually prepared using thermal spray processes. However, due to the nature/environment of the spraying processes, the feedstock powder structure and properties suffer from severe decomposition, which subsequently degrade the performance of the coatings produced. The cold spray process appears to be a promising process alternative to preserve the properties of the feedstock powder during the coating preparation. Although, the later technique can eliminate or minimize the degradation of the material, the deposition of cermet is a complex process. In this study, nanocrystalline WC-15Co and conventional WC- 10Co4Cr coatings were deposited using both the continuous and the pulsed cold spray processes. Microstructures of the feedstock powders and the coated layers were investigated by OM, SEM and XRD. The results revealed the possibility of depositing cermet coatings onto aluminum substrates by both processes without any degradation of the phase composition of the feedstock powder. However, the continuous process experienced difficulty in depositing and building up dense coatings without major defects. Meanwhile, the new pulsed process revealed the capacity of depositing thick cermet (conventional and nanocrystalline) coatings with low porosity as long as the feedstock powder was preheated above 573 K.

A new process, the Pulsed-Cold Gas Dynamic Spraying process is presented in this work. A description of the process and of the experimental set-up developed at the University of Ottawa Cold Spray Laboratory is presented. It is envisioned that this process could allow for the feedstock particles to be accelerated to high impact velocities and intermediate temperatures, in a non-reacting gas. That way, the intermediate particle impact temperature would lead to a lower critical velocity as compared with CGDS that could be easily reached while preserving the chemical and microstructural composition of the feedstock particles in the coating. Selected examples of the variety of coatings produced with the system are presented, illustrating the potential of the process to deposit various materials as well as its main benefits.