Zinc oxide (ZnO) is known for its rich diversity of microstructures and has been attracting attention for its unique combination of mechanical and physical properties. It has been a material of interest in different areas such as optoelectronics, sensors and the general ceramic industry. It also has been a material of interest in biomedicine due to its antimicrobial characteristics and biocompatibility properties. A simple processing route to produce ZnO micro/nanostructures is the thermal oxidation of zinc, which results in a wide range of ZnO nanostructures depending on the oxidation conditions. The main objective of this study was to investigate the influence of a severe plastically deformed zinc microstructure on the formation of ZnO nanostructures produced by oxidation, with a special attention to the zinc oxide growth mechanism and nanostructures characteristics. For this purpose, the cold spray process was used to produce Zn coatings using different feedstock powders that required different process parameters in order to obtain Zn coatings with severely deformed particles. A non-catalytic thermal oxidation method was then used to successfully produce ZnO nanostructures at the surface of the heavily deformed cold sprayed Zn coatings. The as-grown ZnO nanostructures were investigated in detail using scanning electron microscopy and X-ray photoelectron spectroscopy. These investigations revealed that the chemical fingerprint of the oxides grown in the cold sprayed samples was different from that of conventional ZnO. It was also observed that in the oxidized cold sprayed Zn coatings, the formation of ZnO nanowires was hindered due to the formation of blisters generated during the high temperature exposure, revealing nonoptimized process parameters.

The hot-section components of modern gas turbines (e.g., turbine blades and vanes) are typically manufactured from Ni-base superalloys. To develop the γ/γ' microstructure that imparts superior thermomechanical and creep properties, Ni-base superalloys usually require three distinct heat treatments: first a solution heat treatment, followed by primary aging, and finally secondary aging. To achieve oxidation resistance, MCrAlY coatings are applied on the superalloy components as either environmental coatings or bond coats for thermal barrier coatings. In this study, the effects of different processing sequences on MCrAlY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically, cold spray deposition of NiCoCrAlTaY coatings was carried out on single-crystal Ni-base superalloy substrates that underwent various degrees of the full heat treatments prior to being coated. The remaining required heat treatments for the superalloy substrates were then performed on the coated samples after the cold spray deposition. The microstructures of the CMSX-4 substrates and NiCoCrAlTaY coatings were characterized after each heat treatment. Isothermal oxidation performance of the coated samples prepared using different sequences was evaluated at 1100°C for 2 hours. The results suggested a promising procedure of performing only solution heat treatment on the superalloy substrate before coating deposition and then primary aging and secondary aging on the coated samples. This processing sequence could potentially improve the oxidation performance of MCrAlY coatings, as the aging processes can be used to effectively homogenize coating microstructure and promote a thin thermally grown oxide (TGO) scale prior to actual isothermal oxidation.

In this study, a new physically-based finite element approach is proposed to model and predict the superficial oxide layer removal and the occurrence of localized metallic bonding during particle impacts. The process physics, based on explosive welding theory and experiments, and method implementation is presented. Prediction of critical velocity of copper is obtained and compared to experimental data to validate the model. Moreover, the model is also able to show the bonding locations at the interface between particles and substrate. The predicted bonding locations are consistent with experimental data from literature for several metals.

Metal surface characteristics play a significant role in interacting with their biological environment. Copper surfaces have been identified for their antimicrobial properties. Improvement of antibacterial and antiviral performances can be tailored by surface microstructure modification. Severe plastic deformation is an effective surface modification procedure to improve the mechanical performance of metal surfaces. This technique can be adapted to obtain surface grain refinement and induce surface roughness. In this work, cold spray shot peening is used to modify copper substrate surfaces and study the effects on their antibacterial properties. To modify the grain structure of copper, different shot-peening parameters were examined. The surface roughness and microstructure were investigated by employing optical and scanning electron microscopy. The bactericidal activity of copper substrates after shot peening treatment is discussed and a comparison between the bacterial load on treated (shot-peened surface and cold sprayed copper coating) and untreated surfaces (as-received) is provided. Testing of the surfaces after their exposure to the biological environment demonstrated improved microbial inactivation performances for surfaces that had undergone grain refinement without exceeding a certain roughness value.

In this work, a new cold-spray shot-peening process was used to achieve surface nanocrystallization on a magnesium alloy deposit. The results of various examinations and tests show that nanocrystalline layers up to 40 µm thick with an average grain size in range of 50-80 nm can be prepared on AZ91D deposits using the new process. The nanocrystalline layers also exhibit good microhardness and tribological properties.

In this study, nitrogen is employed rather than helium to cold spray MCrAlY coatings at relatively low process settings. Recycling of the non-deposited particles during the spray is also explored, and the characteristics and cold sprayability of recycled powder are compared with that of as-received feedstock powder. The resulting MCrAlY coatings from the two powders, though different thicknesses, show similar dense microstructures, low oxide inclusion, and smooth surface finish, all of which contribute to improved oxidation behavior.

This study assesses the viability of using nitrogen instead of helium to cold spray NiCoCrAlTaY coatings onto single-crystal superalloy substrates. The process, though feasible, has a low deposition efficiency, leading to a high level of deformation that affects the microstructure of both the coating and substrate. SEM and TEM analysis revealed metallurgical and mechanical bonding at the interface and grain refinement in the coating. A fine grain structure that developed in the substrate after deposition was also observed possibly caused by dynamic recrystallization during the deposition process. Evidence of element segregation in the substrate, identifiable as zones with a deformed γ/γ’ structure, was found as well.