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.

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.

In this work, amorphous Zr-based bulk metallic glass deposit was manufactured by cold spray. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition or rebound. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposit, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of interface, and high gas-temperature induced partial melting of particles and resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass particles, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed metallic glass.

Wear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/Co powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by microindentation and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis are used to investigate the phase retention. Fine nanocrystalline WC-structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental coatings exhibit high hardness values in the range of the commercial ultrafine carbide WC reference. The novel nano-structured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.

Yttria stabilized zirconia with a composition of ZrO 2 -8wt%Y 2 O 2 typically serves as the topcoat in thermal barrier coating systems. It has been reported, however, that YSZ with lower yttria content is more resistant to thermal shock and the effects of high-temperature sintering. To investigate these reports, nano-agglomerated 5YSZ and 8YSZ powders were deposited on FeCrAl substrates by atmospheric plasma spraying and the coatings were heat treated at 1400 °C for 1, 5, and 20 h. The nanostructure content in the 5YSZ samples was found to be about 20% higher, the microhardness 11% lower, and the size of unmelted particles about 27% smaller, which shows that bimodal structured 5YSZ has higher sintering resistance than traditionally used 8YSZ.

Cation-deficient perovskite-type oxides have received considerable attention as new thermal barrier coating materials because of their extremely low thermal conductivities. In this study, sintered samples produced from RTa 3 O 9 (R: Y, La or Yb) powders are examined and the mechanisms behind their low thermal conductivity are investigated. Thermal conductivity was found to vary primarily with the ionic radius of the R element. As ionic radius decreases, nanodomains form via tilting of the TaO 6 octahedra. Phonon scattering at the domain boundaries is thus likely responsible for the low thermal conductivity of cation-deficient perovskite oxides.

In this study, copper-doped bimodal WC-Co powders are applied to steel substrates by high-velocity oxyfuel spraying and the coatings are evaluated based on their microstructure and high-temperature wear performance. It is shown that the addition of copper reduces coating porosity without affecting the structure of the WC. It also inhibits the decomposition of WC and has a solid diffusion function. The friction coefficients and wear rates determined at different temperatures were found to be consistently low with minimum values being obtained at 450 °C. At high temperatures, the soft copper flows to the surface, forming a self-lubricating film that reduces friction and wear.

In this study, pure rutile TiO 2 coatings are deposited on stainless steel substrates by very low-pressure plasma spraying (VLPPS). The spraying system was used in the reactive mode, injecting both titanium powder and oxygen gas to achieve nanosize particles. Optical emission spectroscopy showed that the interaction between Ti particles and O 2 occurred in flight. Coating microstructure and phase composition were characterized at the surface and in the bulk with respect to operating parameters. Coating surfaces show typical cauliflower microstructure with many nanoparticles, while the microstructure below was found to change from binary to columnar as spraying distance increases.

The agglomeration process plays an important role in suspension plasma spraying (SPS), affecting the state of particles prior to impact and consequently the mechanical properties of the coated substrate. This paper presents the results of an investigation on the agglomeration of submicron YSZ particles sprayed from a water suspension. The shape and surface morphology of transient and final agglomerate structures was studied by injecting YSZ suspensions with a nebulizer into an inductively coupled plasma torch. It was found that particle agglomeration occurs in successive stages identified as cup or doughnut shaped agglomerates, polycrystalline particles, and amorphous or partially molten particles.

This study shows how HVOF-sprayed NiAl coatings produced using chemical and electrochemical activation processes can serve as oxygen evolution electrodes in alkaline water electrolysis systems. Freestanding hierarchical NiAl structures produced without chemical binders exhibit electrocatalytic performance comparable to state-of-the-art noble catalysts characterized by very low overpotential and high current density without degradation.

Dense, nanostructured bismuth vanadate thin films were successfully deposited by aerosol deposition at room temperature. Aerosol deposition offers an alternative route for fabrication of photoactive metal oxide coatings as no binders or sintering processes are employed. A micron-sized bismuth vanadate powder was used to spray photoactive films (< 1 µm) on conductive fluor-doped tin oxide layers on glass and titanium substrates. The thin films are photocatalytically active under solar light due to the band gap energies of bismuth vanadate, and their nanosized structure increases surface area and catalytic activity. The coatings obtained were assessed based on microstructure, layer thickness, mechanical integrity, and photoelectrochemical activity.

Single component tin coatings have been successfully cold-sprayed onto carbon fiber reinforced polymers. Coatings with mixed metal powders have also been sprayed to improve conductivity for lightning strike protection purposes. Test results indicate a noticeable improvement in deposition efficiency with the addition of a secondary metallic powder. This study examines the effect of aluminum powder additions in tin coatings. Following cold spraying of various Sn-Al mixtures over a wide range of gas pressures, unusual coating morphologies were observed. The study of these morphologies reveals two distinct deposition phases depending on spray pressure. The presence of submicron particles also supports the occurrence of a powder melting phenomenon during the spraying process.

In this work, binder-free Co 3 O 4 films with in-situ oxygen vacancies are deposited in a one-step process by solution precursor plasma spraying (SPPS). It is believed to the first time Co 3 O 4 layers composed of hexagonal flakes were synthesized through the SPPS route. Specific capacitances up to 1700 F/g were obtained at a scan rate of 5 mV/sec, almost 97% of which was retained after 13,000 cycles at 20 mV/sec. This supercapacitor-like performance is attributed to the synergistic effects of a binder-free composition with in-situ oxygen vacancies and porous nanostructures.

Wear and corrosion of aircraft actuator parts and helicopter gearbox rotating shafts and also wear of seals working against these parts can lead to oil leaks, which require expensive maintenance and increase the risk of failure. The Hardide nanostructured Chemical Vapor Deposition (CVD) Tungsten Carbide coating can help reduce oil leakage from gearboxes and actuators and increase maintenance intervals. The coating protects metal pistons and shafts from abrasion and corrosion, keeping their surface roughness parameters within optimum ranges for longer; this reduces seal wear and makes the whole unit more durable and reliable. The 50-100 microns thick CVD Hardide coating can be applied uniformly on internal and external surfaces and has enhanced fatigue and anti-galling properties. The coating has enhanced wear resistance outperforming Hard Chrome by 14 times and Thermal Spray WC-Co (12%) by 3 times. The fine-grain coating nanostructure wears uniformly so even worn Hardide coating shows no hard micro-grain asperities which are abrasive for seals. The coating is free from porosity and from Cobalt binder and is an excellent barrier against corrosion. As a result the coating keeps the optimal seal-friendly surface finish for longer even in abrasive and corrosive environments. The coating was qualified by Airbus as an environmentally-friendly replacement for Hard Chrome plating.

Magnesium light weight alloys are currently being studied as implants due to their biodegradability. However, its applications are limited by high rate hydrogen evolution during corrosion. Coating on this substrate is one of the ways to reduce the rate of corrosion and increase the life of this type of implant. Hence, hydroxyapatite (HA) was coated on the substrates by using high velocity oxy- fuel (HVOF) spraying. The main purpose of such coatings is increasing bioactivity as well as corrosion resistance of the Mg alloy. Crystal structure was characterized by X-ray diffraction (XRD). Crystallinity of the coating was about 70% in which HA is dominant phase. The amounts of hydrogen gas released during magnesium corrosion tests in simulated body fluid (SBF) were measured to evaluate the corrosion resistance of the coated samples. This coating could decrease hydrogen evolution from 100 per cm 2 .mL to about 15 per cm 2 .mL after 29h of immersion time.

This study was focused on the biocidal efficacy on spores of copper alloy sheet and copper alloy coating at two different surface topographies. Endospores can remain viable in a dormant state for centuries. Our work compares the effectiveness of copper alloy coating and copper sheet metal in killing endospores. A twin-wire arc spray system was used for coating of stainless steel coupons. The feedstock was CuNiZn wire, the coating thickness was 400 µm. The copper alloy sheet metal had the same composition and is registered as antimicrobial by Environmental Protection Agency (US). Uncoated stainless steel coupons were used as controls in all experiments. The surface was polished to two roughness levels: Ra=3.5 µm and Ra=0.1 µm. The surface topography was analyzed by a stylus profilometer and 3D image analysis. EDS and FIB were used to characterize the elemental composition and structure of flower-like nanostructures and endospores. The results obtained in this study indicated that changes in Ra values of 0.1 and 3.5 µm had no significant impact on the biocidal activity of sheet metal and the coating on E. coli , S. epidermidis and B. subtilis . The coating was as effective as the EPA-certified sheet metal in the destruction of vegetative cells within 5 minutes. This study indicates that degradation of B. subtilis endospore begins within 2 hours after exposure to the coating. By day seven, only extensively degraded endospores and nanostructures were visible on both surfaces. Our results show that thermal spray copper alloy coatings were as effective as certified antimicrobial sheet metal in the destruction of endospores within hours; however, the coating was more effective in killing the endospores after one week of exposure.

Tungsten carbide -based hard metal coatings are extensively used in demanding industrial applications like for wear protection purposes. Continuously increasing demands set new limits and need for materials with enhanced features. One solution is to improve hard metal properties by nanostructures. Presented study is part of a research where novel and safe route to manufacture nanostructural WC-Co powders starting from water soluble raw materials was developed. In this study powders’ workability in thermal sprayings is studied. WC-12Co powder was manufactured using water soluble raw materials: ammonium metatungstate as a tungsten source, glycine as a carbon source and cobalt acetate as a cobalt source. The powder was manufactured via optimized spray drying and heat treatment method producing a correct phase structure and chemical composition. Experimental powder was sprayed by HVAF-spraying to study its workability and functionality. Morphology, microstructure and properties were analyzed from the experimental nanostructural powder and the HVAF-coatings.

There have been increasing demands for adequate gas sensors to monitor O 3 , a respiratory irritant gas associated with a spectrum of adverse health events. Here we report film construction by liquid flame spray route and characterization of nanostructured WO 3 -reduced graphene oxide (rGO) composites and their gas-sensing activities to O 3 . The starting feedstock was prepared from WCl 6 and rGO for pyrolysis synthesis by flame spray. Nanosized WO 3 grains exhibited oriented nucleation on rGO flakes and rGO retained intact nano-structural features after the spraying. Constrained grain growth of WO 3 was realized in the rGO-containing films with 60-70 nm size as compared to ~220 nm in the pure WO 3 film. The WO 3 -rGO film sensors showed quicker response to O 3 and faster recovery than the rGO-free WO 3 film sensors. Addition of rGO in 1.0wt.% or 3.0wt.% in the films caused significantly reduced effective working temperature of the film sensors from ~250°C to ~150°C. These results might shed some light on liquid flame spray fabrication of novel functional nanocomposites for gas-sensing applications.

Properties and performance of the coating fabricated by wire arc spray process strongly depend on various factors including spray parameters and characteristics of both in-flight particle and splat. In this study, relationship between in-flight particle, splat formation and microstructure of the CrMoBW-Fe based nanocomposite coating fabricated by wire arc spray process were investigated. The Focus ion beam (FIB) milling was used to prepare a transversal cross-section of the in-flight particle and splat to be characterized by scanning electron microscopy (SEM) along with an energy dispersive x-ray spectroscopy (SEM-EDS). In addition, phase compositions were also analyzed by using x-ray diffractometer (XRD). The results revealed that size of the in-flight particles and splat morphology greatly influenced microstructure and properties of the coatings. In-flight particles were revealed a spherical-shape with a broad size distribution ranging from 0.8 to 115 µm at the average of 26 µm particle diameter. In-flight particles were well flattened on impact giving flower-shape splat with the average diameter of 100 µm. Flattening degree was found to be 3.8. Arc sprayed CrMoBW-Fe base nanocomposite coating showed very thin splat with fine lamella structure which implied that particles were fully molten upon impact onto substrate.

In the current work, Ni-20Cr coatings have been developed for potential use in harsh environments of power plant boilers. A pre-synthesized Ni-20Cr nanocrystalline powder was deposited on T22 boiler steel using cold-spray process. The high temperature oxidation behavior of the coating was investigated under cyclic conditions at 900° C for 50 cycles, so as to understand the kinetics of oxidation. Moreover, high temperature erosion-corrosion (E-C) behaviour of the coating was ascertained under cyclic conditions in an actual boiler at 740 ± 10°C for 1500 hours. The oxidized and eroded-corroded samples were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses. The microhardness, oxidation and E-C data for the developed coating was compared with an earlier reported cold-spray Ni-20Cr coating, which was developed by using a commercially available micron-sized Ni-20Cr powder. The results showed that the developed coating was found to have 33% high microhardness in comparison with the microstructured Ni-20Cr coating. The oxidation and E-C rates of the steel were found to decrease significantly after the application of the developed coating by 89% and 68% respectively. Moreover the nanostructured coating outperformed the corresponding micro-structured Ni- 20Cr coating with regard to high temperature oxidation and E-C resistance to boiler steel by a significant fraction. The investigated coating was found to have oxidation protective oxides such as Cr 2 O 3 and NiO in its oxide scale and was found to be spallation-free.