In conventional powder processing, there has been considerable work on classifying feedstock powders based on particle size distribution, morphology, microstructure and composition, since these influence processability and final properties. Cold spray is a new application for powders and conventional characterization may be insufficient to assess powder cold sprayability. In particular, metallic powders have an oxide layer, which breaks during impact with the substrate or with another coating layer during cold spray; this fragmentation facilitates bonding. It has been suggested that the thickness of the oxide layer can influence the mechanism of fragmentation; thicker oxides are easier to remove, revealing clean metal surfaces that can metallurgically bond. Consequently, not all high-purity powders or powders that are stored in ambient conditions have the potential to give good coating properties after cold-spray. This work focuses on surface oxidation of the powders, characterizing the variation of oxide film aspects with size and composition of nominally pure copper powders using X-ray Photoelectron Spectroscopy (XPS). The results indicate the presence of Cu (I) and Cu (II) oxide species on the surface of as-received, naturally aged and heat-treated powders; their thickness is determined using the depth profiling feature.

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.

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.

In a cold spray technique (CS), which used for making dense and thick metallic coatings, the fine solid metallic particles are impinged and deposited on a substrate at subsonic or supersonic velocity. The property and performance of a CS metallic coating significantly depends on the bonding state of particle-substrate and particle-particle interfaces. Therefore, the deposition mechanism of the CS particles has become one of the most important research targets. However, it is difficult to experimentally evaluate the deposition mechanism due to numerous impingements of very fine particles with various size and shape. In this study, in order to evaluate the deposition mechanism, a CS emulated environment was created by a single particle shot system (SPSS) in which spherical particle with 1 mm diameter is impinged on a substrate. The influence of substrate surface oxide film on deposition behavior of a spherical Al particle with 1 mm diameter was investigated. The thickness of surface oxide film on a substrate was controlled by heat treatment and estimated by X-ray photoelectron spectroscopy (XPS). Using the SPSS, Al particles were impinged on the substrates with different surface oxide film thicknesses. The critical velocity, which means the starting velocity for particle deposition, and the microstructure of deposited particle were evaluated. From the results, it was found that the surface oxide films on substrates play important roles on the deposition behavior of the Al particle.

Cavitation erosion frequently occurs in hydraulic components such as turbines, valves, pumps, and ship propellers. Arc thermal spray processing has the possibility to be used for maintenance recovering of hydraulic blade runners. Fe-Cr-Mn-Si is a cavitation-resistant class of steel with a high concentration of oxidation elements—which can be important for arc thermally sprayed coatings—and a strain-induced phase transformation. The influence of chemical composition on oxide formation, microstructure, and cavitation resistance of Fe- Mn-Cr-Si thermally sprayed coatings was studied, and its field performance in a Francis type runner was evaluated. Microstructures and properties were investigated by XPS, XRD, optical microscopy, and ultrasonic cavitation testing. The best cavitation resistance was obtained in Fe-Mn-Cr-Si alloy with a nickel addition; this composition has lower oxide and splash droplets content and exhibits better splat wetting than Fe-Mn-Cr-Si without nickel. Strain-induced phase transformation occurred in arc thermally sprayed coatings during cavitation tests. Better performances for Fe-Mn-Cr-Si alloys, without nickel, were obtained in alloys with higher strain induced martensite contents after cavitation tests. In field tests, after 2000 operation hours, it was verified that the recovered areas presented only a small number of eroded areas, and cavitation erosion was reduced compared with uncoated areas.

Coatings of poly(ether-ether-ketone) (PEEK) have been produced using the high-velocity air fuel (HVAF) thermal spray technique. These coatings have been produced at 50 and 100 mm nozzle lengths and 200, 300, and 400 mm gun-to-substrate distances on stainless steel 304 substrates. The techniques used to characterize and determine the extent of thermal degradation of the PEEK coatings were valence-band XPS and FTIR-ATR. Valence-band XPS showed that, in general, minimal degradation of the PEEK occurred during the HVAF thermal spraying process. FTIR-ATR results showed that more surface degradation of the PEEK coating occurred at the 200 mm gun-to-substrate distance for both nozzle lengths than at the larger gun-to-substrate distances. Specifically, absorption bands appeared at 2918 and 2850 cm -1 , which correspond to alkane –CH 2 – asymmetric stretching modes. The resolution of the 672 cm -1 peak, which corresponds to C–H vibrations on the phenyl ring, increased from one to two peaks in the spectra of the 200 and 300 mm gun-to-substrate runs. This indicates a structural change in the phenyl ring, possibly indicating a change in the extent of crystallization of the PEEK polymer.

The powders of Bi 2 O 3 and Bi 2 WO 6 were prepared by calcination, sintering and crushing. Their sizes were screened out to be in the range from 50 to 150 µm. The initial spray parameters were optimised using numerical codes simulating the behaviour of powders in plasma jet. Spray experiments onto metallic substrates were carried out using commercial plasma torch SG-100, equipped in an external powder injector. The spraying of coatings was carried out by varying electric power input to plasma, distance of spraying and the geometry of injector. The morphology of sprayed coatings was investigated using scanning electron microscope (SEM). X-ray Diffraction (XRD) of Bi 2 O 3 coatings revealed the α-Bi 2 O 3 phase, present in the initial powder, and also β-Bi 2 O 3 in some of the samples. Reduction of oxide into metallic Bi at spraying process was not discovered using XRD and Differential Thermal Analysis (DTA). Bi 2 WO 6 powder was crystallized in an orthorhombic phase that transformed into tetragonal one at spraying. Finally, the X-ray Photoelectric Spectroscopy (XPS) investigations revealed a possible presence of Bi(OH)3 phase in the coatings sprayed using Bi 2 O 3 powder.

In the thermal spraying of powder materials, it has been observed in practice that the splat shape changes to a disk type from a splash type with increases in the substrate temperature. However, the details of the substrate surface change due to the heating has not been fully characterized. In this study, an AISI 304 stainless steel substrate surface heated to 673K was analyzed precisely by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The results obtained revealed that the change of the substrate surface occurred not in the chemical composition but mainly in the surface roughness, especially surface morphology in nano-meter scale. Hence, substrate heating may bring about the change in substrate surface and this change induces the transition phenomenon.

Thermal barrier coating failures almost always occur by spallation due to interlayer stresses. During service, a thermally grown oxide forms between the bond coat and insulating ceramic. This oxide has a significant impact on the life of the coating. In this work, a number of innovative methods are used to study TBC bond coats, topcoats, and interface oxide layers. CoNiCrAlY bond coats produced by APS, VPS, and HVOF spraying are analyzed by X-ray photoelectron spectroscopy (XPS) and compared based on the presence of oxides. Zirconia powders and topcoat layers are examined by X-ray diffraction and Raman scattering in order to study the crystal structure and spatial distribution of different phases. The authors also use Raman microscopy to map the surface of the topcoat layer and XPS to determine the elemental composition. This provides useful data because surface and interface roughness affect the spallation resistance of the oxide layer and thus the expected life of the TBC. Paper includes a German-language abstract.

This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

The isothermal and cyclic oxidation of freestanding Ni-20Cr-10Al-lY thick coatings has been investigated at 1200°C using TGA, SEM, XRD and XPS techniques. Coatings produced by HVOF are dense and remain crack free after thermal treatments. The protective oxide layer formed did not flake off upon cyclic oxidation as confirmed by SEM analysis. In addition, three oxidation regimes were identified after analyzing TGA data: two below 1000 °C and a third one at approximately 1200°C. The regimes below 1000°C correspond to the selective oxidation of elements on the surface and at the subsurface of the coatings whereas the third regime involves element diffusion from the bulk of the coating to the surface. The oxidation regime became asymptotic at 1200 °C as stable oxides formed. The presence of water vapor affects neither the thickness nor the orientation of oxide crystals formed on the surface as confirmed by the X-ray analysis. The XPS and X-ray results show an inter-diffusion between the coating and substrate with a slight increase in chromium concentration at the interface. Element distribution within the oxide layer was found to follow the order: Al-(oxide)Y-(oxide)/Cr-(oxide)/Ni-(oxide)/NiCrAlY from the outermost oxide layer to the bulk of the coating. These results show that HVOF dense Ni-20Cr-10Al-lY sprayed coatings can be used as anti-oxidant barriers in both isothermal and cyclic oxidation at 1200°C.

The quasi-steady magneto-plasma-dynamic (MPD) arcjet generator is a promising plasma accelerator, which has a coaxial electrode structure similar to those of conventional plasma torches. The MPD arcjet generator utilizes principally electromagnetic acceleration of the interaction between the discharge current of kiloamperes and the azimuthal magnetic field induced by the discharge current, although the working gas is accelerated aerodynamically through a nozzle in a thermal arcjet generator. In this paper, ablation-type MPD arcjet generators are developed for ceramic coatings. Discharge voltages and ablation rates of ceramic materials are examined, and front velocities of ablated atoms of ceramic component are also estimated using a streak camera. The Vickers hardness of coating is measured. Their cross sections are observed with a scanning electron microscope, and their surfaces are analyzed by means of x-ray diffraction and x-ray photoelectron spectroscopy. Paper includes a German-language abstract.

The decomposition of bioactive plasma sprayed apatite layers and the weakness of their interface with the metallic substrate limit the longevity of orthopaedic prostheses. Analysis of the coating and of the metal-apatite interface using EDS, XPS, and IR techniques indicates alterations of the apatite composition which can be related to several chemical reactions occurring either in the plasma or on the surface of the implant. EDS shows a calcium-rich layer on the apatite side of the interface whereas after dissolution of the apatite, XPS indicates that phosphorus atoms are incorporated in the metal surface. Depending on the rate of decomposition, calcium oxide may possibly form and weaken the apatite-metal interface. Fluorohydroxyapatite coating have proven to decompose less and differently and to be more effective than hydroxyapatite coatings.