The effect of martensitic phase transformation on cavitation erosion resistance for a deposited layer prepared from a Fe-8Cr- C-1.5Al-Ti flux-cored wire of metastable steel was studied. A reference material of AISI 316L stainless steel was used as a substrate. Cavitation tests were performed using a modified ultrasonic tester. X-ray diffraction was used to examine the phase transformation before and after cavitation tests. Also, the eroded surfaces of specimens were investigated by optical microscope (OM), scanning electron microscope (SEM), and 3D optical profilometer. The cavitation results revealed that the deposited layer exhibited a resistance to cavitation erosion approximately 10 times higher than the AISI 316L steel due to the martensitic phase transformation occurring during the cavitation process. The phase transformation plays a main role to minimize the cavitation damage of specimen. This is due to the fact that it contributes to obstructing movement of dislocations and increasing the hardness as a result of the increased hardening on the surface.

Binary spinel-type metal oxides (AB 2 O 4 ) semiconductors, including ferrites (AFe 2 O 4 ), are attractive photocatalysts thanks to their excellent visible light response and good photochemical activity and stability for the photodegradation of organic pollutants. Currently, their synthesis proceeds via conventional chemical routes that follow rather tedious protocols and the final preparations consist in nano-powders, a form that is not exempt of EHS (Environment, health and safety) risks along their handling. From an industry perspective, it is desirable to dispose of an efficient and preferably simple synthesis route capable to produce photocatalytic preparations in a non-dispersible form, for instance in the form of robust films attached on solid substrates. We report herein a single-step method based on the Solution Precursor Plasma Spray (SPPS) process that enables the preparation of promisingly active ferrite-based photocatalytic films, namely CuFe 2 O 4 and ZnFe 2 O 4 . We have investigated various types of precursor solutions, including the atomic A/Fe ratios, solvent type and solute concentration, and studied the evolution of the phase composition of the resultant CuFe 2 O 4 and ZnFe 2 O 4 films by XRD. The corresponding surface morphologies and energy bandgaps were also studied by SEM and UV-Vis spectroscopy, respectively. Then the photocatalytic activities of the selective ferrite films were evaluated through the degradation of aqueous solutions of the Orange II dye under different light irradiations. The results of the overall work also revealed that SPPS process represents a fast, one-step, versatile alternative compared to conventional multi-step processes, which is suitable for preparing complex composition metal oxide film-formed photocatalyst.

The powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

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.

Thermal spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. A selective enrichment of the surface layer region with carbon by means of thermochemical heat treatment improves the residual stresses and increases the wear resistance. The interstitial deposition of carbon causes strong compressive residual stresses and a high surface hardness. The low process temperature of the thermochemical heat treatment avoids the precipitation of chromium carbide, whereas the corrosion resistance is not affected. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial carbon enrichment of the thermal spray coating is possible. In comparative studies between carburized and untreated thermal spray coatings, the influence of the carbon enrichment on the coating properties and the microstructure was investigated. Carburized coatings demonstrate a significant improvement in adhesive wear resistance and an extremely high surface hardness. The cross section micrograph of the carburized coating shows the S-phase formation in the surface layer region. The depth profile of the carbon concentration was determined by GDOS analysis.

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.

Conventional processes of gas shielded metal arc welding (GMAW) do not offer directly the possibility for cladding heat sensitive materials such as aluminum with iron-based materials due to intermetallic Al/Fe phases form. This paper deals with the first evaluated cladding results of aluminum components with iron-based nanocrystalline solidifying materials by controlled shielded metal arc welding processes to improve wear resistance. In the present work, the design of experiments and data evaluations are systematically applied to get the first results about the dependence between controlled arc welding process parameters and the iron-based coatings of aluminum substrate. In particular, the effect of the chosen parameters such as wire feed speed, welding speed, frequency and further factors on the heat input, welding penetration, micro hardness, rate of welding penetration and width of intermetallic phases in the interface zone are investigated. Optical and scanning electron spectroscopy provide input for further statistical evaluation. The experiments were carried out using various controlled arc technologies which offer different control over the heat input to the substrates. Different power supplies were used.

In this study, agglomerated nanocrystalline ZrO 2 --Y 2 O 3 powder was calcinated from 900 to 1300 °C for 2 h. The calcinated nanopowder was used as feedstock and deposited by air plasma spraying on a NiCoCr bond coat applied to a nickel substrate via low pressure plasma spraying. For comparison, conventional ZrO 2 -Y 2 O 3 topcoats were also produced. Nanostructured and conventional thermal barrier coatings were calcinated from 1050 to 1250 °C for 2-20 h. Experimental results indicate that monoclinic tetragonal phases in the agglomerated nanopowder were transformed into cubic phase after calcination. The cubic phase content increased with increasing calcination temperature. High temperature calcination can make the yttria segregated at grain boundaries dissolve in zirconia. Different from the phase constituent of the as-sprayed conventional TBC, which consisted of diffusionless transformed tetragonal, the as-sprayed nanostructured TBC consisted of cubic phase containing high yttria. No phase transformations were observed in either TBC after calcination.

In this study, the deposition, microstructure, and resistivity of APS and HVOF sprayed Cr 2 O 3 -TiO 2 coatings is systematically investigated. Commercially available Cr 2 O 3 -rich feedstock powders are used along with five agglomerated and sintered experimental powders on the TiO 2 -rich side. Both processes are found to produce homogeneous, low-porosity coatings with phase compositions that can be changed by adjusting process parameters. Coating hardness and electrical resistivity are found to depend heavily on Cr 2 O 3 content.

Intermediate temperature solid oxide fuel cells include in their design a solid electrolyte layer, usually made of yttria-stabilized zirconia, that acts as an ionic conductor through which oxygen ions diffuse. This layer must be as thin as possible to limit ohmic losses yet have a low leakage rate corresponding to a low level of connected stacking defects such as microcracks. Suspension plasma spraying (SPS) appears to be a viable method for manufacturing such layers and is used in this study to produce gastight coatings that with further improvements may meet the requirements of SOFCs. The paper describes the setup and optimization of the SPS process and the methods used to evaluate the solid electrolyte layers.

Post-annealing of cold spray coatings has great potential for wear applications because it produces intermetallic compounds at low temperature far below equilibrium. This study investigates the effects of spraying pressure on the intermetallics formed and their dispersion characteristics. In the experiments, Al and Al-Ni powders were sprayed on Ni and Al substrates at 0.7, 1.5, and 2.5 MPa and a portion of the coating samples were annealed in argon at 500, 550, and 600 °C. Detailed examinations showed that Al particles are subject to peening effects that can interfere with the formation of intermetallic compounds during annealing, but that the effects can be mitigated by controlling gas pressure. Spraying pressure was also found to have an effect on the formation of eutectic pores in Al-Ni composite coatings, with higher pressures corresponding to fewer pores.

This paper presents a way of processing cold-sprayed Ti-Al to produce titanium aluminum nitride coatings. These coatings are meant to serve as a durable protective layer on tools exposed to molten aluminum alloys. A Ti-Al powder mixture with a weight ratio of 70/30 was cold sprayed onto specially prepared substrates using nitrogen as a process and powder delivery gas. The resulting coatings were alloyed at different temperatures to obtain a stabilized Ti-Al intermetallic phase for further nitriding treatment. The nitriding process was carried out in an ammonia-nitrogen atmosphere at 900 °C. The final product had a web-shaped microstructure with the same thickness as the cold-sprayed Ti-Al. Test samples were placed in molten aluminum for 1200 hours without notable chemical reaction.

This work shows that hydroxyapatite (HA) can be cold sprayed simultaneously with titanium to form thick biocompatible coatings without compromising the phase constituents of the bioceramic material. XRD analysis indicates that the phase composition of the HA in the deposit is identical to that of the powder. The work also shows that very dense Ti and Ti-HA composite coatings can be produced using sponge Ti powders and nitrogen process gas. The adhesion strength of the cold-sprayed Ti-HA exceeded the reported values of comparable plasma-sprayed coatings.

In this study, suspension plasma spraying is used to deposit pseudo eutectic alumina-yttria stabilized zirconia as a potential thermal barrier coating. Process variables including feed rate, powder size, and plasma gas composition were altered to determine the influence of spray parameters on the formation of phases in the composite coating. The most significant variable was found to be the auxiliary gas. The gas influences the formation of phases primarily through its effect on in-flight particle velocity.

Changes in phase composition of titania (TiO 2 ) coatings were studied with respect to in-flight particle characteristics during atmospheric plasma spraying. A CCD camera was used to record the average temperature and velocity of TiO 2 particles within the plasma jet for six combinations of spraying parameters selected according to Taguchi design of experiments. Phase composition of the coatings was assessed by means of X-ray diffractometry and numerically specified using Rietveld analysis. Changes in composition between the powders and coatings were observed with respect to the in-flight properties of the titania particles during spraying. In general, it was shown that the amount of impurity phases (hematite, quartz) present in the powder decreased after deposition and that in-flight temperature has only a moderate effect on the phase composition of TiO 2 coatings. For comparison purposes, additional coatings were deposited by cold spraying and phase composition changes were assessed.

Flame sprayed Al-12Si coatings were produced onto the surface of composite castings parts in order to enhance the adhesion of such castings. Due to the high surface roughness and the presence of pores in the coatings combined with the formation of an intermetallic phase at the interface, the adhesion of flame sprayed composite castings could be enhanced by a factor of 2 in comparison to blank castings and by a factor of 1.3 when compared to sand-blasted castings. However, results also show that gaps are mostly present at the interface between the Al profiles and the flame sprayed coatings and these gaps have a negative effect on the adhesion values of the composite casting parts. Therefore, an optimization of the adhesion of the coating on the Al profiles through an optimization of both the sand-blasting and the flame spraying parameters would be beneficial for further enhancement of the adhesion of composite casting parts.

The corrosion behavior of Al alloys, produced by cast and powder (Low Pressure Gas Dynamic Spray or Cold Spray) technologies, was examined in 3% sodium chloride solution from the viewpoint of localized corrosion. The susceptibility to localized corrosion is known to be strongly affected by intermetallic phases present in the alloy’s microstructure. The influence of individual cathodic and anodic intermetallic phases was investigated by using a microelectrochemical setup and by electrochemical methods. The optical and scanning electron microscopy data reveal that the cast and powdered alloys experience localized corrosion due to presence of the intermetallic phases which results in the micro-corrosion effects such as exfoliation corrosion, intergranular or crevice corrosion, and most severely pitting. Cast material has lower corrosion properties because of the higher heterogeneity of the structure as compared with powder sprayed composite.

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. New process equipment offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

High temperature fuel cells of SOFC type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced light-weight planar cells for electricity supply systems in cars and other mobile systems. Such cells, in one current design, consist mainly of metallic parts, e.g. of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of Cr-species from the inter-connect or the casing into the electrolyte/cathode interface forming insulating phases and the mutual diffusion of substrate and anode material, e.g. iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite which in both cases reduces performance and system lifetime. Protecting intermediate layers, can reduce such effects considerably if they are dense, stable and of high electronic conductivity. Perovskite-type layers (e.g. doped LaCrO 3 ) applied with high-velocity Direct Current-Vacuum Plasma Spraying (DCVPS) promise to solve reliably such problems.

Extensive research activities were conducted over the last few years on coatings made of titanium oxide, an established material for thermally sprayed coating solutions. Multiple existing and potential applications are closely connected with the existence of different titanium dioxide modifications and the formation of suboxides. This provides a basis for discussions on the Ti-O phase diagram as well as the properties and conditions of formation of relevant phases. Coating microstructures, phase compositions and mechanical properties are discussed as a result of interactions of different spray powders in different spray conditions of atmospheric and vacuum plasma spraying (APS and VPS), as well as of high-velocity oxyfuel (HVOF) spraying. The discussion on applications is focused on electrically conductive coatings, coatings with photocatalytic properties and coatings for wear applications.