Recently, laser deposition technologies have made significant advancements in their ability to manufacture high temperature metals and ceramics. One of these technologies, known as Direct Energy Deposition (DED), has the potential to deposit a wide range of materials from polymers to refractory materials, ceramics and functionally graded materials. This study evaluates major microstructural characteristics of WC-Co additively manufactured by DED technology. This material is commonly used for deposition of protective coatings due to its high hardness and excellent wear resistance. To this end, hardness and wear resistance of the DED processed samples were also investigated in this study. WC-Co coatings are generally deposited using various thermal spray technologies. However, it is speculated that DED deposited WC-Co could provide superior properties such as higher hardness and wear resistance. A DED manufactured WC-Co sample was examined by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Those studies could provide information about important microstructural features, chemical compositions and phase distribution. All the tests were also repeated on High-Velocity Oxygen Fuel (HVOF) deposited WC-Co with the same composition. Both DED and HVOF produced WC-Co coatings experience decomposition of the carbides into compound phases; however, the DED deposited sample displays unique dendritic and eutectic structures that improve the hardness and wear properties compared to the homogenous HVOF coating. In addition, DED produced samples show higher hardness and relatively better wear resistance compared to the HVOF deposited ones. The obtained results could establish a relationship between microstructural characteristics with hardness and wear properties of both samples.

Chemical leaching is proposed as a method to control porosity in stainless steel HVOF coatings. The leaching behavior is evaluated as a function of the stainless steel 444 and the pore former (Fe 3 Al) volume fractions and particle size distributions. The resulting porous structures are evaluated by optical microscopy. It was observed that the melting degree of the stainless steel splats was an important factor to retain some mechanical integrity after leaching. A discussion is presented to point out possible routes for the improvement of chemical leaching as a methodology for pore control in thermal spray coatings.

In the present study, a novel and practical method, white light interference, was proposed to characterize the lamellar pores covered by thermally sprayed YSZ and LZ splats. In this method, only an ordinary optical microscopy (OM) was employed. Colorful Newton rings and parabolic shapes of the lamellar pores were widely observed by OM. The crack spacing and the shapes of the lamellar pores captured by OM were well consistent with those by scanning electron microscopy (SEM) and focus ion beam (FIB). Besides, mechanical analyses were carried out and the results were well consistent with those by OM. Most importantly, the essential fact that the lamellar pores resulted from transverse cracking/delamination in thermal sprayings was highly elaborated.

Recently a Ti–TiAl 3 metal–intermetallic laminate (MIL) composite attracts growing attention because they have potential application in honeycomb or sandwich components of airplanes and as biomaterial with good bio-compatibility. Of the available processing techniques, diffusion bonding of elemental titanium and aluminum foils is an effective low-temperature method to synthesize the composite, allowing growth of the intermetallic layer. However, application of assembling and multi-pass cold rolling operations leads to fact that this technology is complex and expensive. The use of Cold Spray technology instead of aluminum foils utilization and multi-pass cold rolling to produce the Ti–TiAl 3 MIL composites is believed to be more effective. However, reaction diffusion kinetics of Ti-Al particulate composite differs from that of classical MIL composite and needs to be studied. The task of this paper is to define microstructural changes of Tl-TiAl 3 composite coating during cold spraying and reaction sintering. The optical microscopy, SEM, EDS, X-ray and microhardness examinations are presented and discussed.

Cold Spray is a material deposition process where the effects of substrate roughness on cratering phenomenon are often observed. In order to understand and explain crater formation on cold sprayed coatings, the laser surface texturing technique is used. This innovative process allows to control the substrate surface roughness and to create a controlled topography. In this study, five hole sizes from 20 to 100 μm diameters with an angle of 45° were drilled to obtain different working craters. Subsequent, build up of the coating was investigated. Aluminum powder and nitrogen were used for this study. The main gas temperature and pressure were respectively 500°C and 3MPa. The morphology and the microstructure of aluminum coatings were characterized by optical microscopy and scanning electron microscopy. Surface improperly filled crater affects bond strength. The objective is to determine the effect of surface morphology on craterisation weakening the bond strength. The erosion velocity creates locally a hydrodynamic penetration leading to strong erosion.

Ceramic coatings are applied in mechanical components subject to high temperature conditions, normally are deposited by plasma thermal spraying process. In this work, the porosity of YSZ ceramic coatings, deposited with different parameters conditions were analyzed by optical microscopy, scanning electron microscopy using back-scatter electron (SEM-BSE) detector and ultrasonic technique. It was verified that porosity measurement by optical and scanning electron microscopy is very sensitive with respect to metallographic preparation, mainly cutting process, and gray level adjustment. SEM-BSE technique showed less scatter results with easier porosity visualization, compared with optical microscopy. The porosity of the coatings was also measured by ultrasonic technique. It was observed that the ultrasonic velocity increase with porosity reduction. Ultrasound technique showed a good correlation with OM and SEM porosity measurement.

The rapid pace of advancement in thermal spraying is in large part due to the availability of diagnostic tools that are used to measure process variables such as particle temperature, particle trajectories, and plume geometry. The work presented here deals with the adaptation of an imaging method that can be used to visualize, quantify, and distinguish between laminar, transitional, and turbulent flow regimes. The method is based on schlieren photography and an image processing procedure that extracts the density field of a flow relative to a background image. In this study, the promising new method known as background-oriented schlieren (BOS) is used to evaluate different nozzle designs for twin-wire arc spraying. The results are presented and compared with CFD simulations, conventional schlieren images, and color photographs of the spray plume.

Since 2000, cast iron-liners have been replaced in several engine projects by Fe-based thermally sprayed coatings in the bores of a light metal crankcase. In contrast to cast in liners the linerless versions of these Al-crankcases are very demanding with regard to the porosity and tensile strength in the areas around the bores. The casting porosity has to be diminished to maximum pores smaller than 1mm² due to the roughening procedure, either mechanical roughening (MR) or high power water jet roughening (WR), in order to prevent either tool failure (MR) or widened pores (WR). At Nemak Dillingen these challenges are met by the Core Package Process (CPS), offering the advantages of a highly flexible casting design and a nearly unlimited choice of the cast alloy. These boundaries enable the production of lightweight crankcases made of the strong and creep resistant Al-Si-Cu based secondary alloy A319. The high quality of the cylinder bore surface is achieved by a carefully designed thermal household of the solidifying casting. The cylinder chill form a stable and sound shell in the very beginning of solidification, whereas feeding takes place from the sidewall structure of the crankcase. At the same time, specially designed chills for the bearing seat enable a very short solidification time, the resulting properties are crucial for highly loaded diesel engines. After casting and machining, the crankcases have been mechanically roughened and coated with 0.8 % C-Steel. The coatings and the interface between the coating and the casted Al-substrate have been investigated by means of light microscopy regarding the interlock between coating and substrate and the near-surface porosity of the cast metal.

In this study copper coatings were deposited by cold spraying, under different spraying conditions. Microstructure of the coatings was investigated by optical and scanning electron microscopy. Additionally, differential scanning calorimetry (DSC) and thermal gravimetric analysis were used to examine the quality of the coatings, especially with regards to the extent of the bonded area between the particles. The DCS results indicated exothermic reactions at certain temperatures, which revealed correlations with the spraying conditions and some of the observed microstructural features. In view of these results, it is concluded that thermal analysis can be utilized reliably to assess the quality of coatings, and in particular, to examine the fraction of bonded areas in cold-sprayed deposits.

Zinc coatings are widely adopted for cathodic corrosion protection. Mostly the process of choice is hot-dip galvanizing but due to limitations regarding component size and composition of the galvanizing bath it is not always practicable. In the present paper zinc coatings alloyed with Al, Sn, Mg and Cr are applied by twin wire arc spraying to enhance the corrosion protection ability of zinc thermal sprayed coatings. The alloys were characterized and investigated using salt spray test and by means of electrochemical corrosion. Corrosion damage and products were investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and electron probe microanalysis (EPMA).

Cavitation erosion is a common phenomenon that occurs in hydraulic turbine blades and result in mass loss. Welding is the most common technique used to recover the geometrical profile of these cavitation eroded turbine blades, however it is known that tensile residual stress can develop. The development of manufacture process that could reduce or eliminate the residual stress level will contribute for a longer service life of this component. It is aimed in this study evaluate cavitation erosion mechanism of Fe- Mn-Cr-Si-Ni arc thermally sprayed coating. Coatings were analyzed by optical and scanning electronic microscopy, microhardness, cavitation tests (ASTMG32-92) and the analysis of eroded surface areas after ultrasonic cavitation tests with DRX and SEM. The results showed that lamellae morphology, oxide volume fraction and porosity modified by changings in parameters deposition, modified cavitation mass loss mechanisms. After ultrasonic cavitation tests, it was verified that mass loss occurred by interlamellae oxide removal and splats surface deformation in initial stages, followed by rupture and finally detachment of the lamellae. Splashing droplets promote greater mass loss in some localized areas because they lower intersplat cohesion.

Magnesium coatings were deposited upon aluminum and stainless steel substrates by cold spraying. Three Mg powders with different particle size distributions were used as feedstock. The microstructures of as-sprayed coatings were evaluated by optical microscopy, and scanning electron microscopy. The coating observations show that a main gas temperature has an important effect on the deposition behaviour of particles. Changing the gas temperature from 350°C to 630°C involves an increase of the deposition efficiency from 1.57% to 19.57%. The effects of the particle size distribution and substrate material on the deposition efficiency of particles were also investigated. The results show that the particle size distribution has a significant effect on the deposition efficiency of particles which increases from 19.57% to 59% when the mean particle size decreases from 63 µm to 38 µm under gas temperature of 630°C. However, the deposition efficiency of particles was slightly influenced by the substrate material. In addition to these experimental results, the in-flight particle velocities were simulated by FLUENT software to point out the effects of the gas temperature and particle size distribution.

The adhesion mechanisms involved in the cold spray coatings are not still well elucidated. The quality of the deposit does depend mainly on particles and dynamic characteristics (which result from nozzle type, nozzle-substrate distance, etc.). The present work is based on the study of particle-substrate and particle-particle interfaces in the tantalum-copper coating-substrate system. The content focuses on the influence of the oxygen content in the starting powder on interface features, consequently on coating properties. Tantalum powders with different oxygen levels were studied using SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Microanalysis). Laser shock spallation of cold-sprayed Ta coatings was developed as a reliable and flexible process to achieve Ta spalls to be deposited at a high-velocity onto Cu targets. The velocity due to the laser shock could be controlled to be similar to that of particles in conventional cold spray. This results in Ta-Cu interfaces, the study of which was carried out to go into interface phenomena involved in cold spray, using TEM (Transmission Electron Microscopy) in particular. Results were compared to those obtained from laser shock spallation of Ta bulk specimens (i.e. made of a conventional Ta sheet). The role of powder oxidation on interface soundness was exhibited. Adhesion was shown to be all the lower as powder oxygen content was higher, using LASAT (“ Laser Shock Adhesion Test”) in addition to direct observation of interfaces. Results were exploited to discuss properties of the corresponding Ta coatings onto Cu, i.e. which were cold sprayed using powders with different oxygen contents.

Tungsten-based cermets are well-known engineering materials finding applications in aerospace, nuclear equipment, and many other fields. Plasma spraying is an interesting industrial process to manufacture those refractory materials. Original plasma sprayed hard coatings for wear protection composed of a stainless steel matrix and inclusions of tungsten carbide (WC) nanoparticles were developed. To built-up the coatings, two precursors were injected separately in the plasma jet : a stainless steel micrometric powder was classically injected into the plasma jet using a carrier gas whereas WC nanoparticles were injected with a liquid carrier, like in the so-called process suspension plasma spraying. One of the challenges is to maintain the WC phase stoichiometry in the deposit, without decomposing the carbide into brittle W 2 C, W 3 C, and metallic tungsten, phenomenon usually occurring with thermal spraying techniques. Another issue is to succeed in including homogeneously the carbide nanoparticles in a sufficiently dense stainless steel matrix. Coatings with different WC contents were deposited on stainless steel substrates and investigated with respect to their microstructure by optical and scanning electron microscopy, porosity level using the Archimedean method, phase composition by X-ray diffraction and Vickers micro-hardness. Results have shown that coatings consisting of a stainless steel matrix containing inclusions of carbide nanoparticles can be produced by plasma spraying. The phase composition analysis indicated that nanoparticles are largely composed of the WC phase and contain a small amount of WC1-x phases. A slight increase of the porosity level was measured for coatings containing nanoparticles, compared to the pure matrix, probably due to the cooling effect of the WC carrier liquid on the in-flight characteristics of the stainless steel particles. Micro-hardness measurements gave similar values for with or without nano-sized particles, showing that the amount of WC included in the samples was insufficient to improve the hardness property.

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.

Energy obtained by wind turbines can be foreseen to constitute a significant part of the future energy sources. A major challenge is however the large variation over time in wind energy production. Energy conversion from electricity to storable energy is therefore a key technology to master, and it is therefore important to develop compact, reliable, cheap and energy efficient equipment for this. An obvious solution is production of hydrogen based on water alkaline electrolysis. In the work presented the atmospheric plasma spraying (APS) of Raney nickel (50/50 Ni/Al) was used to develop electrodes with a large specific surface area as well as a considerable energy efficiency in high temperature water alkaline electrolysis. The coating process was analyzed using a plume analyzer as the primary tool and the coating properties were analyzed by a combination of bonding strength measurement, optical (OM) and scanning electron microscopy (SEM) as well as testing of the activated electrodes in a laboratory electrolysis cell. The results of the spraying process analysis are reported together with the electrochemical properties of the activated electrodes, and with regard to energy efficiency very positive results are obtained for the measured overvoltage.

In this work, the influence of the substrate temperature on the deposition efficiency and on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using CGT Kinetics 3000 deposition system. The substrate temperature was ranged between 20°C (room temperature) and 375 °C and was kept nearly constant during the deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within one minute from the deposition) and then characterized. The residual stress was determined by Almen gage method (Ref 1, 2, 3), Modified Layer Removal Method (Ref 4, 5, 6), and XRD (Ref 7) in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating- substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.

Silicon based coatings are showing great promise for power applications in the semiconductor, target, and solar industries. In order for thermal plasma spraying of silicon to continue to have an industrial impact in these industries, careful investigations into the deposition properties must be undertaken. We used a Thermach gun and powder feeder, to deposit silicon onto 100 mm x 50 mm x 1.6 mm steel samples. Coating cross-sectioning and image analysis was performed in order to evaluate the coating’s microstructure and porosity. Mechanical property measurements consisted of hardness testing on the coating cross sections. In addition, scanning electron microscopy and optical microscopy were conducted. These results combined for an analysis into the deposition properties of silicon coatings using various particle sizings, plasma power, and spray distances. Correlations between these input parameters and their effect on the microstructure are critical to semiconductor depositions of silicon.

Hypoeutectic AlSi engine blocks of modern passenger cars are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. A very promising alternative to the use of cylinder liners lies within the application of thermally sprayed coatings onto the walls of cylinder bores as friction partners for the piston rings. This work describes the development of a novel iron based wire feedstock as well as its application by the Plasma Transferred Wire Arc internal diameter coating system. The material developed within the frame of this work leads to partially amorphous coatings with embedded nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of Aluminium EN AW 6060 and onto cylinder bore walls of in-line 4 cylinder engines. All substrates were mechanically roughened in order to obtain high bond strengths of the sprayed coatings. The coatings microstructure was analysed by light optical microscopy, hardness measuring by transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.

Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.