Low pressure cold spraying is an attractive technique for onsite metal coating fabrication due to its compactness and portability. However, the bonding strength of the coating prepared by low pressure cold spraying is generally low, which restricts the further applications in engineering and industrial fields. To improve the bonding strength, pre-treatment on substrate surface can be an effective procedure. In this study, a low-temperature plasma treatment was applied to a pretreatment technique, and the effect of the treatment on particle bonding was compared with that of a laser treatment. Copper coatings on aluminum and copper substrates were selected and studied as basic metal materials. The SEM observation results show that the particle adhesion rate significantly increases by the laser and plasma treatments, due to the removal of the native oxide films on the substrates. The particle bonding on the plasma-treated substrate reveals better interfacial adhesion with less gap compared with the laser-treated one. The pre-treatment by low-temperature plasma can be an attractive technique to assist the cold spraying process due to the oxide removal ability and no thermal effect which can apply a wide range of materials.

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.

As steam power plants continue to move towards higher operating temperatures in order to improve efficiency, materials exposed to the working fluid are subjected to accelerated degradations in the forms of surface oxidation and reduced mechanical properties. In this study, the oxidation behavior of two cobalt base alloys, CoCrMoSi (T14) and CoCrNiMoSi (T19), was evaluated in superheated steam (SHS, 0.1MPa) at 800 °C for up to 500 hours. After the exposure, both T14 and T19 alloys experienced weight gain caused by oxidation. Visual observation and SEM surface analysis revealed that T19 had greater extent of surface oxide spallation than that seen on T14. From the cross-sectional evaluation, however, a thin, adherent oxide layer was found to have formed on T19. T14 in fact had suffered from excessive internal oxidation and the surface oxide was uneven. Based on the results obtained so far, it is believed that the finer Laves phase combined with greater amount of Cr in alloy T19 have enabled the formation of a protective oxide layer and thus reduced the extent of internal oxidation. Due to the extensive oxidation ingress along the large Laves phase, it is concluded that T14 is not suitable for applications in SHS at 800 °C.

Cold spraying is a semi-empirical method in that spray parameters must be optimized experimentally in regard to coating quality and deposition efficiency. In this work, porosity and deposition efficiency are the key parameters in the optimization of corrosion-resistant zinc coatings produced by high-pressure cold spraying. The deposition process is described along with the tests used to assess the morphology, adhesion, and anticorrosion properties of the coatings obtained.

Despite the wide application of powder metallurgy in the field of additive manufacturing, a general understanding of the spreadability of powder particles in electron beam powder bed fusion (EB-PBF) is lacking. This paper presents the results of a literature review on particle flowability and spreading in additive processes. Different flowability tests are described and spreading mechanisms for different powder-bed processes are reviewed. A technique is proposed to study spreadability in which a single layer of powder is ‘frozen’ in the as-spread condition by contact sintering and then characterized using white-light interferometry. A standard method to calculate powder-bed density is defined based on this approach, and correlations between density, packing factor, and flowability are established.

Non-destructive eddy current evaluation is a practical and well-established tool in aerospace and other industries, used to find or identify material defects not otherwise detectable. It can also be employed to measure the thickness of various coatings, although it is not yet fully optimized for multi-layer thermal spray systems, such as thermal barrier coatings (TBCs). The first part of this paper aims to look at the underlying mechanisms of the eddy current thickness measurement technique and uses a Design of Experiment (DoE) study to identify key characteristics related to thickness measurement of thermal barrier coatings. The second part of the paper is a case study on the application of the findings into general production, showing the achieved improvements in accuracy and repeatability of thickness measurements.

In this investigation, high carbon steel wire is deposited on aluminum cylinder bores with different surface profiles by plasma transferred wire arc (PTWA) spraying. The first part of the study deals with feedstock materials, process parameters, droplet formation, and splat morphology. The second part deals with bead profiles, build rates, and the influence of substrate composition, temperature, and surface profile on coating characteristics including microstructure, morphology, composition, and bond strength.

In this study, atmospheric and suspension plasma spraying are used to create nickel-based electrodes with enhanced surface area as required for hydrogen production. Optimal spraying conditions were determined using a Taguchi design-of-experiments approach. Electrochemical double-layer capacitance measurements by cyclic voltammetry show that suspension plasma spray coatings have more surface area than coatings produced by atmospheric plasma spraying. SEM micrographs show that the surface microstructure of the sample with the largest surface area contains high amounts of cauliflower-like aggregates with an average diameter of 10 µm. In general, the combination of melted, semi-melted, and resolidified particles leads to the formation of deposits with high porosity, rougher surfaces, and consequently larger surface areas.

This work evaluates the tribological properties of conventional and nanostructured Al 2 O 3 -13TiO 2 coatings obtained by atmospheric plasma spraying. The structure and composition of the composite coatings and powders were analyzed by SEM, TEM, and x-ray diffraction. Nanoindentation and ball-on-disc tests were conducted and surface topography was examined by noncontact 3D profiling. Coating samples of both types were polished and their friction coefficients were measured. The coefficient of friction for nanostructured coatings was 0.51, while that of conventional coatings was 0.62.

This work investigates the reliability and reproducibility of scratch testing for YSZ and TiO 2 coatings deposited on NiCr bondcoats by plasma spraying. Scratch tests were conducted on cross-sections of the spray coatings. An image of the scratched area was taken after testing using an optical microscope in order to determine failure mode. With a statistical evaluation, the adhesion and cohesion strength were determined. The results show that cross-sectional scratch testing is effective for estimating the adhesion and cohesion strength of plasma spray coatings.

In this study, dense yttria coatings are produced by conventional flame spraying using a yttrium ethylene diamine tetra acetic acid (Y-EDTA) complex as the feedstock powder. By adjusting spray parameters, the organic components in the EDTA are completely decomposed and only crystalline Y 2 O 3 phases are found in the deposits. Compared to atmospheric plasma sprayed Y 2 O 3 , Y-EDTA coatings produced by reactive flame spraying have better surface morphologies with fewer microcracks and are obtained at lower cost.

Titanium oxide coatings were suspension plasma sprayed onto different substrates. The suspension was formulated using fine rutile pigment in the mixture of water with ethanol. The zeta potential of the suspension was determined. The spray process parameters were designed using a full factorial plan using spray distance and torch scan velocity as the variables. The temperature at spray process was monitored using a pyrometer. The X-ray diffraction (XRD) analysis enabled to find out the crystalline phases in sprayed deposits and, in particular, the anatase content. Scanning electron microscope (SEM) enabled to characterize the coatings’ microstructure. The coatings included well molten lamellas and zones of loosely agglomerated and sintered grains. The scratch test of the coatings enabled to determine their mechanical properties such as critical load and scratch hardness.

Plasma sprayed ceramic coatings have been widely applied in modifying surface properties of metal components. They are useful to prevent various types of wear, corrosion, erosion and thermal degradation, thereby extending components service life and reducing the need for expensive and repetitive maintenance. The durability and functionality of plasma sprayed ceramic coatings is critically dependent on the adhesion between the ceramic coating and the underlying substrate as well as the cohesion between splats. In this work, both nanostructured and conventional Al 2 O 3 coatings were prepared by atmospheric plasma spraying technology (APS). For each feedstock, four kinds of coating samples deposited under different spraying parameters were designed, and moreover, seven groups of conventional coatings with different thickness were deposited under the same spraying parameters. Adhesion/cohesion of the plasma sprayed Al 2 O 3 coating samples were evaluated by scratch testing. The results obtained reveal that the spraying parameters have strong influences on the microstructure of plasma sprayed Al 2 O 3 coatings, which in turn influence their properties including deposition efficiency, porosity, microhardness as well as adhesion/cohesion.

Abradable coatings are located on the stationary parts of gas turbines, in front of blades, which cut a track in them. This has to be achieved with minimum wear of the blades, in order to control the over-tip leakage. These coatings are generally deposited by thermal spraying of composite powders comprising a metal base, a polymer filler generating porosities and a dislocator such as hBN. The very demanding properties are nowadays adjusted using rig tests, where samples are rubbed by the contact of a dummy, simulating actual working conditions in an aircraft engine. Several types of behaviour are usually described, but few numerical data are produced from these tests. Only the blade wear (or metal transfer) is generally measured. As the understanding of contact phenomena is fundamental for the development of predictive models allowing the design of more performing materials, a comprehensive characterization process of the rub path was developed. The study was based on a topological survey made by laser profilometry, giving three-dimensional maps. These maps were then processed by image analysis and several parameters were computed, like surface roughness and parameters giving information on the shape and orientation of the holes or grooves in the rubbed surface of the samples.

Controlled scratch testing, dry abrasion tests and hardness measurements were performed on WC-12Co coatings produced by the high velocity oxy-fuel spraying of nanostructured and conventional feedstock powders. The information obtained employing these different evaluation techniques was used to provide insight into coating behaviour and identify the most abrasion-resistant coatings. The results indicated a correlation between scratch hardness and the microhardness determined by Vickers indentation for the coatings. There was good agreement between the scratch test and the abrasion test in identifying the best coatings for use in dry abrasion. Observation of the scratched surfaces and wear scars indicated material removal by splat debonding and fracture. The results demonstrate the usefulness of the scratch test for assessing the abrasion resistance and wear behaviour of coatings.

The appropriate selection of bulk materials and coatings of valve components, is an important factor for the economic success of oil and gas production activities in petrochemical field. Materials and coatings are important because particle erosion and surface wear is associated to corrosion by hydrogen sulphide during oil and gas flow. The wear of high pressure valves of gas system will lead to pollution, safety problem and cost increases. The most popular solution of these problems is the deposition of hard material like tungsten carbide or chromium carbide by thermal spray. Particularly these coatings are deposed by HVOF (High Velocity Oxygen Fuel) to obtain a very high hardness with excellent cohesion and adhesion. Tungsten carbide cobalt-chromium based coating, chromium carbide nickel-chromium coating as well as Inconel 625 are adopted actually in the specifications of the industrial petrochemical companies and their behavior and wear, erosion and corrosion properties are reported in literature. This paper addresses the study and surface analysis and characterization of alternative coatings such as NiAl and composite material WC / intermetallic compounds containing mainly Ni, Cr, Co and Mo. The best parameters to produce these coatings has been found by implementing a DOE and the obtained coatings have been systematically submitted to corrosion and functional tests based on the determination of the behaviour of the thermal spray coatings in an atmosphere of H 2 S and CO 2 [1] and to wear and erosion test according to ASTM G75-95; removed material weight and usured surface damages have been determined. Furthermore the coatings have been completely characterized before and after the tests from the point of view of the structure (porosity, coating cohesion and adhesion, hardness, wear) and of the surface properties by means of a prototype 3- dimensional stylus micro-topography surface analysis system. Their corrosion and functional behaviour have been finally compared with the behaviour of the above mentioned coatings applied at present as standard in the petrochemical sector. The results state that WC/intermetallic compound could be a good substitute of IN625 for certain kind of application where good antierosion behaviour is requested.

This paper explores the effect of bond coat processes and surface characteristics on the failure mechanism of thermal barrier coatings (TBC's). TBC's consist of a 300µm thick air plasma sprayed (APS) top coating of ZrO 2 -8Y 2 O 3 w% and CoNiCrAlY bond coats which were deposited using low pressure plasma spray (LPPS), shrouded air plasma spray (SPAS) and high velocity oxy-fuel (HVOF) combustion spray and different size powder. Bond coat surface profiles were measured by profilometric techniques and surface roughness was calculated according to the measured results. TBC performance and failure mechanisms were evaluated by adhesive bond strength testing, image analysis measurements of porosity, thermal cycling testing. X-ray diffraction and microstructural analyses. Research results show that bond coat deposition processes and surface characteristics had significant effects on the thermal cycling lifetime and failure mechanism.

This work examines nanocrystalline thermal spray coatings prepared under several power and stand off distances. The coating material was nanocrystalline alumina + titania and zirconia (ATZ) powder mixture deposited using an air plasma spray process. The experimental design employs a full factorial method totaling four samples. The mechanical properties of four coatings were compared via scratch and hardness testing. The scratching process was monitored for transverse loads during the test and the variation in load monitored. The profiles of scratches were analyzed using white light interference profilometry and studied further via SEM. The results indicate that the microstructure reflected features observed in the scratch test. It was also shown that the scratch process and morphology depend on the normal load and spray process.

This paper compares the wear properties of HVOF-sprayed WC/12Co hardcoatings produced from different powder feedstock materials, including conventional, nanophase, and mixed powders. The mixed or multimodal feed powder is designed to minimize the amount of material that goes through a high temperature cycle during spraying, thus potentially limiting the extent of decarburization in the resulting coating. As will be shown, decarburization is indeed minimal in a multimodal coating, which translates into exceptional resistance to abrasive and sliding wear. Another favorable factor is the ability to increase the volume fraction of hard WC phase in such a coating, thereby further enhancing its wear resistance.

Adhesion of ceramic coatings considerably depends on the surface characteristics of blasted substrates. The roughened surfaces have two kinds of topographical characteristics, one is of their cross section and the other is of planar. The roughened surfaces is generated by angled grit-blasting process which can be expected to improve the adhesion of ceramic coatings. The topography of the roughened surfaces has fractal characteristics in their cross section and has been more effectively related to the adhesive strength of ceramic coatings than average surface roughness traditionally used. This paper presents that fractal characteristics is evaluated in the planar topography of the blasted surfaces and shows that the planar fractal characteristics is closely related adhesion of ceramic coatings. The planar fractal dimension is evaluated by SIA (Slit Island Analysis) which needs the height data on the roughened surface. Those data are obtained by a laser-microscope in confocal type.