Both as bulk material and coatings, cemented carbides currently occupy very well-established market niches and exhibit a promising future thanks to the development of compositions and manufacturing parameters. Direct comparisons of the properties of both are found only very rarely in the literature, very likely because the fields of application are complementary to each other but keep mostly separated. The current work is intended to evaluate similarities and differences in terms of microstructure and properties for two submicron WC-12 wt.%Co coatings obtained by High Velocity Air Fuel (HVAF) and Cold Gas Spray (CGS), together with a conventional sintered part. Microstructural features are discussed according to the inherent characteristics of each processing method. This covers a wide range in terms of the mechanical and thermal stresses acting on the material. While in CGS, the impacting particles do not melt, but experience extremely high plastic strain rates, the cobalt matrix is fully molten in the conventional sintering process, allowing time enough for diffusion processes. HVAF is to be placed in between, since the deposition process is characterized by a moderate heat input, leading to partial and/or full melting of cobalt, followed by rapid cooling. The microstructure and phases of the deposited coatings and bulk are characterized by using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Electron Backscattered Diffraction (EBSD) investigations enable local phase distribution of Co and WC in the samples. The hardness of the alloy processed by the three different routes is investigated as well. Additionally, electrochemical corrosion measurements in NaCl media are presented to evaluate the facility for electrolyte penetration and how the degradation of the material is affected by its inherent microstructure.

Cold Gas Spray (CGS) technology has allowed the development of biofunctional composite coatings composed of 45S5 and Polyetheretherketone (PEEK). The combination of a bioactive glass material embedded in a biocompatible polymeric matrix becomes this new composite in an interesting material for orthopedic applications since meet the biomechanical and biological requirements of an artificial implant. In the present study, blends of bioactive glass 45S5 and PEEK powder with different granulometry and 45S5/PEEK ratio have been prepared. These mixtures of powders have been deposited onto PEEK substrates by CGS with the goal of incorporating a bioactive additive to the biocompatible polymer, which can improve the bone-implant interaction of PEEK. The deposition efficiency (DE) and thickness of the coatings have been evaluated and from the results obtained, it was possible to conclude that DE and coating thickness are significantly affected by the granulometry and by the 45S5/PEEK ratio of the blends. By Scanning Electron Microscopy (SEM) inspection, it was observed that the use of blends with high 45S5/PEEK ratio led to the deposition of coatings with high content of 45S5 particles embedded in the polymeric matrix. Finally, the friction behavior of the coatings was analyzed performing ball-on-disk tests and these experiments showed that the presence of glass particles has a beneficial role in the wear resistance of the coatings.

A non-destructive inspection technique known as photoluminescence piezospectroscopy (PLPS) has been used to measure residual stresses in thermally grown oxide layers in TBCs subjected to thermal cycling at 1121 °C. YSZ topcoats were applied by atmospheric plasma spraying on cold-sprayed bond-coated Ni superalloy substrates. Residual stresses were analyzed as a function of thermal exposure. Changes in stress were used to indicate spallation and damage degree in the coating system.

Plasma sprayed thermal barrier coatings (TBCs) have been extensively employed in most aerospace and land based turbine engines, permitting gas temperatures to be raised substantially above those for uncoated systems. Traditional TBC systems are composed of a metallic bond coat and a ceramic top coat both applied by plasma spraying. New deposition techniques have been proposed mainly for the metallic bond coat, like high-velocity oxy-fuel (HVOF) and more recently cold gas spray (CGS). CGS is an attractive technology that generates very dense coatings, without oxidation and maintaining the initial powder microstructure, characteristics that are potentially interesting for bond coat application. In the current study, TBCs with two sets of cold gas sprayed bond coatings were prepared and evaluated in high temperature isothermal oxidation tests. Measurements of sample mass as well as microstructure observations were carried out on the as sprayed and oxidized samples to compare the behavior of different bond coat chemical compositions. As sprayed oxidation degree, structural changes and bonding strength of the samples were also determined.

The main objective of this study is to determine the optimum conditions for cold spraying a WC-Co nanopowder on aluminum alloy and carbon steel substrates. XRD tests were run on the powder and coatings to determine if phase changes occurred during spraying. Coating samples were evaluated via adhesion, corrosion, and wear testing. Cold spraying proved to be very competitive with conventional thermal spray techniques, producing thick, dense, hard WC-Co coatings on steel as well as aluminum with excellent tribological and electrochemical properties.

This study evaluates the corrosion and wear resistance of WC-Co coatings produced by cold gas and HVOF spraying. Three WC-Co cermet powders varying in cobalt content were deposited on aluminum alloy substrates by both methods. The powders were characterized based on microstructure, particle size distribution, and phase composition, and the coatings based on cross-sectional microstructure, phase composition, and Vickers hardness. The coatings are also compared based on the results of ball-on-disk, rubber-wheel, and electrochemical testing, which shows that CGS has several advantages over HVOF spraying for the deposition of WC-Co coatings.

In the present study, spherical Ti-6Al-4V powders were cold sprayed on titanium, aluminum, and magnesium alloy substrates to investigate influences over a wide range of damping conditions and respective deceleration of impacting particles. Single impacts were produced via wipe tests and bonding was evaluated by cavitation testing followed by SEM examination of impact and fracture morphologies. The results show that better bonding is achieved for material combinations with similar properties due to high adiabatic shear instabilities that result in microfusion at the particle-substrate interface. In the case of dissimilar materials, the conditions for bonding can be reached in an intermediate stage, but bonded areas may later separate due to particle movement around the interface.

In this work, Al and Al-Al 2 O 3 coatings up to 8 mm thick were cold sprayed on AZ91D magnesium alloy substrates. Microstructure, microhardness, bond strength, and corrosion and wear resistance were studied to assess the viability of using these coatings to restore dimensionally degraded parts and protect them from further corrosion and wear.

WC-Co cermet powders were deposited on aluminum substrates by cold gas spraying. XRD tests were run on the powder and coatings to reveal possible phase changes during spraying. Bonding strength, abrasive wear resistance, and corrosion resistance were also measured and are compared with values obtained from HVOF sprayed WC-Co coatings.

Inconel alloy coatings have been obtained by means of Cold Gas Spray technology with a high efficiency. Alumina has been sprayed simultaneously achieving an homogeneous distribution along the deposit with a good cohesion between particles. Furthermore, the alumina particles were found to improve the spraying feasibility. A proper optimization of the spraying conditions has been carried out in order to obtain the lowest porosity as possible and good embedment of the alumina. Then, the mechanical properties as well as tribological and oxidation behavior have been characterized. Alumina behaves as reinforcement leading to an amelioration of the abrasive and friction performance. Regarding the oxidation and corrosion behavior, the coatings proved to withstand reasonably well up to 800°C and salt fog tests (5% NaCl solution at 35 °C) indicate durability up to 1000 h.

Cold Gas Spray allows to extend the range of steel coating formulations in comparison with other thermal spraying techniques because the material doesn’t melt during process. The absence of processes of fast solidification implies the absence of tensile stresses in the coating and makes possible to obtain thick coatings becoming a new alternative to welding cladding processes for the restoration of surfaces with corrosion pitting, notched areas or welded zones with bad appearance and for the repair of porous casting, contractions or losses of tolerance, by applying located coatings. 17-4 PH steel is one of the most widely used precipitation hardening grades in the business, offering high strength with corrosion resistance similar to S30400 in most environments. While soft and ductile in the solution annealed condition, it is capable of high properties with a single precipitation or aging treatment. Characterized by good corrosion resistance, high hardness, toughness and strength. Commonly used in both aircraft and gas turbines, nuclear reactor, paper mill, oil field, and chemical process components. A study has carried out in Thermal Spray Center for the production and optimization of thick coatings of 17-4 PH steel (S17400) through Cold Gas Spray technology onto carbon steel substrates. The study concentrates in the determination of influence of spray parameters on coating properties.

Hydroxyapatite (HAp: Ca 10 (PO 4 ) 6 OH 2 ) is a biocompatible and bioactive ceramic material widely used as a coating on metal surfaces (dental implants, hip replacements ...), but the low adhesion between HAp and the substrate due to the differences in thermal expansion coefficients of both, and the degradation of HAp, is being improved through the addition of TiO 2 to reach a good combination of mechanical properties. Therefore, the objective of this project is to produce 80%HAp-20%TiO 2 (by weight) coatings on Ti6Al4V by High-Velocity Oxy Fuel (HVOF). The microstructure study has been carried out using scanning electron microscopy, and the characterization of the present phases, hydroxyapatite and rutile mainly, using X-ray diffraction and Raman spectroscopy (the last one to find out which are the minority phases, such as anatase and tricalcium phosphates). Also Rietveld method has been used to quantify the amount of amorphous phase, lower than in the case of plasma-sprayed coatings. The coatings adhesion has been measured by tensile tests according to ASTM C633-01(2008), finding an improvement over the adhesion of plasma sprayed coatings, and also of hydroxyapatite coatings; also their bioactivity has been evaluated through its immersion in simulated body fluid (SBF), and through in vitro tests to study osteoblast behaviour on the coatings surfaces, with positive results. To conclude, a discussion about the results is made to analyze the industrial viability of these kinds of coatings.

Corrosion is a very important problem in the Municipal Solid Waste Incinerator (MSWI) superheaters. This problem causes the plant stops and tube replacements, promoting the loss of energy generation rate. The main corrosion agent is the chlorine deposits. HVOF coatings have been sprayed to improve corrosion resistance of the superheaters inside the MSWI boilers. Inconel 625 and Hastelloy C22 alloys have been sprayed as a powder feedstock material. The spray process has been analyzed by a Spray Watch system that allows carrying out the temperature and velocity measurements of the particles in flight in order to optimize the spraying process. The produced coatings have been characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to evaluate the porosity and oxidation produced in the spray process. Laboratory oxidation test have revealed the formation of Cr 2 O 3 , NiO and Fe 2 O 3 as corrosion products as well as Microanalysis by Energy dispersion Spectroscopy (EDS) composition profiles have been used to evaluate the penetration of the corrosion front inside the coating. The Nickel alloys show a good resistance in aggressive environment test and can be a good solution for the corrosion problems in the superheater tubes in MSWI.

The Cr 3 C 2 -NiCr coatings were sprayed on an AA 7050-T7 alloy by HVOF Thermal Spray Process using AMPERIT 586.054 powder. The substrate was refrigerated during the sample preparation using liquid nitrogen in a device specially designed for this purpose. The spray conditions were also performed increasing the carrier gas flow or the oxygen flow. The XRD and SEM studies showed well-bounded coating/substrate interface, pores, metallic matrix, chromium oxides, carbides, and carbides dissolution into the matrix. The structure comparison between the samples showed a denser structure due to the increase in the carrier gas velocity and the highest carbide dissolution due to the high temperature achieved during the spray process. All samples showed similar wear abrasive behavior, and all of them showed wear rates 7 times higher than the aluminum alloy. All samples also showed corrosion resistance much higher than the AA7050 alloy in NaCl solution.

Producing nanostructured materials through metastable phases is an interesting novel route in the field of ceramic materials. Due to their small grain size and uniform structure, these nanostructured bulk materials exhibit very interesting properties. Metastable coatings can be produced starting from microstructured powders through atmospheric plasma spray (APS) technique, followed by a quenching route. The initial powders are melted during the spraying and deposited over a substrate that is quenched with liquid nitrogen (LIN) feeders, producing metastable coatings. The thermal sprayed coatings have been characterized using XRD, SEM, FESEM and EDS in the Thermal Spray Centre (CPT) of the University of Barcelona. The properties of such coatings have been also studied obtaining promising results.

This study examines the oxidation performance of two different iron aluminide coatings obtained by means of High Velocity Oxygen Fuel spraying starting from the same feedstock powder but using propylene and hydrogen as fuels. The isothermal oxidation tests were carried out at 900°C for 4, 36 and 72 hours. After detailed observation a more rapid oxide scale growth is obtained for that coating obtained under hydrogen conditions. It leads to the assertion that propylene-coatings would perform better under high temperature environments.

Recent research in the field of nanostructured ceramic materials has underscored the importance of using feedstock powders with metastable phases. During material consolidation the metastable structure evolves into a dual structure where the grain growth stops when the crystallites reach their respective equilibrium grain size. The mutual suppression of the grain growth is a direct consequence of the immiscibility of the two phases in the solid state. Due to their small grain size and uniform structure, the nanocomposites exhibiting very interesting properties, are formed. Metastable structures can be produced using atmospheric plasma spray (APS) technique. The main target of this work has been the synthesis of Al 2 O 3 -TiO 2 metastable powder through atmospheric plasma spraying (APS) and quenching route. The metastable phases have been produced from micron-sized feedstock powders and the effect of different raw powders have also been evaluated. The metastable phases have been characterised by XRD, SEM and FESEM analysis. The availability of producing nanostructured materials through these metastable phases have been studied. The phase and morphology evolution from this metastable phases to nanostructures has been observed.

The results for joints obtained by dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC-Co are shown in the present work. This high strength steel substrate was coated with WC-Co, sprayed by HVOF technique (Diamond Jet Hybrid DJH-2700) using propylene as fuel gas at different conditions. The dynamic diffusion bonding was carried out in a high frequency furnace, all joints were made in air. Before doing the joints, the steel was coated with Ni and Cu by electrochemical processes in order to obtain a soft 20 m interlayer of Ni30Cu alloy. Microstructure and reacted zones in the joints were investigated by means of Scanning Electron Microscopy (SEM) and Dispersive X Ray Spectrometry (EDX). In all joints different reacted zones can be distinguished, caused by diffusion processes which take place during the joint tests. The mechanical properties of the joints were quantified in a tensile machine, using a constant load of 0.1 MPa·s -1 . All joints broke by the WC-Co coating zone by delamination processes. The fracture surface was studied by SEM-EDX in order to know the fracture mechanism of the joints. The maximum tensile strength obtained confirm a very promising technology for industrial applications.

Over the last years, the grain size reduction to the nanometric scale has experienced an increasing interest because of its enhanced properties. This study is based on WC-Co cermet materials, which have a great application in the wear resistance materials field. In the Thermal Spray Center (CPT) of the University of Barcelona, two coatings using nanostructured and bimodal WC-Co cermet powders have been obtained by means of High Velocity Oxygen-Fuel (HVOF) technique. Both were sprayed under the same spraying parameters. Structural characterization for both feedstock materials and coatings have been performed using XRD, SEM and TEM. The friction wear resistance of the coatings has been studied by Ball-on-Disk test (ASTM G99-90), and the abrasive wear resistance has been quantified by Rubber-Wheel test (ASTM G65-91). Finally, the corrosion resistance has been studied by electrochemical techniques and a salt fog spray test. The nanostructured coating shows more hardness, but the bimodal coating shows better abrasive and friction wear resistance. Both coatings shows good corrosion resistance, better than the conventional coatings of WC-Co. The bimodal powder have the added advantage of being not as expensive as the nanostructured powder, and even providing better properties.