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.

Sprayed deposits using conventional wire and powder materials open a wide range of possibilities to solve wear problems in engineering equipment. The option for new different spray technologies and consumables like nanostructured powder materials and nanocomposite cored wires has expanded the engineering possibilities. Cored wire technology allows the use of compositions that cannot be drawn into wire form like carbides in metallic matrix and high-temperature materials, thus intensifying the use of low operating cost welding and spraying processes to demanding wear applications. The objective of this work was to compare the mechanical characteristics and erosive wear performance of coatings obtained by Flame Spray and High Velocity Oxygen Fuel Spray using some selected powder and flexi-cord wire materials. The wear resistance of the coatings was determinate by slurry erosion wear test.

The main objective of this study is to compare the wear resistance of coatings obtained by gas metal arc (GMA) welding, wire arc spraying, and high-velocity oxyfuel (HVOF) spraying. Tungsten and chromium carbide (WC-Co and CrC-NiCr), iron alloy (Vecalloy B and 140-MXC), and 420 stainless steel coatings were deposited on low carbon steel substrates by the appropriate method. The coatings were examined by optical and scanning electron microscopy, showing no signs of spallation nor relevant level of defects. WC-Co coatings obtained by HVOF spraying exhibited the best abrasive wear resistance. Nanostructured Fe-alloy coatings applied by wire arc spraying performed almost 50% better than HVOF sprayed CrC and only 15% worse than WC-17Co. The erosion resistance of the two WC-Co coatings was very close, although WC-12Co was slightly better possibly due to its higher microhardness, lower porosity, and higher residual compressive stresses.

The superior mechanical properties of Boron Carbide make it very attractive for use as a wear resistant coating in tribological applications. Boron carbide is the hardest non-oxide ceramic produced in large quantities. It offers a high erosion and abrasion resistance, high chemical and outstanding heat resistance. B4C can be formed on a suitable substrate by thermal spray process as an alternative to high wear carbide coatings. The objective of this work was to investigate and to characterize the mechanical properties of a boron carbide based coating applied by HVOF spraying using a non commercial powder for corrosion and abrasion applications. The produced coatings were evaluated by metallographic procedure, microhardness, porosity and roughness measurements as well as adhesion and wear tests. The results are promising and signal good applications for such coatings.

The aim of this work is to assess the potential of HVOF-sprayed boron carbide-based coatings for protecting surfaces against abrasive wear. The results are evaluated by microstructure characterization, microhardness measurements, and adhesion and wear tests.

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.

The use of thermally sprayed coatings to improve wear and corrosion resistance of industrial components has been found to be an effective and viable choice. Coatings based on several materials can be used for such applications, including situations when they are combined, using distinct deposition methods. The analysis for choice of the ideal coating and application process should generally take into account both coating performance and cost. In this work a comparative study of three commercial coating materials is performed. The used coating materials are High Chromium (HCr), High Chromium + 420 Stainless Steel and 420 Stainless Steel + 1080 Carbon Steel wires applied by Electric Wire Arc Spaying. The obtained coatings are tested for wear (ASTM-G-65-91 rubber wheel test) and corrosion (ANSI/ASTM-B117 and Electrochemical Measurements). Coatings microstructure, microhardness and adhesion (ASTM-C633-85) are also evaluated.

The use of coatings to improve wear and corrosion resistance of mechanical components has been common for several decades. Various application techniques have been commonly used, including welding, cladding, electroplating, PVD (physical vapor deposition) and CVD (chemical vapor deposition). Thermal spraying has been found to be an interesting and viable alternative for those processes in such applications. Coatings of several types can be used for wear and corrosion protection, including situations when they are combined. The analysis for choice of the ideal coating and of the application process should take into account the environment and related limitations and specificities of each coating material and application process. In this work a study and characterization of tungsten and chrome carbides based coatings was carried out. The coatings were applied by high velocity oxy fuel thermal spraying (HVOF), using two different HVOF systems. Microstructure, hardness, as well as wear characteristics of the coatings were evaluated. The results show that the obtained coatings present great characteristics and can successfully face several wear conditions.

Cavitation is one of the most serious problems that affect hydraulic systems and components, mainly power turbines. Welding deposits have been traditionally used to protect components from cavitation damage. Since the protection process is normally associated to maintenance repairs (welding overlay), there are some difficulties related to weld distortion and residual stresses as well as some economic problems regarding to process efficiency and time. Thermal spraying has been recently tested as an alternative to welding in such applications. Some of the materials tested have been proved to be ineffective or inappropriate due to several causes like poor adhesion or mechanical damage. This work refers to a study of wear resistant coatings applied by thermal spraying and welding for cavitation resistance applications. The coatings were applied by High Velocity Oxygen Fuel (HVOF) and Flame Spraying and by Shielded Metal Arc Welding (SMAW). Hardness, roughness as well as cavitation resistance characteristics of the coatings were evaluated. The results show that the obtained coatings are promising for protection in cavitation resistance applications.

This paper presents the results of a study on WC-Co layers obtained by high-velocity oxyfuel spraying using different commercial systems. It explains how test samples were produced and how coating microstructure, hardness, and wear resistance was examined. The results show that the layers have excellent wear resistance and are suitable for many applications. Paper includes a German-language abstract.

Thermal barrier coatings have been extensively used in several industrial segments. The material used as an insulator in such systems has been partially stabilized zirconia (PSZ) plasma sprayed over a metallic bond coat layer. The ceramic layer is usually porous, thus improving insulation properties. The porosity also increases gas permeability and, therefore, reduces oxidation resistance of the coating. Post-treatments have been applied to reduce the open porosity and improve oxidation resistance. In this work thermal barrier coatings were applied on low carbon steel substrates using two sets of bond coat, i.e., metallic and metal-ceramic. The metallic bond coat was NiCrAlY. The metal-ceramic bond coat was a mixture of NiCrAlY and 8% yttria partially stabilized zirconia, which were applied by simultaneous feeding to the plasma torch from two powder feeders. A sol-gel method was employed to impregnate the porous ceramic top coat with alumina or zirconia. The samples in the as-sprayed and post-treated condition were characterized using mercury intrusion porosimetry (MIP), thermal conductivity. KEY WORDS: Thermal Conductivity, TBCs, Sol-Gel.

In this paper, the processes as well as the first results regarding the economic efficiency and plasma fuel properties of nanostructured zirconium oxide powder particles are explained. The paper evaluates values for porosity, hardness, roughness, and crystallite size. In addition, both the morphology of the powder particles and the spatter are analyzed by SEM, and cross sections of the coatings are observed using optical microscopy. These results are compared to coatings made from a commercially available yttria stabilized zirconia powder. Paper includes a German-language abstract.

In this paper, the mechanical properties and cracking features of yttria stabilized zirconia with and without bond coat on steel substrates is investigated. Four point bending tests have been used to evaluate the mechanical properties, while acoustic emission (AE) has been used to in situ monitor the cracking behavior during the bend tests. In the sprayed state, the samples were characterized by four-point bending tests with local noise emission. In comparison with the substrate, the coated samples showed an increased flow pressure. It is also shown that the processing parameters, the cooling, and the adhesive layer have a significant influence on the flow pressure. It is proven that the cooling affects the behavior of the load-displacement curves. The AE analysis shows the different deformation behavior of the coating-substrate system for the different processing conditions. This is supported by the surface crack analysis. Paper includes a German-language abstract.

Metal-ceramic coatings have been widely used for industrial applications, mainly in the thermal barrier coating technology (TBC). Plasma spraying is the common manufacturing process of TBC's. Conventional thermal barrier coatings consist of a metallic bond coat layer and an insulating ceramic overlay. Graded coatings or functionally gradient coatings have also been applied in order to solve the problems associated with the early spallation of plasma-sprayed conventional TBCs. Temperatures and gradients during plasma spraying have and important influence on the coating quality, specially the temperature of the particles just hitting the substrate surface. When applying so distinct materials like metals and ceramics this fact has an increased importance. In this work metal-ceramic coatings have been applied on metallic substrates. The interfacial temperature measurements were performed by optical pyrometry. The substrate temperature was measured by thermocouples. The adhesion of the coatings was determined by standard ASTM tests and correlated with the measured temperatures. In a general way, results show that the coatings with lower adhesion values were that with lower interfacial measured temperatures.