In this study, 316 stainless was deposited by low-pressure plasma spraying under various conditions to obtain different coating structures and by cold gas dynamic spraying for comparison. The coatings were characterized by cross-sectional metallography to assess porosity, oxidation, particle flattening, and elemental composition. The samples were also subjected to flyer plate impact testing in a gas gun to determine their shock propagation and porosity compaction properties. Comparing the results with that of the reference sample shows the effect of deposition conditions on the dynamic behavior of the coatings.

Amorphous coatings, despite their high strength and hardness and outstanding corrosion and wear properties, have been limited in application due to poor bonding strength and low impact resistance. This paper reviews the progress that has been made in that regard through the addition of ductile metals, ceramic particles, and polymer phases and through laminar structure design consisting of alternating amorphous and NiCrAl layers. Test results show that the composite amorphous coatings realized by the various methods exhibit significantly improved bonding strength and impact resistance along with their other superior properties.

As compared to thermal spray techniques, cold spraying allows to retain metastable phases of the feedstock material like amorphous structures, due to lower process gas temperatures. Compared to crystalline metals, metallic glasses are brittle at ambient temperature but viscous at higher temperatures. Therefore, cold spray parameters must be optimized for conditions that allow softening of the amorphous spray material for successfully producing coatings. For this study, a FeCoCrMoBC metallic glass was used that in comparison to others offers advantages with respect to higher hardness, less costly feedstock powder and minimum reactivity with the environment. Necessary impact conditions were investigated to meet the window of deposition. According to calculations and cold spray experiments, neither the glass transition temperature Tg nor the melting temperature Tm can describe required conditions for bonding. Thus, a so called softening temperature between the glass temperature and the melting temperature had to be defined to calculate the critical velocity of metallic glasses. With respect to the bonding mechanism, impact morphologies could prove that a transition to viscous flow gets more prominent for harsher spray conditions. By sufficiently exceeding critical condition for bonding, coatings with rather dense microstructures can be processed at deposition efficiencies of about 70 %. The coatings have a hardness of 1100 HV 0.3, but the results also demonstrate that further work is still needed to explore the full potential for bulk metallic glasses.

Thermal-sprayed (i.e. LPPS or HVOF) MCrAlY coatings are widely used for land-based gas turbine applications against high-temperature oxidation and hot corrosion. However, due to requirement for further improvement of turbine efficiency, dense and stable coatings are necessary. The cold spray (also referred to as cold gas dynamic spray) makes it possible to increase coating density, due to high velocity particle impact during spraying. However, deposition mechanisms of cold spraying have not been elucidated yet. In this study, we investigated the deposition mechanisms focused on the behavior of interface between a coating and a substrate. The mechanisms were evaluated by the spray impact phenomena simulation tests, namely laser shock flier impact tests, and STEM-EDX elemental analyses at the interface between the substrate and the cold sprayed coating. From the results of STEM-EDX for as-sprayed coating and of SEM-EDX of the flier specimen, the bonding between the CoNiCrAlY coating and the substrate occurred at the only particular phase combination.

In the kinetic spraying process, the critical velocity is an important criterion which determines the deposition of a feedstock particle onto the substrate. It was experimentally and numerically proven that the critical velocity is determined by the physical properties and the state of materials such as initial temperature, size and the extent of oxidation. Compared to un-oxidized feedstock, oxidized feedstock required a greater kinetic energy of the in-flight particle to break away the oxide film during impact. The oxide film formed on the surface of particle and substrate is of a relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide significantly affected the deposition behavior and critical velocity. The effects of oxidation on the critical velocity and the deposition behavior of the feedstock were investigated and evaluated by individual particle impact tests in this study. The velocity of pure Al particles was measured for a wide range of process gas conditions.

In some applications like car armouring for personal safety, in bulk containers in pebbles working, in off-shore applications or in offroad-vehicles, impact of bodies with different sizes and high velocities has to be calculated in material design. A possibility to design under economical aspects is to use to low-cost material as substrate with a protective coating on its surface instead of using expensive bulk materials. One conceivable material system to be used as protective coating is WC-CoCr, which is usually applied by HVOF and shows high hardness combined with a good toughness of the matrix. These properties are very important for dissipation of the impact energy and for high fracture toughness. In the presented case study, WC-CoCr coatings with different carbide sizes were produced with the JP5000 system from TAFA. Projectiles with high velocities of more than 250 m/s were shot by an experimental shooting device on the coatings and for comparability on the uncoated substrate. Impact tests were done with balls and cylinders with varying impact angles between 10° and 90°. The powders and the coatings were characterized by means of microscopy and XRD. Furthermore, the hardness of the coatings was measured. After impact tests, the coatings were investigated with optical microscopy. In the case of ball impact, a significant dependency can be found between the impact behaviour and carbide size. Coatings with coarse carbides show the lowest impact depth. The dependency of the impact depth of coatings with one carbide size on their hardness level is relatively low. No dependencies of the carbide size or the hardness level can be found for impact with cylinders.

The aim of this study was to investigate potential weight savings using multi-layer blade containment systems for turboengines. The association of an external ductile layer with an internal hard layer could provide a good ductility of the armor with the capability to withstand the perforation of high kinetic projectiles. Comparisons between several thick deposits obtained by the vacuum plasma spray process were performed using a Charpy impact testing machine. Mechanical and structural characterisations of these two-layer structures were performed and compared to the behavior of monolithic ones. Heat treatment effects were also considered.

Spray and Fuse coatings are ideally suited to boiler environments. The fusing step gives to optimized coatings a uniform chemistry and microstructure, a metallurgical bonding, no through porosity, a low oxide content and no cracking. The relative simplicity of the traditional processing equipment is suited to on-site and automated application including coating repair. Although enjoying considerable success in traditional boilers, their advance into new applications appears restrained by the issue of substrate property modifications during fusing. This paper studies the modification in substrate boiler tube materials (microstructure and mechanical properties) associated with the coating of advanced NiCrBSi alloys. Charpy impact, tensile strength, yield strength, elongation and thermal expansion coefficient testing between 22°C and 450°C are measured. By optimal coating design to a specific substrate, the effect on mechanical property modifications by fusing could be dramatically reduced to allow new and reliable coatings systems to be demonstrated for advanced applications. The future for Spray and Fuse coatings in boilers is discussed.