Iron-based coatings are often considered as replacement of hard chromium and WC-Co, as they pose lower health and environmental impact. In many cases the combination of mechanical and chemical properties of ferrous based alloys may be satisfactory and their relatively low cost make these coatings an interesting candidate for many applications. This study is inspired by opportunities to harden the ferrous base materials by strain hardening, solid solution strengthening, dispersion strengthening, and precipitation hardening. Already commercially available Fe-based coating materials with precipitates of mixed carbides and borides in the metastable austenitic matrix achieve a high hardness. In this study the cavitation erosion and abrasion resistance of various Fe-based coatings produced by HVAF and HVOF processes were investigated. Two experimental precipitation containing materials were prepared, and the sprayed coatings were tested for abrasive and cavitation erosion wear. In addition to precipitations, the importance of proportion of ferrite and retained austenite phases were studied by affecting the microstructure by heat treatments as the ability of different phases to affect hardening and ductility may become crucial in generating desired material properties. The properties of experimental and some commercial Fe-based alloys are compared with WC-Co and Cr 3 C 2 -NiCr coatings by property mapping.

Tungsten carbide -based hard metal coatings are extensively used in demanding industrial applications like for wear protection purposes. Continuously increasing demands set new limits and need for materials with enhanced features. One solution is to improve hard metal properties by nanostructures. Presented study is part of a research where novel and safe route to manufacture nanostructural WC-Co powders starting from water soluble raw materials was developed. In this study powders’ workability in thermal sprayings is studied. WC-12Co powder was manufactured using water soluble raw materials: ammonium metatungstate as a tungsten source, glycine as a carbon source and cobalt acetate as a cobalt source. The powder was manufactured via optimized spray drying and heat treatment method producing a correct phase structure and chemical composition. Experimental powder was sprayed by HVAF-spraying to study its workability and functionality. Morphology, microstructure and properties were analyzed from the experimental nanostructural powder and the HVAF-coatings.

This study assesses the sliding wear and impact behavior of thick carbide coatings deposited on hot-rolled steel by high-velocity airfuel (HVAF) spraying. Coating samples are evaluated based on scratch, ball-on-disc sliding, normal impact, and compound sliding impact tests and efforts are made to rank materials according to tribological criteria including coating failure mode, friction response, and wear. The approach is intended to provide insights for product designers specifying thermal spray coatings for steel components and structures from a wear performance perspective.

This work assesses the effects of defects in thermally sprayed chromia via multiscale modeling and imaging techniques. Defect distributions in coating samples are identified by way of image processing and synthetic 3D microstructures are generated from extracted statistical information. The properties of the microstructures are determined by subjecting them to simulated tensile testing, and the significance of different types of defects is evaluated through defect-containing coating models. The approach is able to handle complex defect morphologies, including pore, crack, and splat boundary clusters, making it a versatile tool for assessing the influence of defects on component performance.

In this work, a CFD model is built to investigate gas flow and in-flight particle characteristics in HVOF spraying with hydrogen as the fuel. Gas flow is solved for a particle-free jet, combustion is represented using a simple eddy-dissipation model, and a time-averaged fluid flow (k-ε) model is used to account for turbulence. Acceleration and heating of individual particles are modeled in a "snapshot" of the gas flow. Particle acceleration is shown to be governed by drag and particle heating by conduction and radiation between particulates and gas phases. Modeling results agree well with experimentally obtained data and observations.

Alloys with high amount of chromium are used for protection of power plant boilers against high temperature corrosion, especially heat exchanger surfaces, such as superheaters. Thermal spray coatings can be applied to low alloyed steel in order to enhance the lifetime of the cheap substrate material. In this study NiCr (50Ni49Cr1Fe) powder was sprayed with DJ Hybrid and CJS HVOF techniques, and the spraying process was optimized with process map methodology, including SprayWatch for measuring the temperature and velocity of the spray stream, and ICP (In-situ coating property measurement) for measuring the stress state. Different spraying parameters were applied in order to attain the best suitable coating characteristics for high temperature applications, such as high density and low oxidation stage. The coatings were analyzed e.g. by microscopic means and mechanical testing. The use of process optimization, process-structure- properties methodology, and following coating characteristics are presented.

HVOF-sprayed WC–10wt%Co–4wt.%Cr coatings were obtained using experimental feedstock powders (manufactured by spray-drying + sintering), containing nanometric carbide particles. Three reference coatings were also deposited using commercially-available powders containing sub-micrometric carbide particles. The coatings obtained from nanostructured powders, although affected by decarburisation phenomena, contained very fine carbide particles (~200 nm size). Those obtained from commercially-available powders simultaneously exhibited sub-micrometric (~400 nm size) and micrometric carbide particles, and were much less decarburised. Sliding wear tests performed at room temperature against sintered Al 2 O 3 balls showed the occurrence of brittle fracture wear (detachment of near-surface material by local brittle cracking) on the nanostructured coatings, which were embrittled by decarburisation. The reference coatings, by contrast, exhibited either ductile wear behaviour (plastic deformation, pull-out of single carbide particles) or a mix of both ductile and brittle wear mechanisms. When the decarburisation of the nanostructured coatings was not too extensive, their wear loss was comparable to that of the reference ones. At 500 °C, the wear behaviour of all coatings was dominated by abrasive grooving, on account of thermal softening. The most decarburised nanostructured coatings, however, still experienced brittle cracking as well.

Superior wear performance combined with excellent friction properties against metals makes chromium oxide (Cr 2 O 3 ) an interesting coating material for many industrial applications. However, Cr 2 O 3 is a challenging material for HVOF spraying due to its high melting temperature. Fracture toughness and lamella cohesion of a coating is limited and may be improved by using ceramic-ceramic –nanocomposite powders, which forms phases with improved properties. In this study Cr 2 O 3 -TiO 2 systems were selected aiming to improve the toughness and lamella cohesion of coating without reducing the excellent wear properties.