Compounds of the material group known as MAX phases combine metallic and ceramic properties. In this work, MAX-phase coatings are deposited from modified Ti 3 SiC 2 and Ti 2 AlC commercial feedstock powders using HVOF and atmospheric plasma spraying (APS). Feedstock powders and coatings were studied by microscopy and XRD. Despite the use of unoptimized powders, well adhering and relatively dense coatings were produced. HVOF-sprayed layers had denser microstructures with higher amounts of MAX phases. Optimizing the shape and particle-size distribution of feedstock materials is expected to improve coating properties.

This paper presents the results of corrosion investigations performed on thermal spray coatings with different compositions in the Al 2 O 3 -TiO 2 system. The coatings were deposited on stainless steel via APS and HVOF spraying and metallographically prepared cross sections and surfaces were characterized before and after corrosion testing in NaOH and H 2 SO 4 solutions at various temperatures. Opposite of expectations, APS coatings were found to be more corrosion resistant than the denser HVOF-sprayed layers.

Corrosion protection has long been a challenge to thermally sprayed coatings. Alumina is known for its good corrosion properties, although especially thermally sprayed alumina-based coatings corrode if exposed to certain environments. The coating therefore becomes the limiting part for the component lifetime. Besides the corrosion of the coatings themselves, corrosion of the substrate can result from the existing porosity in the coatings. This work shows the influence of corrosion on alumina-based coatings as a function of the TiO 2 content and the coating process used. The effects of corrosion are quantified to enable lifetime prediction and tailoring of protective coatings. The coatings were analyzed using electrochemical methods and were exposed for long periods to acids and bases at 85 °C. Corrosion properties of the coatings were compared with those of bulk parts, prepared by hot-pressing. An electrochemical method was developed to estimate interconnected of porosity as an alternative to long-term corrosion experiments.

Oxide-bonded silicon nitride (OBSN) powders have been developed to address thermal spray problems associated with high temperatures. This paper examines how such powders perform when applied via detonation gun (DGS) and atmospheric plasma spraying (APS) with axial powder injection. All coatings were characterized using optical microscopy and X-ray diffraction with additional tests being performed on DGS coatings. For the first time, relatively dense Si3N4-rich coatings with an oxide binder phase were produced, and some of the DGS coatings were found to be sufficiently wear resistance for industrial use.

Thermal spraying of silicon nitride has been considered impossible because the high temperatures involved lead inevitably to decomposition/oxidation of the material. To address these issues, improved silicon nitride-based powders were developed, two of which have been tested as reported in this paper. The powders were applied using low pressure plasma spraying (LPPS) and the resulting coatings characterized based on microhardness, adhesion, and cohesion strength. Phase transformations of the powders during spraying were also investigated and preliminary optimization strategies by statistical variation of plasma spray parameters were tested.