In this study, alumina coatings were formed using atmospheric plasma spraying, increasing the torch power from 29.4 to 45.1 kW. The surface morphology of the coatings was determined using scanning electron microscopy; the elemental composition was examined using energy-dispersive X-ray spectroscopy (EDS); phase composition was investigated using X-ray diffraction; and surface roughness was determined using a profilometer. The steel surface temperature was measured using a type-K thermocouple, and the plasma jet temperature, at a distance of 70 mm, using a type-B thermocouple. Alumina particle velocity was calculated by analyzing high-speed camera footage using ImageJ software. The results indicate that plasma jet temperature, speed, and in-flight particle velocity increased with plasma torch power. Furthermore, the amount of γ-Al₂O₃ phase in the coating increased, and the α-Al₂O₃ decreased with increasing plasma power. The surface roughness (R_q) of the Al₂O₃ coatings decreased from 7.13 to 5.54 μm, with an increase in torch power. The EDS measurements indicate that the increase in torch power did not affect the elemental composition of as-sprayed coatings. The results provide a wider understanding of an atmospheric plasma spray technique, optimizing and controlling the parameters using air as a primary gas.

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. Coatings of compositions of Al₂O₃, Al₂O₃-3 wt.% TiO₂, Al₂O₃-13 wt.% TiO₂, and Al₂O₃-40 wt.% TiO₂ were deposited on steel substrates with a Ni/Cr bond layer by plasma spraying. The coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate their morphology, elemental composition, and crystalline phases. Electrochemical tests were performed in a naturally aerated 0.5 mol/L NaCl solution and cyclic thermal–chemical exposure tests (500 °C using 35% KCl) to assess their corrosion kinetics and thermal stability. The results indicate that pure Al₂O₃ and low TiO₂ (3 wt.%) coatings exhibit fine barrier properties, while coatings with a higher TiO₂ content develop additional phases (e.g., Ti₃O₅, Al₂TiO₅) that improve thermal resistance but reduce chemical durability.

This study presents the thermal and chemical resistance of plasma-sprayed Al₂O₃ and Al₂O₃ doped with 13 wt.% of TiO₂ coatings and their suitability for the fire grate of straw pellet furnaces. Coatings were deposited on steel substrates using direct current atmospheric pressure plasma spraying. The surface structure, elemental, and phase composition of formed coatings were analyzed before and after the thermal treatment, imitating natural application conditions. For the experiment, the annealing temperature was 500 °C for twenty-five cycles (80 min each). It was found that the steel substrate oxidized after five thermal cycles, and the formation of iron oxides was observed. The elemental composition of the Al₂O₃ and Al₂O₃-13 wt.% TiO₂ coatings remained unchanged even after 25 cycles of heat treatment. The X-ray diffraction (XRD) results revealed that the alpha-Al₂O₃ to gamma-Al₂O₃ phase ratio in the Al₂O₃-TiO₂ coating was reduced by only 8.7% after 25 cycles.

In this article, the results of thermal and chemical resistance, of plasma sprayed Al₂O₃ and Al₂O₃-13wt.TiO₂ coatings on a steel (P265GH) sample are presented. Coatings were formed using air-hydrogen plasma direct current plasma torch at atmospheric pressure. The resistance of coatings was measured by analyzing surface structure, elemental and phase composition of as sprayed coatings and after several heating cycles, imitating application conditions. To make this technology more appealing, by decreasing exploitation cost of standard cast iron grate used in straw pellet broilers, we used cheaper stainless steel with a protective Al₂O₃ and Al₂O₃-13wt.% TiO₂ coatings. Most of the research done in this field is by using Ar as primary gas, but to decrease the manufacturing cost even further we used Air as primary gas. It was determined that after heat treatment the minor changes in the elemental composition were observed. Meanwhile an additional crystalline phases of metal oxides were detected.