Nickel-aluminum alloys are widely used in harsh environments due to their corrosion resistance, high melting temperature, and thermal conductivity. In this work, Ni-5wt%Al coatings were deposited by twin-wire arc spraying (TWAS) on tool steel using a design of experiments approach to study the effect of process parameters on coating microstructure and performance. Test results presented in the form of process maps show how N2 pressure, stand-off distance, and current affect in-flight particle velocity and temperature as well as coating thickness and oxide content. Using this information, optimized coatings were then deposited on test substrates and subjected, along with uncoated tool steel, to several hours of molten aluminum attack. The coated samples showed no signs of physical or chemical damage, whereas the uncoated substrates experienced oxidation, aluminum infiltration, and formation of Fe-Al intermetallics.

Developing effective heating systems to prevent ice accretion on the surface of wind turbine blades and aircraft wings is of great significance for extreme cold environments. However, due to high velocity impingement of water droplets and solid particles on the surface of these components, an appreciable degree of surface material degradation may occur. In this study, nickel-chromium-aluminum-yttrium (NiCrAlY) was chosen as a metal matrix material for a coating-based heating system. Pure ceramic powders, namely, alumina and titania, and a cermet powder, tungsten carbide-cobalt (WC-12Co), were mechanically admixed with NiCrAlY powder and deposited to fabricate reinforced metal matrix composite (MMC) coatings. The powders were deposited on cylindrical low carbon steel bars by using flame spraying. The specimens were placed in a wind tunnel to conduct a comparative investigation of their erosive wear resistance under water droplet impact. A cold spraying unit was used for solid particle impact erosion tests. The erosive wear rates were quantified by measuring mass loss. The experimentally obtained results showed noticeably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania coatings compared to the other coatings. The results suggest that certain MMC coatings could be effectively employed to decrease the erosion rate of coating-based heating elements.

Hydroelectric turbines are strongly affected by cavitation and the damage it can cause to critical part surfaces and profiles. The study of thermal spray processes and materials is thus relevant to improving turbine performance. The main objective of this work is to evaluate the influence of fuel-oxygen ratio on tungsten- and chromium-carbide cermet coatings deposited by HVOF. Particle velocity and temperature were measured as were coating hardness, porosity, and cavitation resistance. Higher particle velocities were obtained at higher fuel ratios, producing harder, denser coatings with better cavitation resistance. Based on test results, the wear mechanism starts with the nucleation of the cavitation that occurs in the pores, resulting in the formation of craters and the eventual detachment of lamellae as indicated by the smoothness of the surface.

Two kinds of cermet powders, WC-10Co4Cr and WC-20CrC-7Ni, were deposited on 1040 steel via high velocity air fuel (HVAF) spraying to evaluate resistance in cavitation erosion conditions with additional electrochemical effects. Coating microstructure, phase composition, and microhardness were examined along with the topography of eroded surface layers. The cavitation resistance of the WC-20CrC-7Ni coating was found to be approximately 1.3 times greater than that of the other coating, which can be attributed to its finer grain structure, lower pore density, and the presence of high Cr and Ni content in the feedstock powder which serves to strengthen the matrix.

High-velocity oxyfuel (HVOF) sprayed coatings of Cr3C2-NiCr containing solid lubricants such as nickel cladded graphite and hexagonal boron nitride were successfully developed and characterised with the aim of optimizing their friction and wear behaviour. HVOF technology was used for the integration of solid lubricants to achieve strong cohesion between particles while minimizing thermal decomposition. Coating microstructure and composition were measured and correlated to the results of tribological and corrosion tests. The integration of the solid lubricant greatly reduced friction and wear volume at room temperature, but the lubricating effect was highly dependent on atmosphere and temperature. Cr3C2-NiCr with hBN, however, tends to exhibit more stable wear resistance over a wider temperature range and can be used at temperatures beyond 450 °C.

The effect of deposition pressure on the microstructure and ablation behavior of ZrB2 coatings deposited by very low pressure plasma spraying is investigated. The results show that under a chamber pressure less than 50 kPa, as the spray chamber pressure decreases, the porosity of the coating deposited at the same distance decreases, and the coating prepared under 100 Pa presents the lowest porosity of 1.79 %. Furthermore, among the ZrB2 coatings deposited at 100 Pa, 5 kPa, 10 kPa and 50 kPa, the dense coating deposited at 100 Pa showed the lowest ablation rate of 0.33 μm/s, 0.75±0.08 mg/s.

Metal structures in offshore facilities are usually protected from corrosion using Zn-Al coatings even though they are subjected to collective stress conditions. This paper evaluates a post-treatment called machine hammer peening and its effect on surface finish, induced residual stresses, and near-surface microstructure of thermally sprayed ZnAl4 coatings. As expected, coating roughness was reduced from about Rz = 53.5 μm in the as-sprayed condition to 10.4 μm after treatment and coating densification was revealed in the near-surface zone. Residual stresses, which were surprisingly compressive in the as-sprayed condition, were likewise affected by the peening process, reaching a maximum of 200 MPa. The influence of peening direction and other such parameters were also investigated as part of the study.