Abstract
Thermally sprayed ceramic coatings are applied for the protection of surfaces that are exposed mainly to wear, high temperatures, and corrosion. In recent years, great interest has been garnered by spray processes with submicrometric and nanometric feedstock materials, due to the refinement of the structure and improved coating properties. This paper compares the microstructure and tribological properties of alumina coatings sprayed using conventional atmospheric plasma spraying (APS), and various methods that use finely grained suspension feedstocks, namely, suspension plasma spraying (SPS) and suspension high-velocity oxy-fuel spraying (S-HVOF). Furthermore, the suspension plasma-sprayed Al2O3 coatings have been deposited with radial (SPS) and axial (A-SPS) feedstock injection. The results showed that all suspension-based coatings demonstrated much better wear resistance than the powder-sprayed ones. S-HVOF and axial suspension plasma spraying (A-SPS) allowed for the deposition of the most dense and homogeneous coatings. Dense-structured coatings with low porosity (4 vol.%) and good cohesion to the metallic substrate, containing a high content of α–Al2O3 phase (56 vol.%) and a very low wear rate (0.2 ± 0.04 mm3 × 10−6/(N∙m)), were produced with the S-HVOF method. The wear mechanism of ceramic coatings included the adhesive wear mode supported by the fatigue-induced material delamination. Moreover, the presence of wear debris and tribofilm was confirmed. Finally, the coefficient of friction for the coatings was in the range between 0.44 and 0.68, with the highest values being recorded for APS sprayed coatings.
Highlights
The development of highly advanced spray torches and a better understanding of coating deposition mechanisms have contributed to rapid progress in surface engineering [1]
This study aimed to investigate the morphology, microstructure, and wear resistance under dry friction conditions of Al2 O3 coatings deposited by different spray techniques, i.e., atmospheric plasma spraying (APS), suspension plasma spraying (SPS), axial suspension plasma spraying (A-SPS) and S-high-velocity oxy-fuel spraying (HVOF)
Both as-sprayed conventional APS and suspension-sprayed coatings exhibited a characteristic topography that is typical for thermally sprayed deposits (Figure 2)
Summary
The development of highly advanced spray torches and a better understanding of coating deposition mechanisms have contributed to rapid progress in surface engineering [1]. Requirements in many fields of machine operation and production techniques led to applications for various alumina-based coatings, for example, as electrically insulating or wear-protection layers [2]. Such coatings are primarily found in the machinery, marine, chemical, food, textile, printing, and energy industries [3,4,5]. The HVOF technique is characterized by high kinetic energy, relatively low temperature, and uses slightly smaller powders (i.e., −25 + 5 μm) than in APS [14] It enables the application of coatings with high density, favorable hardness, and increased adhesion [15]. It allows the improvement of the tribological properties, e.g., the abrasion wear resistance of the alumina-based HVOF coatings is reported to be two- to three-fold greater than the APS ones [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
