Influence of microstructure flaws on the tribological performance of Cr-based thermal-sprayed ceramic coatings

Abstract The technique of thermal sprayinghas been proposed since several years ago, as an alternative to Cr electrodeposition, a process characterized by the need of post-deposition handling of a large amount of toxic slurry wastes. Chromium oxide and chromium carbidecoatings, as well as Cr electrodeposits find applications, mainly, on the wear protection of metallic components participating in several tribosystems. In the present study, three different thermal sprayingtechniques were applied for the deposition of such ceramic coatings onto stainless steel substrates; namely, Flame Spraying (FS) and Atmospheric Plasma Spraying (APS) were employed for the deposition of chromium oxide coatings, whilst High Velocity Oxygen Fuel (HVOF) technique for the elaboration of chromium carbideones. Post-deposition evaluation of the coatings with respect to dry sliding against an Al 2 O 3 ball and a cBN-coated conical insert, as well as three-body abrasion performance according to the ASTM G65 technical specification, demonstrated that the APS oxide coatings exhibited superior tribological behavior during both tests, despite the fact that their microstructure was not free of flaws. Compared to APS ones, FS oxide coatings exhibited lower three-body abrasion resistance; however, their dry sliding wear resistance was of the same order of magnitude, being only marginally lower. This last characteristic advocates for the use of the much more flexible FS technique for the elaboration of chromium oxide coatings for applications where relatively low shear stresses are expected to be encountered. Finally, the HVOF carbide coatings showed intermediate three-body abrasion resistance but high sliding wear, the latter attributed to both microstructure flaws and in-flight decomposition of the feedstock carbide powder during deposition.