A Microstructural Comparison of NiCoCrAlY Superalloy Coatings Manufactured by Combustion Flame Spray and High-Velocity Oxygen Fuel Processes

NiCoCrAlY powders were thermally sprayed by combustion flame spray (CFS) and high-velocity oxygen fuel (HVOF) processes on IN 718 alloy substrates. Experimental parameters were fixed to manufacture coatings with a thickness about 200 μm. Microscopy and X-ray diffraction analyses were performed to reveal microstructural characteristics of both developed CFS and HVOF coatings, and it was observed that they were formed by a lamellar morphology composed of β and γ phases. The analyses also revealed lower porosity in the coatings produced by HVOF process while was compared with CFS process. While a microstructure composed of like-deformed powder was developed in HVOF process, in the case of CFS a building layer-by-layer was characteristic. Vickers hardness tests were also performed, and it was found that coating developed by HVOF process showed quite higher hardness values compared with those measured on the coatings developed with the CFS process, nonetheless this difference was small. Hence, the results showed that the coatings by CFS process are very promising for industrial applications, with negligible manufacture costs and very appropriate to be applied in situ.