Characterization and Early-Stage Oxidation Behavior of CoNiCrAlY/Nano-Al2O3 Composite Coatings Using Satellited Powders Deposited by HVOF and LPPS Processes

In this study, satellited CoNiCrAlY/nano-Al2O3 feedstocks with 2 wt.% of oxide nanoparticles and pure CoNiCrAlY powder were deposited by the HVOF and LPPS processes on Inconel738 superalloy substrates. Microstructure and phase composition of powders and coatings were characterized by FESEM and XRD, respectively. The early-stage oxidation test was done at 1050 degrees C for 10 min. The results showed that the satelliting seems to be a promising method to produce nano-particles dispersed composite powders suitable for thermal spraying. Adding alpha-Al2O3 nanoparticles increased the porosity of the HVOF and LPPS coatings from 0.6 to 1 and from 2 to 2.45 vol.%, respectively. In the HVOF-sprayed CoN-iCrAlY/nano-Al2O3, coating including gamma-Co,Ni,Cr, b(Co,Ni)Al, and alpha-Al2O3, the growth of non-protective NiO and spinel oxides was significantly limited and a dense aAl(2)O(3) oxide layer was promoted after the early-stage of oxidation. However, for the LPPS-deposited CoNiCrAlY/nano-Al2O3 coating consisting of gamma-Co,Ni,Cr and c-Al2O3, after oxidation, the presence of Al-rich oxides like h-Al2O3 whiskers and porous transformed a-Al2O3 were observed on the coating. The correlation between microstructure, phase composition, and early-stage oxidation was discussed in detail.