Characterization and hot corrosion performance of LVPS and HVOF-CoNiCrAlYSi coatings

• Published in: Vacuum 2012-04, Vol.86 (10), p.1458-1464
• Main Authors: Mohammadi, M., Javadpour, S., Jahromi, S.A.J., Shirvani, K., Kobayashi, A.
• Format: Article
• Language: English
• Subjects: Coatings; CoNiCrAlYSi coating; Flame spraying; Fluxing mechanism; Hot corrosion; HVOF; LVPS; Nucleation; Oxide morphology; Oxides; Oxy-fuel; Sprayers; Sprays
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/j.vacuum.2012.02.030

The CoNiCrAlYSi coatings were produced by using low vacuum plasma spray (LVPS) and high velocity oxy-fuel (HVOF) techniques on the Inconel-738. Hot corrosion behavior and microstructure characterization was investigated by exposing the sample to a molten film of Na2SO4-20٪ wt NaVO3 at 880 °C for up to 560 h. The hot corrosion rate was determined by measuring the weight gain of the specimens at regular intervals for a duration of 20 h. The result of weight change measurements showed better hot corrosion resistance for HVOF-CoNiCrAlYSi coatings. This was attributed to the α-Al2O3 nucleation during the HVOF coating process and replacement of non-protective oxide due to a fluxing mechanism. It was also observed that the non-protective and porous oxides such as (Co,Ni)Al2O4 and (Co,Ni)Cr2O4 were formed on the both types of coatings due to large β-depleted zone after long exposure time of hot corrosion testing. ► Development of CoNiCrAlY coating by using low vacuum plasma spray and high velocity oxy-fuel. ► Hot corrosion behavior and microstructure change of coatings at 880 °C in the Na2SO4-20%NaVO3 salt. ► More lifetime of HVOF coating due to formation of dispersed α-Al2O3 in the HVOF process. ► Change of oxide morphology due to spallation and acidic fluxing are the main degradation mechanisms of these coatings.