The purpose of this study is to determine if a GTAW (TIG) repair weld under an APS ceramic coating would cause a reduction in adhesion strength. Two stainless steels and a titanium alloy were selected for the study. For each material, 300 buttons were machined and further processed in groups of 50 through the application of one-pass, three-pass, or full pad welds. Welded buttons were lapped parallel to within 0.0002 in. and their lengths were compared with measurements obtained from buttons that had not been welded. NiCrMo bond coats were applied by HVOF spraying to both welded and unwelded samples, which were then top-coated with a ceramic layer (Cr 2 O 3 , Cr 2 O 3 -Al 2 O 3 , or TiO 2 ) deposited by air plasma spraying. A ten-cycle heat treatment was conducted on half of the samples to determine if the weld would amplify thermal expansion stresses. Based on adhesion test results, the welding had no measurable effect on adhesion strength nor did the heat treatment. Heat input from the HVOF flame and the plasma jet was sufficient to reduce weld-related solidification stresses.

Base metal surfaces are typically prepared for thermal spraying by chemically cleaning followed by grit blasting. In common practice, HVOF coatings are applied within 2-4 h or the entire cleaning process is repeated to prevent in-service adhesion failures. This study was initiated to assess the effect of long wait times on the adhesion strength of WC-Ni coatings. Test coupons were chemically cleaned, grit blasted, and then set out in shop conditions for up to 48 hrs. Some were also subjected to different forms of contamination including dirty fingerprints, grease, penetrating oil, surface rust, tape residue, and paint. Pull test and metallographic examination results show that none of the contaminants had an influence on the adhesion strength of the HVOF coatings.

Atmospheric plasma spraying has emerged as a cost-effective alternative to traditional sintering processes for solid oxide fuel cell (SOFC) manufacturing. However, the use of plasma spraying for SOFCs presents unique challenges, mainly due to the high porosity required for the electrodes and fully dense coatings required for the electrolytes. By using optimized spray conditions combined with appropriate feedstocks, SOFC electrolytes and electrodes with required composition and microstructure could be deposited with an axial plasma spray system. In this paper, the challenges for manufacturing SOFC anodes, electrolytes, and cathodes are addressed. The effects of plasma parameters and different feedstocks on coating microstructure are discussed, and examples of optimized coating microstructures are given.