Effects of thermal spray processes on the development microstructure and thermal properties of NiCrAlY bond coats deposited over superni C-263 aero engine combustor liner alloy

Abstract Thermal barrier coatings need extremely durable and suitable bond coats to survive in high temperature environments. Ceramic top coat spallation is a significant problem in TBCs, which occurs mainly due to high temperature corrosion, thermally grown oxide stresses and erosive wear. The bond coat offers oxidation protection and ensures strong adhesion between the base material and the ceramic coating. The performance of the NiCrAlY bond coats ishighly dependent on the deposition process that controls their microstructure, porosity, thermal behavior and to thermal cycling resistance. Hence, this study aimed to investigate the microstructure, thermal expansion behavior and thermal conductivity of NiCrAlY bond coats applied over C-263 aero engine combustor liner alloy using atmospheric plasma spraying and high velocity oxy fuel spray techniques. The results indicate that high velocity oxyfuel spray coatings exhibit dense microstructure, reduced porosity and improved thermal properties compared to those developed by atmospheric plasma spray process. Further, an attempt has been made to evaluate thermal conductivity of the developed NiCrAlY bond coats using Guarded Hot Plate apparatus designed as per ASTM standard, E-1530-11. High velocity oxyfuel sprayed coatings show linearly increasing coefficient of thermal expansion (CTE) values (12−20 × 10−6 m K−1) and thermal conductivity, similar to the C263 substrate material. The XRD results in this investigation confirmed that the NiAl3 phase was absent in both APS and HVOF coatings, showing phase stability and compatibility. The reduced thermal conductivity was observed in the plasma sprayed bond coats. This study provides more insights in the development NiCrAlY bond coats for TBC applications.