Thermal barrier coating on Inconel 718: understanding cyclic oxidation kinetics

Abstract

This study investigates the cyclic oxidation behaviour of a thermal barrier coating (TBC) system applied to Inconel 718 alloy substrates. The TBC comprises a NiCr bond coat and a YSZ top coat, applied using the air plasma spray method. Cyclic oxidation studies involve subjecting the coated samples to repeated heating and cooling cycles, with mass gain measurements taken after each cycle. Vibrational modes and surface morphology are analysed before and after oxidation. Results reveal a gradual increase in mass gain up to the 4th cycle, attributed to interface bonding and diffusion-limited growth. Thermal cycling induces stresses, leading to micro cracking and accelerated oxidation. Oxidation kinetics follows both parabolic and linear laws, with rates decreasing over cycles. Kl values consistently exceed Kp, indicating faster linear growth. The study enhances understanding of TBC behaviour under cyclic oxidation conditions, critical for improving durability in practical applications.