Investigating the transition time reduction in evaporation of NiCrAlY using EB–PVD

Abstract

Thermal barrier coatings have been widely considered owing to increasing efficiency of gas turbine engines. These coatings are often available in ceramic, thermally grown oxide and metallic bond layers. The function of metallic bond layer in these coatings is adhesion improvement and substrate protection. This layer can also be applied for electron beam–physical vapour deposition (EB–PVD). Yet, EB–PVD method cannot control evaporation process to be able to induce a deposit with uniform chemical composition along the coating thickness. The present study investigates composition variation during evaporation process of Ni–20Cr–11Al–0·3Y alloy using computational models and experimental results along with transition time prediction by computational model. To this end, EB–PVD by an electron gun with power of 3 kW in 4–6×10⁻⁵ mbar vacuums was used. The results indicated that applying an initial molten pool with a composition similar to that of equilibrium pool (Ni–2Cr–15Al–0·5Y) decreases transition time by 70%.