The effect of thermal history on microstructure of Er₂O₃ coating layer prepared by MOCVD process

Er₂O₃ is a high potential candidate material for tritium permeation barrier and electrical insulator coating for advanced breeding blanket systems with liquid metal or molten-salt types. Recently, Hishinuma et al. reported to form homogeneous Er₂O₃ coating layer on the inner surface of metal pipe using Metal Organic Chemical Vapor Deposition (MOCVD) process. In this study, the influence of thermal history on microstructure of Er₂O₃ coating layer on stainless steel 316 (SUS 316) substrate by MOCVD process was investigated using SEM, TEM and XRD. The ring and net shape selected-area electron diffraction (SAED) patterns of Er₂O₃ coating were obtained each SUS substrates, revealed that homogeneous Er₂O₃ coating had been formed on SUS substrate diffraction patterns. Close inspection of SEM images of the surface on the Er₂O₃ coating before and after thermal cycling up to 700°C in argon atmosphere, it is confirmed that the Er₂O₃ particles were refined by thermal history. The column-like Er₂O₃ grains were promoted to change to granular structure by thermal history. From the crosssectional plane of TEM observations, the formation of interlayer between Er₂O₃ coating and SUS substrate was also confirmed.