Simulation of thermal stress in Er₂O₃ and Al₂O₃ tritium penetration barriers by finite-element analysis

The physical vapor deposition method is an effective way to deposit AI₂O₃ and Er₂O₃ on 316L stainless steel substrates acting as tritium permeation barriers in a fusion reactor. The distribution of residual thermal stress is calculated both in Al₂O₃ and Er₂O₃ coating systems with planar and rough substrates using finite element analysis. The parameters influencing the thermal stress in the sputter process are analyzed, such as coating and substrate properties, temperature and Young’s modulus. This work shows that the thermal stress in AI₂O₃ and Er₂O₃ coating systems exhibit a linear relationship with substrate thickness, temperature and Young’s modulus. However, this relationship is inversed with coating thickness. In addition, the rough substrate surface can increase the thermal stress in the process of coating deposition. The adhesive strength between the coating and the substrate is evaluated by the shear stress. Due to the higher compressive shear stress, the AI₂O₃ coating has a better adhesive strength with a 316L stainless steel substrate than the Er₂O₃ coating. Furthermore, the analysis shows that it is a useful way to improve adhesive strength with increasing interface roughness.