Residual Stress Measurement And Numerical Simulation Of Al₂O₃ Tritium Penetration Barrier On The Surface Of 316L Stainless Steel

Al₂O₃ coating is normally prepared on the surface of 316L stainless steel as a very good tritium penetration barrier, to improve the penetration resistance of the substrate.However, direct preparation of the coating on the substrate easily results in cracks or debonding at the interface between Al₂O₃ coating and the substrate of 316L because of the mismatch of their thermal expansion coefficients.Moreover, dense Al₂O₃ and porous Al₂O₃ with different proportion of porosities have great effect on the residual stresses in the coating and at the interface. The distribution of residual stresses after the fabrication of Al₂O₃ coating is simulated by using nonliner MARC software in this work to obtain the regularity of residual stresses distribution in the different coatings, and optimise the coating structure with good thermal shook resistance.The porosity in porous Al₂O₃ coating has no effect on the distribution of residual stress in the coating, but affects the value of the stresses greatly. The maximum value of residual stresses decreases with the increase of the porosity. The calculated thermal stresses in dense Al₂O₃ coating were much larger than those in porous Al₂O₃ coating when the thickness of both dense and porous Al₂O₃ coating was the same. The maximum value of residual stresses of Al₂O₃ coating is in proportion to the coating thickness.Meanwhile, when the magnitude of the coating thickness increases, the location of the maximum stress concentration is shift from the coating to the substrate. The distribution of Al has a great effect on the distribution of Al₂O₃ gradient coating because Al₂O₃ coating was obtained though the oxidation of the aluminized coating, therefore the gradient Al coating should be analyzed. It was found that the residual stresses in the coating were decreased with increasing the magnitude of p, the coatings thickness, and the number of graded layers. The Al₂O₃ functionally gradient coating (FGM) was designed to avoid stress concentration between the coating and the substrate of 316L.Compared with non-gradient material (NFGM), thermal thermal stresses in optimized FGM were remarkably alleviated. The best parameters of FGM Al₂O₃ coating were the compositional exponent (p) of 1.0 and the number of the coatings (n) of 9.Further more, Al₂O₃ gradient coating was fabricated on the surface of 316L stainless steel with the aid of plams spraying and was characterized with XRD, SEM and other instruments. The average residual stresses at the different positions of Al₂O₃ coating were measured by X-ray diffraction approach to verify the reliability of the simulation. Finally, both the experimental results and the calculation results were compared and analysed.