Design, fabrication, and hydrogen blocking performance of alumina/zirconia functional gradient coatings

Abstract

When electrophoretic deposition (EPD) is employed for fabricating alumina (Al2O3)-based hydrogen barrier coatings, it becomes customary to enhance the adhesion strength by subjecting the deposited coating to high-temperature annealing. In this study, a functionally-graded Al2O3/ZrO2 coating was designed by using the thermal stress module of Ansys software. The influence of different gradient composition distribution indices, number of layers, and layer thickness on the distribution of thermal stress was systematically investigated by simulation. Based on simulation results, the gradient parameters of the functionally-graded coating were determined as follows: a transition layer with three layers, each with a thickness of 0.13 mm; the first layer consisted of Al2O3 to ZrO2 ratio of 1:3, the second layer with a ratio of 1:1, and the third layer with a ratio of 3:1. Subsequently, the process parameters for EPD of Al2O3 coating were optimized via experimental exploration. Under conditions of deposition time of 120 s, deposition voltage of 60 V, Al2O3 concentration of 8 g L−1 in the electrophoretic solution, and magnesium chloride hexahydrate concentration of 0.6 g L−1, the as-fabricated Al2O3 coating exhibited optimal hydrogen barrier performance. Finally, different proportions of ZrO2 were sequentially incorporated into the prepared Al2O3 coating to form functionally-graded materials (FGM). Thermal cycling experiments showed that the Al2O3 coating with added ZrO2 exhibited better stability at high temperatures. Regarding hydrogen barrier performance, the functionally-graded coating outperformed the non-functionally-graded coating.