Interaction of Gd2Si2O7 with CMAS melts for environmental barrier coatings

Environmental barrier coatings (EBCs) prevent the oxidation of ceramic matrix composites (CMC), which are used as components in gas turbines. However, EBCs deteriorate more rapidly in real environments, molten silicate deposits accelerate the deterioration of EBCs. In this study, high-temperature behavior sintered Gd 2 Si 2 O 7 with calcia-magnesia-alumina-silica (CMAS) melt at 1400°C for 0.5, 2, 12, 48, and 100 h was investigated. HT-XRD results showed that at 1300°C, CMAS and Gd 2 Si 2 O 7 chemically reacted to form Ca 2 Gd 8 (SiO 4 ) 6 O 2 (apatite). The reaction layer became thicker as the heat-treatment time increased, and the thickness of the reaction layer has increased following a parabolic curve. With the extension of the reaction time from 0.5 to 100 h, the thickness of the reaction layer increased from approximately 98 to 315 μm. It was confirmed that Ca 2 Gd 8 (SiO 4 ) 6 O 2 grew vertically on the Gd 2 Si 2 O 7 surface. Vertical and horizontal cracks were found after reacting at 1400°C for 100 h, but no interfacial delamination occurred in this study. In addition, the effects of CaO:SiO 2 molar ratios, monosilicates (RE 2 SiO 5 ) and disilicates (RE 2 Si 2 O 7 ), heat-treatment time, and cation size were determined and compared with the results of previous studies (Gd 2 SiO 5, Yb 2 SiO 5, and Er 2 Si 2 O 7 ).