Synthesis and performance of mullite/Y2Si2O7/ZrO2 coating: Microstructure, phase evolution, and thermal shock behavior

A uniform, dense, and well-bonded mullite/Y 2 Si 2 O 7 /ZrO 2 (MYZ) composite barrier coating was synthesized using a spraying technique followed by a two-step sintering process. The microstructure, phase composition, and thermal shock resistance of the MYZ coating were systematically investigated. The sintering process comprised two stages. In the initial stage (25–1350°C), granular mullite grains transformed into columnar crystals with progressive growth. Concurrently, a eutectic composite of mullite and Y 2 Si 2 O 7 formed and dispersed within the grain boundaries, significantly enhancing the coating's density and adhesion. In the subsequent stage (∼1400°C), ZrO 2 reacted with the eutectic composite to produce yttria-stabilized zirconia (YSZ) in situ. The YSZ phase exhibited excellent interfacial compatibility with the substrate, markedly improving the coating's high-temperature stability. As a result, the coating achieved high hardness and a coefficient of thermal expansion matching that of the SiC substrate. Remarkably, the MYZ coating withstood 20 thermal cycles between 25°C and 1200°C without noticeable interfacial damage.