Multilayer gradient rare earth disilicate coating prepared by in-situ melt infiltration and sintering method with high thermal shock resistance on porous Si3N4 ceramics

Dense multilayer gradient rare earth disilicate (γ-Y2Si2O7 /β-Yb2Si2O7 /β-Lu2Si2O7) coatings were in-situ prepared by melt-infiltration /sintering procedure on porous Si3N4 ceramics for water resistance. Experimental and numerical simulation methods were used to study their thermal shock behavior. As a control, thermal shock behavior of pure γ-Y2Si2O7 coatings were also compared. FEM results showed that the gradient design of modulus in ceramic coating can effectively avoid the mismatch of mechanical properties between coating layer and internal substrate, reducing the transient thermal stress in each layer during thermal shock. All of the pure γ-Y2Si2O7 coatings were failed after thermal shock tests with ΔT ≈ 1200 ℃. However, when sintering temperature of multi-layer disilicate coatings were higher than 1400 ℃, the water absorption rates after thermal shock were all less than 5%, still showing good waterproof performance. The gradient design of modulus could effectively improve the structural stability of ceramic coatings.