Damage Tolerance and Extensive Plastic Deformation of β‐Yb 2 Si 2 O 7 from Room to High Temperatures

β‐Yb 2 Si 2 O 7 is a promising environmental barrier coating ( EBC ) material and recently attracted attention for its damage tolerance. To investigate the mechanisms of its damage tolerance and possible plasticity, dense β‐Yb 2 Si 2 O 7 sample was synthesized by in situ reaction/hot‐pressing method, and its mechanical properties were measured from room to high temperatures. The low magnitudes of hardness to Young's modulus ratio H V /E , shear modulus to bulk modulus ratio G/B , and high fracture toughness to strength ratio K IC / σ provide evidences of damage tolerance of β‐Yb 2 Si 2 O 7 . β‐Yb 2 Si 2 O 7 exhibits extensive plastic deformation in Hertzian contact tests at both room and high temperatures. Transmission electron microscopy ( TEM ) observations show that the deformation mechanisms are different at low and high temperatures. Deformation twinning and parallel dislocation arrangement occur in plastic deformation at room temperature. Above the brittle‐to‐ductile transition temperature (between 1200°C and 1300°C), plastic deformation brings out extensive slip and climb of dislocations, while twinning is seldom observed. Measurement of temperature‐dependent dynamic Young's modulus demonstrates excellent elastic stiffness retention up to 1300°C.