Damage Tolerance and Extensive Plastic Deformation of -Yb2Si2O7 from Room to High Temperatures

beta-Yb2Si2O7 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 -Yb2Si2O7 sample was synthesized by insitu 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/sigma provide evidences of damage tolerance of -Yb2Si2O7. -Yb2Si2O7 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 degrees C and 1300 degrees 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 degrees C.