In-situ generated ferroelastic LaAlO3 toughened Y3Al5O12 composite ceramics with improved fracture toughness and thermal expansion coefficient for thermal barrier coating materials

Yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) is regarded as a candidate of thermal barrier coating material for its excellent thermal stability and corrosion resistance, yet the poor fracture toughness and the low thermal expansion coefficient are the roadblock that limits its application. In order to improve the fracture toughness and the thermal expansion coefficients, a series of Y 3 Al 5 O 12 composite ceramics toughened by ferroelastic LaAlO 3 second phase were prepared by in-situ synthesis method in this work. The prepared x LaAlO 3 /(1- x )Y 3 Al 5 O 12 composite ceramics ( x =10∼50%) exhibit superior fracture toughness (2.16 MPa·m 0.5 ∼2.63 MPa·m 0.5 ) with respect to single-phase Y 3 Al 5 O 12 (1.94 MPa·m 0.5 ), which is mainly attributed to the synergistic effects of ferroelastic toughening of second phase, residual stress toughening, and fine-grain strengthening. On the account of the synergistic effects of three toughening mechanisms, 0.2LaAlO 3 /0.8Y 3 Al 5 O 12 composite ceramic manifest the strongest fracture toughness (2.63 MPa·m 0.5 ), which is 36% improved compared with single-phase Y 3 Al 5 O 12 . In addition, the thermal expansion coefficients of x LaAlO 3 /(1- x )Y 3 Al 5 O 12 specimens (9.54∼9.97 × 10 -6 K -1 at 1200 °C) are larger than that of Y 3 Al 5 O 12 (9.25 × 10 -6 K -1 at 1200 °C). Especially, 0.5LaAlO 3 /0.5Y 3 Al 5 O 12 specimen exhibits the highest thermal expansion coefficient (9.97×10 -6 K -1 at 1200 °C), which improve by 7.78% compared to single-phase Y 3 Al 5 O 12 . The improved fracture toughness and the capable thermal expansion coefficients of LaAlO 3 /Y 3 Al 5 O 12 composite ceramics renders their promising aspect for thermal barrier coating application.