Thermophysical and mechanical properties of cubic, tetragonal and monoclinic ZrO2

Yttrium-stabilized zirconia (YSZ) materials are routinely used as thermal barrier coatings (TBCs). The phase composition and microstructure of YSZ materials significantly influence their properties. In this study, ZrO2 ceramics composed respectively of monoclinic ZrO2 (m-ZrO2), tetragonal YSZ (t-YSZ) and cubic YSZ (c-YSZ) phases were sintered. The effect mechanism of phase composition and microstructure on thermophysical and mechanical properties were investigated by experiment together and numerical calculation. The result indicates that YSZ materials with c-YSZ phase are more suitable as TBC materials in terms of heat insulation, thermal expansion match with the metal substrate, and strain tolerance. The YSZ ceramic with c-YSZ phase also exhibits lower thermal conductivity than those composed of the t-YSZ and m-ZrO2 phases due to its greater lattice distortion, number of oxygen vacancies, and lower sound velocity as a result of greater Y2O3 doping. Bond lengths and cohesive energy calculations based on first principles reveal that the reason that the Y2O3 doping causes the CTE values of ZrO2 to increase is due to the bonding between ions becoming weaker, and the c-YSZ phase exhibits the highest CTE value. First-principles calculations also indicate that the c-YSZ phase exhibits a lower elastic modulus and better malleability and plasticity than m-ZrO2 and t-YSZ phases. However, the t-YSZ phase has better fracture toughness due to toughening under stress and finer grains.