Effect of phase transformations on the fracture toughness of t′ yttria stabilized zirconia

The influence of temperature gradient across YSZ on thermal cyclic lifetime of plasma-sprayed thermal barrier coatings

“…It was reported that when temperature exceeds 1200 1C [21], the phase transformation of YSZ from the non-transformable tetragonal (T´) phase to monoclinic (M) phase may occur and therefore deteriorate the durability of TBCs [24][25][26]. Hence, the phase compositions of YSZ before and after the thermal cycling test were investigated.…”

Phase and fracture toughness evolution during isothermal annealing of spark plasma sintered zirconia co-doped with Yb, Gd and Nd oxides

“…This is in agreement with the cubic phase evolution in stabilized zirconia e.g., 8YSZ EBPVD coating upon annealing, spark plasma sintered 8 mol.% YbO 1.5 stabilized ZrO 2 (8YbSZ) pellet upon isothermal annealing and 8YSZ pellet upon isothermal annealing. [9][10][11] The 12 h sample contains cubic phase with a volume fraction of 11.26% and two tetragonal phases. The precipitation of the cubic phase proceeds further and it reaches a volume fraction of 19.25% after 48 h.…”

“…[1][2][3][4][5][6][7][8][9] It has recently been shown that the fracture toughness of t zirconia is linked to the phases present in the material. 10,11 The high initial indentation toughness decreases rapidly at the onset of partitioning of the t phase at a temperature like 1250 • C, and the toughness is recovered subsequently over prolonged thermal exposure of 192 h. Ferroelastic toughening is mainly responsible for the high indentation toughness of t zirconia. 10,11 The magnitude of fracture toughness enhancement is given by 12,13 Γ = 2f s hτ c γ (1) where f s is the volume fraction of the material in the process zone around the crack tip that experiences ferroelastic switching.…”

“…10,11 The high initial indentation toughness decreases rapidly at the onset of partitioning of the t phase at a temperature like 1250 • C, and the toughness is recovered subsequently over prolonged thermal exposure of 192 h. Ferroelastic toughening is mainly responsible for the high indentation toughness of t zirconia. 10,11 The magnitude of fracture toughness enhancement is given by 12,13 Γ = 2f s hτ c γ (1) where f s is the volume fraction of the material in the process zone around the crack tip that experiences ferroelastic switching. process zone width is h, while τ c is the critical stress and γ is the strain associated with ferroelastic switching.…”

Error and modification in thermal barrier coatings measurement using impedance spectroscopy

“…During service of gas turbines, TBCs is subjected to high temperature exposure, sintering and corrosion, which can lead to a change in the microstructure for TBCs, such as, the formation and growth of thermally grown oxide (TGO) at interface, phase transformation, porosity decrease in coating [3][4][5] The TGO formation results in a large compressive stress, which leads to TGO undulation, crack formation, propagation, coalescence and eventually top ceramic coating spallation [6,7]. Phase transformation, such as, the metastable t' phase undergoes transformations, changing from t' YSZ into monoclinic (m) YSZ, which results in a volume expansion in TBCs [8]. The porosity decrease in a top ceramic coating reduces the strain tolerance, which is detrimental to the lifetime of thermal cycling [9].…”