The phase stability of t-ZrO2 realized by grain size at cryogenic temperature in ZrO2/TiO2 composite

Abstract

In this work, the trade-off between transformation toughening of ZrO2/TiO2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO2 (dt-ZrO2). A negative correlation between dt-ZrO2 and phase transition temperature (Ms) was also established based on strain energy and chemical free energy in ZrO2/TiO2 ceramic coatings. Interestingly, t-ZrO2 grains lost toughening effects when the dt-ZrO2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the dt-ZrO2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (011) t-ZrO2 and (110) TiO2 was enhanced and t-ZrO2 was completely stabilized when dt-ZrO2 reaches critical size. This work elucidates the effect of size effect on Ms and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature.