The Effect of Sintering Temperature on Phase-Related Peculiarities of the Microstructure, Flexural Strength, and Fracture Toughness of Fine-Grained ZrO2–Y2O3–Al2O3–CoO–CeO2–Fe2O3 Ceramics

Abstract

The lifetime of products made of ceramic materials is related to their mechanical characteristics such as strength, hardness, wear resistance, and fracture toughness. The purpose of this work was to study the effect of sintering temperature on the phase-related peculiarities of the microstructures, causing changes in the flexural strength and fracture toughness of fine-grained ZrO2–Y2O3–Al2O3–CoO–CeO2–Fe2O3 ceramics. Flexural strength and fracture toughness tests were carried out using ceramics sintered in three modes (2 h at 1550 °C, 1580 °C, and 1620 °C in argon), and thorough phase, microstructure, and fractographic analyses were performed. For the ceramic sintered at 1550 °C, a mixed mechanism of intergranular fracture of the t-ZrO2 phase particles and cleavage fracture of the Ce–Al–O phase particles was found, which is reflected in its comparatively low fracture toughness. For the ceramic sintered at 1580 °C, a fracture developed along the boundaries of the aggregates, made of completely recrystallized fine ZrO2 grains with a high bond strength between adjacent t-ZrO2 grains; this corresponds to the highest fracture toughness (5.61 ± 0.24 MPa·m1/2) of this ceramic. For the ceramic sintered at 1620 °C, a transgranular fracture of the t-ZrO2 phase and Ce–Al–O phase particles and crack propagation along the t-ZrO2/Ce–Al–O interface were revealed; this caused a decrease in fracture toughness.