On June 28, 2023, a team from the Graduate School of Engineering at the University of Tokyo announced that they had developed a high-strength zirconia ceramic that subverted the concept of ceramics and exhibited high toughness comparable to metals. In addition to the high-strength material market, it is expected to be used in a wide range of fields requiring high reliability.

Research Background

High-strength zirconia is a fine ceramic known as a representative structural ceramic and is widely used in dental materials, crushing balls, decorative materials, optical fiber connectors, industrial equipment materials, etc. Their strength and toughness are strongly controlled by the stability of the crystal phases that make up the microstructure, and the strengthening mechanism is understood through stress-induced phase transitions.

High-strength zirconia has good mechanical properties, but its toughness is not as good as that of metal materials. Because strength and toughness are often traded off against each other, it is difficult to achieve high toughness comparable to that of metals without reducing strength. Therefore, based on the strengthening mechanism of zirconia, scientists proposed a microstructure hypothesis to overcome brittleness.

Research progress

The Engineering Research Group of the Graduate School of the University of Tokyo is working on the preparation of tetragonal zirconia (1.5Y) with a yttrium oxide content of 1.5 mol%, which is considered difficult to obtain high-strength zirconia. The zirconia powder dissolved in the solid was hydrolyzed to synthesize yttrium, and its sintering behavior was investigated. It was found that high-density tetragonal zirconia composed of fine grains could be obtained at 1300-1400 °C.

After sintering at 1400 °C, grains formed uniformly and yttrium was uniformly present in the grains, verifying that tetragonal zirconia with low yttrium oxide concentration can be obtained by controlling the assumed microstructure. Next, in order to study the effect of this microstructure, the scientists evaluated the mechanical properties of 1.5Y sintered at 1400°C. Compared with conventional high-strength zirconia with a yttrium concentration of 3mol%, the toughness increased by nearly 4 times.

Microstructure Analysis of 1.5Y Sintered at 1400°C

Scientists further investigated the effect of trace amounts of alumina doping, doped 1.5Y with 1mol% alumina, and processed thermal isotropic pressure at 1350 °C, and finally increased the bending strength to 1500 MPa without reducing toughness. When comparing the properties of the material, scientists found that the zirconia developed this time has a high toughness comparable to that of metals, far exceeding the toughness of 3Y and other ceramics.

Mechanical properties

Compared with conventional high-strength zirconia, the zirconia material developed by the University of Tokyo this time has not only toughness but also excellent deterioration resistance, so it is expected to accelerate the market growth of high-strength materials and expand to a wide range of applications requiring high reliability. field.