Visualizing how zirconia ceramics toughen under shock

Among crack resistant materials, zirconia ceramics, such as the 3% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), are known for their strength and toughness. Despite its known applications, the toughening mechanism of 3Y-TZP during dynamic loading is poorly understood.

Takagi et al. conducted shock wave experiments to observe the crystal structure change in 3Y-TZP that leads to its toughening. While previous calculations using numerical models have attributed 3Y-TZP’s resistance to cracking to a phase change from tetragonal to monoclinic, the group’s data indicated the transition does not occur instantaneously, but experiences a time delay until the shock is unloaded. It is not until after the material exhibits spallation fracture that the phase transformation occurs and impedes the crack-driving forces.

To obtain these time-resolved measurements of the transformation, the authors used a laser to drive a shock wave in a 3Y-TZP sample, and took X-ray diffraction images of the system at a time delay during the shock. In each successive measurement, they used a fresh sample and extended the delay slightly, allowing them to reconstruct a visualization of the transformation and its timing.

“Zirconia ceramics have already been used in real-life applications, because their high strength and toughness are well known,” said author Sota Takagi. “However, I think the deep and accurate understanding of the toughening mechanism is important to use to design the material and find better materials in the future.”

Though the present work contributes to understanding fundamental properties of zirconia ceramics, Takagi noted the study’s spatial resolution is low. For application in practical materials, high spatial resolution observations of the shock recovery process will be needed.

Source: “Visualization of transformation toughening of zirconia ceramics during dynamic fracture,” by Sota Takagi, Koji Inukai, Nobuaki Kawai, Shunsuke Nozawa, Atsushi Kyono, Ryo Fukaya, Shin-ichi Adachi, and Kouhei Ichiyanagi, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0044607 .