Visualization of transformation toughening of zirconia ceramics during dynamic fracture

Establishing a mechanistic understanding of dynamic fracture is critical for the design of efficient and safe structural materials. Transformation toughening describes the process by which a crystal structure change can reduce the crack-driving force. The understanding of the dynamic behavior of transformation-toughened materials is limited. To clarify the relationship between crystal structure transformations and toughening during a dynamic loading, we carried out a time-resolved x-ray diffraction study of yttria-stabilized tetragonal zirconia polycrystal under shock loading. The results show that the ambient tetragonal crystal structure is maintained on loading and phase transformation to the monoclinic phase occurs only after the onset of dynamic fracture, indicating that the transformation toughening is associated with dynamic fracture caused by wave interactions. This study not only revealed the reason for the high spall strength of zirconia ceramics but also demonstrated the great potential for time-resolved x-ray diffraction method to study fracture dynamics.