Abstract
The superior fracture toughness of zirconia is closely correlated with stress-induced martensitic phase transformation around a crack tip. In this study, a modified phase field (PF) model coupling phase transformation and fracture is proposed to study the fracture behavior and toughening effect of tetragonal zirconia polycrystal (TZP). The stress-induced tetragonal to monoclinic (t–m) phase transformation around a static or propagating crack is characterized with PF simulations. It is shown that the finite size and shape of the transformation zone under different loads and ambient temperatures can be well predicted with the proposed PF model. The phase transformation may decrease the stress level around the crack tip, which implies the toughening effect. After that, crack propagation in TZP is studied. As the stress field is perturbed by the phase transformation patterns, the crack may experience deflection and branching in the propagation process. It is found that the toughness of the grain boundaries (GBs) has important influences on the crack propagation mode. For TZP with strong GBs, the crack is more likely to propagate transgranularly while, for TZP with weak GBs, intergranular crack propagation is prevalent. Besides that, the crystal orientation and the external load can also influence the topology of crack propagation.
Highlights
Zirconia ceramics possess many superior mechanical properties such as high strength and toughness, excellent wear resistance, etc
The excellent mechanical properties of zirconia ceramics originate from the stress-induced tetragonal to monoclinic (t–m) martensitic transformation in the high-stress concentration zone around a crack tip
Asphase the load is axisymmetric with respect to To theshow crackthe plane, theofcrack tends to propagateon in crack mode propagation, the distribution of the horizontal normal stress σ in front of the crack tip is plotted in
Summary
Zirconia ceramics possess many superior mechanical properties such as high strength and toughness, excellent wear resistance, etc. Mamivand et al [44,45,46] developed a PF model to characterize the phase transformation process in tetragonal zirconia, which was later extended to study the temperature effect and grain size effect on the mechanical responses of TZPs under tension and compression [47]. In our previous work [39], a coupled PF model was developed to study the fracture behavior of single crystalline tetragonal zirconia [39], which was later extended to investigate intergranular microcracking in the hydrothermal degradation process [40]. The effect of the fracture toughness of the GB, the crystal orientation, and the magnitude of the external load on the topology of crack propagation are studied.
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