R-curve of La2O3 doped Zirconia Toughened Alumina Composites Prepared via Stereolithography based 3D Printing

In this study, we combined liquid precursor infiltration of high introduction amounts of bi-additives (20wt%) and stereolithography-based 3D printing to fabricate zirconia toughened alumina, and the infiltration systems consist of the four following systems Zr4+/La3+, Zr4+/Er3+, Zr4+/Gd3+, and Zr4+/Ce4+. The sample immersed with Zr4+/La3+ shows intense peaks of m-ZrO2 phase compared to the other samples while a new phase of flake-like LaAl11O18 occurs in the Zr4+/La3+ immersed sample, the existence of which could be confirmed by XRD and EDS. The fracture toughness of the Zr4+/Er3+, Zr4+/Gd3+, and Zr4+/Ce4+ samples remained basically unchanged versus the crack size, while the measured fracture toughness values for the Zr4+/La3+ system could be fitted as a rising R-curve behavior with the steady-state fracture toughness of 17.76 MPa·m1/2. The enormous enhancement of the toughness could be attributed to thermal expansion misfit and flake-like LaAl11O18 in the Zr4+/La3+ system. The effect of residual stresses on the fracture mode and thus the toughness is discussed on the basis of theoretical calculation and analysis. It is the first time a rising R-curve behavior is observed in the 3D printed ceramics. The shocking discovery provides a highly effective toughening way in 3D printing combined infiltration approach.