Composition-microstructure-mechanical property relationships and toughening mechanisms of GdPO4-doped Gd2Zr2O7 composites

Rare earth zirconates are technologically important and among the most extensively studied ceramics, but their practical applications are limited by the brittle behavior. This work investigates the mechanical properties and toughening mechanisms of GdPO4 doped Gd2Zr2O7, attempting to provide a deep understanding of composition microstructure-property relationships to optimize the composite composition. The GdPO4 existed as a second phase (reinforcement) in the matrix, which refined Gd2Zr2O7 grains, strengthened grain interfaces, and introduced residual stress in the composites. With the increase of the dopant content, the GdPO4 grains coarsened, and the generated tensile stress in the second phase decreased. At low dopant contents <30 mol%, the toughness of composites increased without sacrificing hardness and Young's modulus; but higher doping led to decreases in these properties. The strengthened interfaces, and cracks deflection, bridging and bifurcation in GdPO4 grains resulting from the layer structure and the generated tensile stress contributed to the initial increase in the toughness; while the subsequent decreased toughness was due to the GdPO4 grain coarsening.