Effects of He ion irradiation on the microstructures and mechanical properties of t' phase yttria-stabilized zirconia ceramics

The dense ZrO₂-8 wt.% Y₂O₃ ceramics with tetragonal (t') phase were prepared by spark plasma sintering (SPS). The micro-structure modification in poly-crystalline t' phase YSZ ceramics irradiated with 60 KeV He ions over a wide fluence range were studied. It is found that, the t' → t + c phase transformation was detected for the samples irradiated at the fluence above 2 × 10¹⁷ cm⁻². In addition, a three-steep model for damage stages has been proposed and discussed for interpreting the evolution of mechanical properties of t'-YSZ ceramics after irradiated, mainly revealed by the analysis from HRTEM results. Firstly, as the He⁺ fluences range from 0.5 × 10¹⁷ cm⁻² to 1 × 10¹⁷ cm⁻², the hardening effects were confirmed in t'-YSZ owing to the irradiation induced defects serve as obstacles to resist slipping of dislocations. As the fluence was increased to 2 × 10¹⁷ cm⁻², the degradation of mechanical properties was evidenced, which could be ascribed to the deterioration effect of aggregated He bubbles inside t' YSZ grains. While the fluence increased to 10 × 10¹⁷ cm⁻², a seriously damaged region was approximately located at 250 nm in depth, at which a great number of He bubbles with different shape and dislocation loops were evidenced, leading to a further reduction of hardness and elastic modulus. No micro-cracks emerge even for He⁺ fluences as high as 10 × 10¹⁷ cm⁻², indicating high irradiation stability and resistance to micro-crack propagation in t'-YSZ.