Yttria stabilized zirconia (YSZ) is an attractive biomaterial with excellent properties, but its deformation mechanism under repetitive loads is still unclear. In this study, the subsurface microstructural changes of YSZ polycrystals under repetitive loading/unloading were investigated by multi-cyclic nanoindentation. Raman spectroscopy analysis revealed that a tetragonal-to-monoclinic (t-m) phase transformation occurred, and multi-cyclic indentation promoted this transformation significantly. Cross-sectional scanning transmission electron microscopy showed that monoclinic variants were extensively generated beneath the free surfaces outside the indent planes, whereas grain refinement was dominant beneath the indenter tip. In addition, load-displacement curve analysis demonstrated that the t-m phase transformation occurred during unloading rather than loading, and that the phase transformation-induced volume expansion caused an incremental change of residual indent depth. The extension of monoclinic variants was promoted by repetitive shear deformation, resulting in significant pileups, as detected by atomic force microscopy. The effect of sample surface preprocessing on indentation behaviors was also investigated. Microcracking and surface spalling were confirmed around the multi-cyclic indents made on diamond-turned YSZ samples. Based on the experimental results, a model of subsurface microstructure distribution and evolution was established. The findings from this study help clarify the historical effects in subsurface damaging mechanism of brittle polycrystalline materials caused by cyclic tool-workpiece interactions in nanoscale mechanical processing.

氧化钇稳定的氧化锆（YSZ）是一种有吸引力的生物材料，具有出色的性能，但在重复载荷下其变形机理仍不清楚。在这项研究中，通过多循环纳米压痕研究了YSZ多晶在重复加载/卸载下的表面微观结构变化。拉曼光谱分析表明发生了四方相到单斜相（tm）的相变，并且多环压痕显着促进了这种相变。横截面扫描透射电子显微镜显示，单斜变体广泛产生于压痕平面外部的自由表面之下，而晶粒细化在压痕尖端下方占主导。此外，载荷-位移曲线分析表明，tm相变发生在卸载而不是加载过程中，并且相变引起的体积膨胀导致残余压痕深度的增量变化。反复剪切变形促进了单斜变体的扩展，如原子力显微镜检测到的那样，导致大量堆积。还研究了样品表面预处理对压痕行为的影响。在金刚石车削的YSZ样品上制作的多环压痕周围证实了微裂纹和表面剥落。根据实验结果，建立了地下微结构的分布和演化模型。