Department for Nanostructured Materials, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
Engineering Ceramics Department, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
Acta Biomater. 2017 Oct 15;62:306-316. doi: 10.1016/j.actbio.2017.08.014. Epub 2017 Aug 12.
The yttrium-segregation-dependent phase partitioning and residual stress development that influence both the aging and the fracture behaviour in 3Y-TZP bioceramics were studied by sintering alumina-free 3Y-TZP, varying the sintering temperature and the time, to yield ceramics with identical grain size distributions, but with different phase compositions. The structure and stability of the resulting tetragonal phases, in the form of transformable, yttria-lean t-ZrO (YLZ) and non-transformable, yttria-rich t″-ZrO and/or t'-ZrO (YRZ), were studied by X-ray diffraction (XRD) and focused ion beam scanning electron microscopy (FIB-SEM). The accelerated aging kinetics was fitted to the Mehl-Avrami-Johnson equation. The specimen sintered at the lowest sintering temperature but with the longest dwell time contained the smallest and the largest concentrations of yttria in the YLZ and YRZ phases, respectively, as well as the largest amount of YRZ. As a consequence, it exhibited the fastest linear aging kinetics accompanied by more extensive micro-cracking of the transformed layer, as well as largest amount of intergranular fracture and the greatest resistance to fracture. These properties were ascribed to the increased transformability of the YLZ phase and the greatest propensity of the YRZ phase to relax the accumulated residual stresses during transformation (tetragonal to monoclinic, t-m) manifested asa∼2.4% unit-cell volume increase. The observed relaxation provides additional understanding of the t-m transformation mechanism, which governs both the aging and fracture behaviour of 3Y-TZP.
A novel approach to understanding the effect of yttrium segregation on t-m transformation of 3Y-TZP zirconia bioceramics is presented. Carefully designed sintering strategy facilitated fabrication of ceramics with identical grain size distributions but with different yttrium concentrations. The influence of phase partitioning on stability and structure of transformable yttria-lean tetragonal phase (YLZ) and non-transformable yttria-rich phases (YRZ; t″- and t'-prime) and on the formation of residual stresses in YRZ were investigated. It is shown that YRZ phases are under compressive stresses in YLZ matrix, since a systematic relaxation after ageing was observed and explained for the first time. It puts additional perspective on the understanding of the t-m transformation mechanism ultimately governing both the ageing and fracture behaviour of 3Y-TZP.
研究了钇偏析依赖性相分离和残余应力发展对 3Y-TZP 生物陶瓷时效和断裂行为的影响，通过烧结不含氧化铝的 3Y-TZP，改变烧结温度和时间，得到具有相同晶粒尺寸分布但具有不同相组成的陶瓷。通过 X 射线衍射（XRD）和聚焦离子束扫描电子显微镜（FIB-SEM）研究了转化型富钇的 t-ZrO（YLZ）和非转化型富钇的 t″-ZrO 和/或 t′-ZrO（YRZ）以及稳定的四方相的结构和稳定性。用 Mehl-Avrami-Johnson 方程拟合加速时效动力学。在最低烧结温度但最长保温时间下烧结的试样，YLZ 和 YRZ 相中分别含有最小和最大浓度的氧化钇，以及最大量的 YRZ。因此，它表现出最快的线性时效动力学，并伴随着转化层更广泛的微裂纹，以及更多的晶间断裂和最大的抗断裂能力。这些特性归因于 YLZ 相的可转化性增加和 YRZ 相在转化过程中（四方到单斜，t-m）释放积累残余应力的倾向最大，表现为约 2.4%的单位细胞体积增加。观察到的弛豫提供了对 t-m 转变机制的进一步理解，该机制控制着 3Y-TZP 的时效和断裂行为。
提出了一种理解钇偏析对 3Y-TZP 氧化锆生物陶瓷 t-m 转变影响的新方法。精心设计的烧结策略有助于制备具有相同晶粒尺寸分布但不同钇浓度的陶瓷。研究了相分离对可转化的贫钇四方相（YLZ）和不可转化的富钇相（YRZ；t″-和 t′-prime）的稳定性和结构以及 YRZ 中残余应力的形成的影响。结果表明，在 YLZ 基体中，YRZ 相处于压应力状态，因为首次观察到并解释了老化后的系统弛豫。这为理解 t-m 转变机制提供了额外的视角，最终控制着 3Y-TZP 的时效和断裂行为。
