Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK.
Acta Biomater. 2013 Apr;9(4):6226-35. doi: 10.1016/j.actbio.2012.11.027. Epub 2012 Dec 3.
Zirconia has been used as an orthopaedic material since 1985 and is increasingly used in dental applications. One major concern with the use of zirconia is the significant loss in mechanical properties through hydrothermal degradation, with the uncontrolled transformation of tetragonal to monoclinic (t→m) zirconia. We report on the addition of alumina and lanthana as dopants to an yttria-stabilized tetragonal zirconia polycrystal ceramic as an effective strategy to significantly decelerate the hydrothermal degradation kinetics, without any loss of mechanical properties, in particular, fracture toughness. Hydrothermal degradation was studied on the exposed surface as well as in the sub-surface region using Raman microspectroscopy, atomic force microscopy and cross-sectional transmission electron microscopy, providing a comprehensive insight into the mechanism of propagation of the t→m transformation. The addition of dopants resulted in the reduction of monoclinic zirconia nucleation rate at the surface and a substantial deceleration of the overall transformation kinetics, in particular a greatly reduced propagation of the transformation into the bulk and decreased grain boundary microcracking. High-resolution transmission electron microscopy analysis showed that the co-dopant cations segregate to the grain boundaries where they play a key role in the stabilization of the zirconia tetragonal phase.
氧化锆自 1985 年以来一直被用作骨科材料，并且越来越多地用于牙科应用。氧化锆的一个主要问题是通过湿热降解导致机械性能显著损失，其中四方相到单斜相（t→m）的氧化锆无控制转变。我们报告了在氧化钇稳定四方氧化锆多晶陶瓷中添加氧化铝和镧作为掺杂剂，这是一种有效策略，可以在不损失机械性能（特别是断裂韧性）的情况下，显著减缓湿热降解动力学。使用拉曼微光谱仪、原子力显微镜和横截面透射电子显微镜研究了暴露表面和亚表面区域的湿热降解，提供了对 t→m 转变传播机制的全面了解。掺杂剂的添加导致表面四方氧化锆形核速率降低，并且整体转变动力学大大减慢，特别是转变向体相的传播大大减慢，晶界微裂纹减少。高分辨率透射电子显微镜分析表明，共掺杂阳离子在晶界处偏析，在稳定氧化锆四方相方面发挥着关键作用。
