A polycrystalline model is proposed in this work for hydroxyapatite (HAp) to study its microstructures and mechanical properties, as well as their variations with grain size. The polycrystalline HAp (pHAp) consists of grains with a controllable size distribution. In the equilibrium structures that are relaxed with a simulated annealing method, the boundary atoms mismatch in a disordered pattern in the interfacial region. In contrast to its crystal structure, pHAp is characterized by its isotropy in mechanical properties. The elastic constants and moduli of pHAp are in general smaller than those of crystal HAp and increase with grain size, following the reverse Hall-Petch relationship. Moreover, the uniaxial tension simulations reveal that pHAp has similar stress-strain relationship in the x, y and z directions. An elastic deformation is noted at 0–2% strain, followed by a plastic deformation at 2–20% strain, which is distinct from the brittle fracture in crystal HAp. The maximum stress of pHAp decreases with decreasing grain size. A good linear dependence is noted by fitting the maximum stress and inverse square root of average grain size. Our simulations demonstrated that compared to crystal HAp, pHAp with ultra-fined grain sizes exhibits good ductility but moderate mechanical strength. Our findings would be helpful for the design of HAp-based biomaterials with controllable microstructures and mechanical performances.

在这项工作中，提出了一种针对羟基磷灰石（HAp）的多晶模型，以研究其微结构和力学性能以及它们随晶粒尺寸的变化。多晶HAp（pHAp）由尺寸分布可控的晶粒组成。在通过模拟退火方法松弛的平衡结构中，界面原子在界面区域中以无序模式失配。与它的晶体结构相反，pHAp的特点是机械性能各向同性。通常，pHAp的弹性常数和模量小于晶体HAp的弹性常数和模量，并随霍尔-Petch关系的相反而随晶粒尺寸增加。此外，单轴张力模拟表明，pHAp在x，y上具有相似的应力-应变关系。和z方向。在0–2％应变时会出现弹性变形，然后在2–20％应变时会发生塑性变形，这与晶体HAp的脆性断裂不同。pHAp的最大应力随着晶粒尺寸的减小而减小。通过拟合最大应力和平均晶粒尺寸的平方根反比，可以发现良好的线性相关性。我们的模拟表明，与晶体HAp相比，具有超细晶粒尺寸的pHAp具有良好的延展性，但机械强度适中。我们的发现将有助于设计具有可控的微观结构和机械性能的基于HAp的生物材料。