氧化锆纳米压入相变行为及其形变分子动力学研究

发布时间：2018-05-13 16:39

本文选题：氧化锆 + 纳米压入　；参考：《太原理工大学》2017年硕士论文

【摘要】：氧化锆陶瓷因其具有高强度、高硬度和相变增韧等特性,已成为一种重要的工程材料,而其力学行为及变形机理成为相关学者研究的热点。本文基于纳米压入实验方法研究了氧化锆(Ce-TZP)陶瓷在压入过程中相变与其力学性能的关系,并通过分子动力学方法模拟了压入过程中压头尖端单斜氧化锆晶体的变形行为过程,对其变形过程中的原子组态和原子位错的变化情况进行了研究。(1)在连续刚度测量模式下,分别在不同应变率下等压入深度和等应变率不同压入深度条件下对Ce-TZP进行了纳米压入测试,根据Reuss理论推导出一种确定纳米压入过程中Ce-TZP中单斜相体积分数的方法,并结合XRD分析验证了其可靠性。结果表明,受压入过程中相变行为的影响,在加载阶段氧化锆表现出一定的应变率敏感性,相变增韧机制对其力学性能有显著影响;而其弹性模量的改变主要受t→m相变过程中所形成的单斜相影响,弹性模量和单斜相体积分数随着压入深度增加而呈相反的规律。在相同压深条件下,单斜相体积分数随着应变率增加而降低。(2)在Lewis等提出的对势理论和Wolf等提出的系统库伦势能理论的基础上建立氧化锆单斜晶体的分子动力学模型,用以模拟纳米压入实验过程中压头尖端单斜相氧化锆的变形及力学行为。结果表明压入过程中产生的载荷波动是由基体内部原子堆垛和位错变化引起;对单斜相晶体不同方向的压入会在其内部产生不同的滑移面,且在压入过程中载荷间断下降的原因也不相同。不同压入速率下载荷位移曲线在弹性段重合,在塑性段展现了一定的率相关性特征;低压入速率下由于应力驰豫P-h曲线会表现出明显的应变硬化和载荷波动现象。
[Abstract]:Zirconia ceramics have become an important engineering material because of its high strength, high hardness and phase transformation toughening. The mechanical behavior and deformation mechanism of zirconia ceramics have become the focus of research. In this paper, the relationship between phase transition and mechanical properties of Zirconia Ce-TZP ceramics during indentation is studied based on the experimental method of nano-indentation. The deformation behavior of monoclinic zirconia crystal at the tip of the indenter is simulated by molecular dynamics method. The atomic configuration and the change of atomic dislocation in the deformation process are studied. Nano-indentation tests of Ce-TZP were carried out under the condition of equal indentation depth and equal strain rate at different strain rates. According to Reuss theory, a method for determining monoclinic volume fraction in Ce-TZP was deduced. The reliability is verified by XRD analysis. The results show that the zirconia exhibits a certain strain rate sensitivity during loading, and the toughening mechanism of phase transition has a significant effect on the mechanical properties of zirconia. The change of elastic modulus is mainly affected by the monoclinic phase formed during the t m phase transition. The elastic modulus and the volume fraction of monoclinic phase show the opposite law with the increase of indentation depth. Under the same pressure condition, the monoclinic phase volume fraction decreases with the increase of strain rate. The molecular dynamics model of zirconia monoclinic crystal is established on the basis of the counter potential theory proposed by Lewis et al and the system Coulomb potential energy theory proposed by Wolf et al. The deformation and mechanical behavior of monoclinic zirconia at the tip of the head were simulated. The results show that the load fluctuation in the process of indentation is caused by the changes of atoms stacking and dislocations in the matrix, and the different slip planes are produced in the different directions of the monoclinic crystals. The reasons for the continuous decrease of load in the process of indentation are also different. The loading displacement curve of different indentation rates overlapped in the elastic section and showed a certain rate correlation in the plastic section, and the P-h curve showed obvious strain hardening and load fluctuation phenomenon at low pressure entry rate due to stress relaxation.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ174.1

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