多晶铈金刚石刀具加工表层与亚表面损伤层形成机理研究

Ultra-smooth surface is one critical issue that influences applications and related performance of nuclear materials. Metallic cerium has been used as one important surrogate for nuclear materials. Metallic cerium undergoes multiple phase transitions under high pressure or at high temperature, and the material removal mechanisms are also different for individual phases. Furthermore, phase transition is generally combined with plastic flow in the inelastic deformation of polycrystalline cerium. Consequently, the single point diamind turning of polycrystalline cerium exhibits strong heterogeneous characteristics, which leads to the difficulty in achieving an uniform machined surface quality. In this project, we utilize molecular dynamics simulations and experiments to investigate the generation mechanisms of surface layer and subsurface damage layer in single point diamond turning of polycrystalline cerium, from below three aspects: 1) Elucidating the underlying mechanisms associated with the influence of diamond cutting on the phase transition of metallic cerium; 2) Investigating the cutting mechanisms of polycrystalline cerium subjected to the single point diamond turning; 3) Establishing a prediction model of subsurface damage layer induced in the single point diamond turning of polycrystalline cerium. The research work presented in this project will reveal the fundamental cutting mechanisms and achieve the ultra-smooth surface of polycrystalline cerium, which is thus of significant theoretical importance and practical value for guiding the fabrication of ultra-smooth surface of polycrystalline cerium by the single point diamond turning technique. These findings in this project will also serve as valuable references for the ultra-precision machining of metallic plutonium, which has similar physical and chemical properties and phase transition characterstics with metallic cerium.

超光滑表面是影响核能材料使用性能的一个关键因素。金属铈是核能领域一种重要的模拟研究材料。金属铈在高温高压下具有多相变特性，不同相态的材料去除方式也不同，并且在非弹性变形中相变与塑性流动存在耦合关系，导致多晶金属铈的单点金刚石切削加工呈现出强烈的非均向特性，难以获得均匀的加工表面质量。本项目采用分子动力学仿真与实验手段从三个方面来研究多晶铈金刚石刀具加工表层和亚表面损伤层形成机理：（1）揭示金刚石刀具切削加工对金属铈表面相结构的影响及机理；（2）研究多晶金属铈单点金刚石切削加工变形机理；（3）建立一种多晶金属铈单点金刚石切削加工亚表面损伤层定量预测技术。本项目的研究将揭示多晶金属铈的加工变形机理并获得其超光滑表面，对于使用单点金刚石刀具切削加工制备金属铈超光滑表面具有重要的理论意义与实用价值，同时对于具有与金属铈相似物理与化学性质、体相结构和相变性质的金属钚超精密加工具有重要的借鉴价值。

本项目首先采用分子动力学仿真与实验手段从三个方面来研究多晶铈金刚石刀具加工表层和亚表面损伤层形成机理：（1）金属铈各相机械属性的分子动力学仿真研究，包括确定原子相互作用的经验势能函数，创建具有不同晶体结构的金属铈各相的原子结构及其机械性能表征、开发后处理算法等；（2）开展了金属铈单点金刚石切削加工表层形成机理的分子动力学仿真研究，包括建立切削加工的分子动力学仿真模型、研究金属铈加工表层形成机理、加工表面质量评价等；（3）开展了金属铈超光滑加工表面的最优切削工艺参数的分子动力学仿真研究，获得了对应金属铈超光滑加工表面的最优切削工艺参数。分子动力学仿真结果显示金属铈的切削加工变形主要由位错运动主导，因此本项目接着采用有限元仿真来研究多晶铈金刚石切削加工工艺参数：（1）开展金属铈拉伸试验获得有限元仿真中用于描述金属铈的Johnson-Cook本构方程的参数，并据此建立金属铈金刚石切削加工的有限元仿真模型；（2）采用二维和三维有限元仿真来研究典型加工参数对金属铈切削加工的影响规律，据此获得优化的加工参数；（3）开展金属铈防氧化试验和金刚石切削加工实验，验证了仿真得到的优化加工参数的有效性。最终得到了表面粗糙度Ra为8.4nm的金属铈超光滑表面。本项目的研究将揭示多晶金属铈的加工变形机理并获得其超光滑表面，对于使用单点金刚石刀具切削加工制备金属铈超光滑表面具有重要的理论意义与实用价值，同时对于具有与金属铈相似物理与化学性质、体相结构和相变性质的金属钚超精密加工具有重要的借鉴价值。