热激励下KDP晶体金刚石切削的微塑性域材料去除机理研究

In major national optical projects, such as the Inertial Confinement Fusion and the Ultra-Short Pulse Laser, a large number of KH2PO4(KDP) crystal optical components achieve ultra-precision surfaces by diamond turning. However, defects of current machining quality, especially the inefficiency and surface damages due to the brittleness of KDP crystals, are still the key technical problems restricting developments of the optical projects mentioned above. Begin with exploration of affection laws in temperature changes to KDP crystal, this project analysis temperature distribution under thermal excitation at first. Then, relationship among factors: such as surface roughness、spot diameter and power of the heat source with the rate of temperature change can be established. On this basis, brittle-ductile transition process and growth of micro-ductile domain are studied by use of nano-scratch tester and atomic force microscopy under different temperature distributions. At the same time, through diamond turning experiments, thermo-dynamic behavior in material removal process of KDP crystal and the recognition of the critical cutting thickness are researched. Ultimately, the mechanism of material removal and precision creation in the mico-ductile domain of KDP crystal by diamond turning are revealed. Absolutely, achievements of this project not only help to improve the efficiency and surface quality of the KDP crystal in diamond turning, but also contribute to enrichment of the ultra-precision machining basical theory.

在惯性约束核聚变和超短脉冲激光器国家重大光学工程中，大量磷酸二氢钾（KDP）晶体光学元件需要采用金刚石切削来实现超精密加工。但目前的切削加工质量，尤其是该材料脆性带来的低效和表面缺陷问题仍是制约上述光学工程发展的关键技术难题。本项目从探索温度变化对KDP塑性切削的作用规律入手，分析KDP晶体在热源激励下的耦合温度场分布，明确表面粗糙度、热源光斑直径和功率等因素与温度变化速率的关系。在此基础上，采用纳米划痕仪和原子力显微镜在微观尺度上研究KDP晶体表面脆塑转变过程与微塑性域随温升的增长规律。结合金刚石切削实验，研究在不同温度场下KDP晶体材料去除热力学行为，并完成临界切削厚度的状态辨识。最终揭示在热激励下的KDP晶体金刚石切削微塑性域材料去除机理和精度创成机制。本课题研究成果不仅有助于提升KDP晶体金刚石切削的效率和表面质量，也将为丰富超精密加工的基础理论做出贡献。

本课题以探索KDP 晶体高效率、超精度和高稳定性金刚石切削（SPDT）加工问题为核心，从温度变化对KDP切削的作用规律入手，系统开展了热激励下的KDP 晶体金刚石微塑性域切削材料去除机理研究。首先，通过实验测试掌握了在环境温度、切削热和辅助热源耦合作用下，KDP 晶体SPDT 表面复合温度场分布规律。然后，采用纳米压/划痕的方法明确了KDP晶体表面硬度、断裂韧度、临界切削厚度随温度分布的变化规律。在此基础上，基于实验和数值模拟结果获得了KDP 晶体表面脆塑转变临界切削状态，揭示了复合温度场下的KDP晶体金刚石切削微塑性域材料去除机理。最后，搭建了KDP 晶体热激励作用下SPDT 工艺实验平台，解决了KDP晶体受热不均匀导致的内部裂纹等难题，通过工艺实验完成了工艺参数的优化匹配。加工实验结果表明：相比于常温，在一定的热源作用下，KDP 晶体表面粗糙度和疵病的均有一定程度的减小。上述研究成果为提升KDP晶体表面SPDT的加工质量探索了一条新途径，亦可为类似难加工光学晶体材料的超精密单点金刚石切削加工提供借鉴。