红外多晶材料柔体抛光表面谷粒形貌的形成机理与控制方法研究

Infrared polycrystalline materials such as magnesium aluminate possess the outstanding optical performances and mechanical performances, and they are appropriate materials for infrared window and dome. But it is very difficult to machine these materials with high accuracy, and the application is greatly restricted. Especially in the machining process with compliant polishing tools, grain profiles will appear on the machined surface, which will result in the deterioration of machining accuracy, surface quality and optical performance, and the requirement can't be satisfied for optical application. Aiming at the controlling method of grain profiles on polishing surface and ultraprecision machining for infrared polycrystalline materials in this study, the forming mechanism and the evolving rule of grain profiles are analyzed, and the relation model is founded on the characteristic size of grains, the flexibility of polishing tools, the diameter of removal function and the acting forces. Based on the method of electron beam modification, the machining surface of infrared polycrystalline materials are equably modified to the extent of designed depth. Furthermore, the corresponding relation is studied between the uniformity of removal rate and the grain characteristics by applying magnetorheological finishing technology, the design algorithm for modificating layer is presented, the controlling means of grain profiles is formed, and the infrared polycrystalline materials such as magnesium aluminate is machined with high accuracy, ultrasmooth surface and micro-subsurface damage by implementing the precise figuring on machining surface. The research findings in this study can satisfy the imaging requirements of infrared guidance systems, and provide the theoretical foundation and technical support for the mass production of infrared polycrystalline windows and domes with high accuracy and low cost.

铝酸镁等红外多晶材料具有优异的光学、力学性能，是红外窗口和整流罩的理想候选材料。由于加工难度很大，其应用受到了限制；特别是在柔体抛光过程中，加工表面出现明显的谷粒状形貌，这会降低零件的加工精度和表面质量，影响光学性能，无法达到使用要求。本项目以铝酸镁等红外多晶材料抛光表面谷粒形貌的控制和高精度加工为目标，通过分析谷粒形貌的形成机理和演变规律，建立特征尺寸与抛光工具柔性、去除函数束径、作用力的关系模型；基于电子束改性方法，实现红外多晶材料表层区域在设定深度范围内的均匀改性；研究磁流变等柔体抛光条件下去除速度均匀性与谷粒形貌的内在关系，提出改性层深度设计算法，形成谷粒形貌的有效控制方法，实现铝酸镁等红外窗口和整流罩加工表面的精准修形，达到高精度、超光滑、微亚表层损伤的加工目的，满足红外制导系统的成像要求，为红外多晶材料光学窗口和整流罩的高精度、低成本、批量生产提供理论依据和技术支持。

以红外窗口和整流罩中的理想候选材料铝酸镁为例，研究多晶材料在抛光过程中的谷粒形貌生成及抑制方法，实现高精度加工目标。对抛光颗粒尺寸、硬度、抛光盘柔度等工具参数对谷粒形貌的影响进行了分析，得到了谷粒形貌的形成机理，发现抛光工具柔性越大，谷粒特征尺寸的范围和幅值越大；去除函数束径越大，抛光效率越高，对局域误差的修形能力减弱，但对谷粒形貌的影响较小；抛光工具与红外多晶材料之间的作用力越大，谷粒特征越不明显，表层材料的去除速度更为均匀。在此基础上，提出强流脉冲电子束表面改性方法，分析了电子束能量密度、改性电压、改性时间对改性层深度和均匀性的影响规律，建立了改性层的影响模型，发现直接进行电子束改性时，铝酸镁材料的轴向温度梯度很大，热影响区与基体之间的热应力可能导致破裂现象；通过提高红外多晶材料的初始温度、降低热流密度、延长电子束轰击时间，可以大幅降低不同区域的热应力差值。为了得到电子束改性参数的合理取值范围，对加速电压、能量密度、靶源距离、轰击次数等敏感参数进行了正交试验设计，优化参数后实现了铝酸镁材料表层区域在设定深度范围内的均匀改性。研究磁流变抛光条件下去除速度均匀性与谷粒形貌的内在关系，提出改性层深度设计算法，对磁流变抛光参数进行优化，采用优化后的工艺参数抛光，改性层的峰值去除效率提高约4倍，表面粗糙度由改性前的Ra 13.28nm降低到Ra 8.89nm，谷粒形貌的峰谷值由改性前的32.0nm降低到12.5nm，并对加工后的光学性能进行了初步测试分析，表明材料加工后达到了红外光学零件的使用要求。项目的研究工作验证了电子束改性方法对于红外多晶材料表面超精密加工的可行性，为红外多晶材料光学窗口和整流罩的高精度、低成本、批量生产提供理论依据和技术支持。