光学玻璃超精密加工表层损伤的表征方法和测试技术

In order to meet the application demands of less or no damage layer on optical elements used in modern optical system, characterization and testing of damage layer induced by ultra-precision machining should be developed to evaluate the quality of the machined surface. Aiming at the shortage of evaluating surface machining quality only by geometric dimension, nanoindentation and nanoscratch tests become promising technique for characterizing the surface damage layer because of its high testing resolution and the equivalent detection scale to the depth of the damaged layer. The critical issues of this proposed project is to detect geometric dimension of surface damage layer and test the mechanical property of the surface damage layer induced by machining process and chemical polishing. The main contents of this proposed project include: (1) Establishing an efficient method to detect the geometric dimension of surface damage layer through acquiring its microstructure; (2) Developing the mechanical testing technique for surface damage layer from brittle processing by revealing the relationship between mechanical properties and crack damage of damage layer; (3) Developing the mechanical testing technique for surface damage layer from ductile processing by considering the effect of elastoplastic deformation on mechanical properties of the damage layer; (4) Developing the mechanical testing technique for surface damage layer from chemical polishing through studying the effect of polishing parameters on mechanical properties of hydrolysis layer. This proposed project is aimed to characterize the surface damage layer of optical glass using mechanical properties for improving the evaluation system of surface processing quality and providing general reference for optimizing ultra-precision machining processes.

为满足现代光学系统对所用光学零件少无损伤表面的应用要求，须发展光学玻璃超精密加工表层损伤的表征方法和测试技术，以便评估表面加工质量。针对目前仅以几何指标评价表面加工质量的不足，纳米压入和划入技术因位移分辨力高且测试尺度与损伤层深度相当，有望成为表层损伤的力学评价手段。关键在于：建立表层损伤几何指标的检测方法；发展机械加工和化学抛光表层损伤的力学测试技术。本申请项目的主要内容包括：研究表层损伤的微观结构，建立几何指标的高效检测方法；研究裂纹损伤对表层力学性能的影响，发展脆性加工表层损伤的力学测试技术；研究弹塑性变形对表层力学性能的影响，发展延性加工表层损伤的力学测试技术；研究化学抛光加工参数对水解层力学性能的影响，发展抛光水解层的力学测试技术。本申请项目旨在发展光学玻璃表层损伤的力学表征方法和测试技术，完善表面加工质量评价体系，为优化超精密加工工艺提供通用的参考依据。

光学玻璃具有稳定的物理化学性能和优异的光学均匀性，广泛应用于航空航天和高能激光系统等领域。然而，此类材料呈脆性，在磨粒加工过程中易产生表层损伤。损伤层将显著降低光学玻璃元件的应用性能，需要采用少/无损伤抛光工艺将其去除。本项目通过发展光学玻璃损伤层几何特征和力学性能的检测技术，完善表面加工质量评价指标体系和方法，为优化超精密抛光工艺提供参考依据。主要研究内容和成果如下。. (1)发展研磨裂纹深度的化学蚀刻检测方法。通过研究磨粒加工试样表面的化学蚀刻特征，建立了以蚀刻表面PV粗糙度表征亚表面裂纹深度的测量条件，进而结合化学蚀刻方法和激光共聚焦显微镜，发展光学玻璃亚表面裂纹深度的检测方法。针对2种光学玻璃的研磨试样，采用截面抛光法获得的结果与新发展方法测量结果的偏差分别为2.56%和5.74%，两者一致性较好，表明新发展的方法基本满足测量要求。. (2)建立研磨加工表层损伤的纳米压入力学表征方法。采用角度抛光法和纳米压入方法，分别检测损伤层内裂纹和力学性能分布，研究力学性能衰减梯度与裂纹密度分布的定量关系。结果表明，裂纹密度和力学性能沿深度均以指数形式变化；损伤层内硬度衰减分布与亚表面损伤分布相似，亚表面裂纹分布成为一种表征损伤层硬度梯度的潜在指标。此方法的优势和意义在于，一次检测即可获得损伤层的几何指标和力学指标，完善精密加工的表面质量评价体系。. (3)发展磨削表层损伤的力学表征方法。首先，基于纳米压入技术从斜剖面压入粗磨加工损伤层，评估表层损伤对力学性能的影响。实验结果表明，由于粗磨加工试样测试表面的粗糙度过大，纳米压入技术难以分辨损伤层的力学性能衰减梯度；然后，基于纳米压入技术从表面压入精磨和抛光试样，实验结果发现，磨削表面的压入硬度沿深度方向增大，且硬度稳定时的深度(1.5μm)与截面抛光法测得深度(1.6μm)接近，验证了压入方式表征光学玻璃小尺度表层损伤的可行性。