Basic study on Ultraprecision machining of Single-crystal Calcium Fluoride

Calcium fluoride (CaF2) has a wide range of change of refractive index and permeability of wavelength from vacuum ultraviolet range to infrared range so that it is utilized for lenses or prisms. CaF2 has been fabricated using conventionally grinding and polishing combined with interferometry and local surface correction to form the desired flat, sphere or aspherical surface. In this study, the mechanical properties and crack initiation on the (100), (110) and (111) planes of CaF2 are examined by nanoindentation and micro-Vickers hardness tests. In addition, brittle-ductile transition is investigated by performing an orthogonal cutting test with ultraprecision machine tool. The results of these tests show that the critical depth of cut remarkably changes on the basis of the crystal orientation on each plane. We have discussed these changes from the viewpoint of slip system and cleavage.