On the theoretical foundation for the microcutting of calcium fluoride single crystals at elevated temperatures

摘要

The machining of a CaF2 lens with the near-perfect crystal structure poses a more challenging task than simply performing a ductile-regime cutting on brittle materials to achieve an optical surface finish without microcracks in the subsurface layer. This research advances the understanding of the ductile-brittle transition mechanism through material characterisation. The convincing evidence for the advantage of ultraprecision diamond turning over the optical polishing process is disclosed in the comparative experimental tests. A promising solution of thermally enhanced microcutting is proposed to meet both the ubiquitous and ad hoc requirements for the fabrication of the CaF2 lens. The theoretical foundation for the CaF2 microcutting at elevated temperatures is for the first time established based on a semi-quantitative modelling and simulation with the crystal plasticity finite element method.