Study On Ultra-precision Machining Assisted With Ion Implantation

Hard and brittle materials are widely utilized in many areas due to the physical and chemical properties. Although an optical surface could be achieved using ultra-precision machining, the machining results would ultimately suffer from the hard and brittle nature of those materials. The brittle-ductile transition(BDT) is the key process affecting the mode of material removing and the hot spot in ultra-precision machining and material science all the time. To solve the problems mentioned above, a new ultra-precision machining method, which is assisted by surface modification through ion implantation(Ni IM), has been proposed by our team. Lattice damages or amorphization is previously introduced by an ion beam to reduce the hardness and elastic modulus of the surface layer. As a result, the tool life is prolonged with the guarantee of ductile region machining. The validity of this method has been proofed preliminarily on silicon, silicon carbide, etc. Meanwhile, as a newborn method, Ni IM needs to be studied systematically to refine its theoretical content. In this thesis, the essentials of ultra-precision machining are reviewed, including mainstream theories, experimental results, the restraints of computer calculation and the research status of Ni IM. The main research work is as follows:1. The empirical results of BDT are obtained at micro-scale based on the discussion of molecular dynamics and characterization of cutting region. Then the influence rules of processing parameters are analysed. Compared with ductile material, the understanding of hard and brittle material nanometric cutting has been deepened.2. Further researches on the mechanism of Ni IM are conducted to explore the relations between processability and implantation and cutting conditions of the workpiece. In addition, the method of process parameter design has been proposed with the assistance of Monte Carlo calculation and some optimization schemes for freeform turning are briefly described.3. Ion implantation is performed on monocrystalline germanium. The brittle-ductile transition depth is enhanced significantly in the cutting test, which confirms the theoretical analysis results. What's more, it is found that the cutting performances are different between nomal and modified workpiece and preliminary interpretation is attached.