Research On Mechanical Behavior Of Diamond Growth And Machining Process

Diamond integrates many kinds of excellent properties, which is one of the most widely used materials at present. But its high brittleness hinders the development prospects. The laser cutting process of single crystal diamond and the cooling process of polycrystalline diamond can damage the diamond itself due to its brittleness. Therefore it is very important to study the mechanical behavior of diamond growth and processing.In this paper, the mechanism of fracture mechanics and crack growth of diamond was studied. The pulse laser cutting process of CVD single diamond was studied from the viewpoint of energy. Considered the input energy of diamond system, the output energy, energy loss and energy conversion, the energy used to form crack Ecrack in brittle failure behavior could be expressed. According to the theory of fracture mechanics, the formula of crack length could be expressed as well.Secondly the fracture behavior of single crystal diamond had been studied. After pulse laser cut, laser scanning confocal microscope was used to observe the phenomenon of the coexistence of the pulse laser ablation and the fracture morphology. It is concluded that the heat distribution of the pulsed laser is not uniform, which leads to large scale defects and damage in the crystal. The phase composition of the fragments was obtained by using Raman spectroscopy; the theoretical analysis of pulse laser cutting was verified.Then, the thermal stress in the process of polycrystalline diamond growth was simulated. Four simplified assumptions were proposed to simplify the simulation. The model of membrane structure system was established by using ANSYS. The thermal stress of CVD polycrystalline diamond growth process was simulated, and the size is 0.5967~0.6406 GPa. The effects of different process parameters on thermal stress were studied: the influences of different temperature, diamond film radius, polycrystalline diamond film thickness and substrate material on the thermal stress were studied. The growth process was obtained by keeping the thermal stress in a smaller numerical value: the preparation temperature should be controlled in the range of 1150±50 K, the radius of the base should be controlled below 25.4 mm and thickness has larger impact on the stress, in the initial part of preparation the thickness needed to pay more attention to. And the base material should be chosen to get close to the thermal properties of polycrystalline diamond. But from the quantitative aspect, the effect of temperature and radius on residual stress is small, and it can be ignored.Finally, the theoretical analysis and experimental verification of the residual stress of polycrystalline diamond were carried out. Scanning electron microscopy was used to observe the microstructure of the surface, it is proved that the coefficient selection has error in the calculation formula of residual stress. The numerical value of thermal stress was 0.148 GPa calculated by Raman spectrum characteristic peak displacement. The reason of the difference between the simulation result and the simulation result is expounded:(1) Coefficient selection is not accurate;(2) The finite element model of the simplified assumptions leading to the error of the results of finite element simulation;(3) The acid can change the microstructure of polycrystalline diamond, which leads to the change of the residual stress in polycrystalline diamond film.