| Single crystal MgO has good thermal stability, light transmittance, electrical insulativity, chemical stability and mechanical properties. It is mainly used as substrate for high temperature superconductor (HTS) thin films and also a kind of important optical material. The surface quality of the ultra-precision machined substrates greatly affects the performance of the thin films grown on it. However, the micromechanical characteristics, the damage mechanism and the precision processing technology of MgO substrates have not been systematically studied, the applications of single crystal MgO have been limited. In this dissertation, the nano-mechanical behhavior, microscopic deformation and surface layer damage mechanism of single crystal MgO were studied, and abrasive processing technology were investigated. It has great theoretical significance and applied value to promot the application of single crystal MgO in the optoelectrionics field.The main research contents and conclusions are as follows:The nano-mechanical properties, microscopic deformation and surface layer damage characteristic were investigated by nanoindentation, micro-indentation and micro-scratch on different crystallographic planes of single crystal MgO. Under different loading conditions, single crystal MgO present different deformation, including elastic deformation, plastoelastic deformation, creep deformation, micro cracks and micro fractures. The load-displacement curve of elastic deformation fits well with the curve of Herz elastic contact, the elastic deformation can recovery after unloading. The plastic deformation is the result of the dislocations nucleation and glidding in the {110} easy slip planes of MgO. There is pop-in phenomenon on load-displacement curve of nanoindentation at the transition point from elastic to plastoelastic deformation, which is associated with the acoustic emission (AE) signal with distinct waveform, and the elastic released energy of pop-in is in proportion to AE energy. The average critical shear stress of dislocation nucleation of nanoindentation on MgO (001) and MgO (110) planes were calculated to be 14.85 GPa and 12.61 GPa, which are very close to the theory critical shear stress of 13.82 GPa. Increasing the holding time in nanoindentation induces creep deformation, including transient stage creep and steady stage creep. The creep stress exponents of MgO (001), (110) and (111) planes in steady state creep were calculated to be 36.5,53.7 and 22.4, respectively. When increasing the load of micro-indentation and micro-scratch to a certain extent, micro cracks including radial cracks, lateral cracks and median cracks generate in surface and subsurface of MgO. Through the cross-section observation of the micro-indentation and micro-scratch on MgO, two types of subsurface cracks were confirmed according to the different forming mechanism. One is the cracks in (110) planes, including the {110}90°cracks and inclined cracks, intersecting the top (001) surface at 90°and 45°, respectively, which result from the intersection and blocking of dislocations gliding in two easy slip planes intersecting each other at 120°; the other is the median cracks (vertical to the top (001) surface) or lateral cracks (parriable to the top (001) surface), which result from the cleavage in the (100) easy cleavage planes.Based on the analysis of micromechanical behavior, the surface and subsurface damage of MgO substrates were studied through the observation of the surface and cross-section of sawed, lapped and ground MgO substrates. The vertical apnd inclined dislocation glidding systems were observed in the cross-section of MgO substrates machined by different abrasive processing methods. The vertical slip lines come from the dislocations glidding in the {110}90°easy slip planes, and the inclined slip lines result from the dislocation glidding in the {110}45°slip planes. Three basic shape cracks including lateral cracks, vertical cracks and inclined cracks were found in the cross-section of the rough machined MgO substrates. Other cracks with complicated shapes, such as the "hook" crack, the "zigzag" crack, the "chevron" crack and the "umbrella" crack, consist of the above mentioned three basic cracks.Based on the observation and analysis of the surface and subsurface damages of MgO substrates, the material removal mechanism of rough and fine processing MgO substrates was analyzed and the model of subsurface damage induced in MgO substrates after rough and fine processing were proposed. In rough processing MgO substrate, the material is removed in fracture mode by the extension and intersection of large numbers of median cracks, radial cracks and lateral cracks, the formed surface have micro-steps structures, and the subsurface damage layer consists of the fracture layer, the dislocation glidding layer and the elastic deformation layer.In fine processing MgO substrate, the material is removed in fatigure failure mode by the high strain result from the continuous plastic deformation and the subsurface damage layer is composed of the dislocation glidding layer and the elastic deformation layer.The systematic precision lapping experiments of MgO substrates wconducted, the influences of processing parameters on the surface roughness, material removal rate and surface damage were studied, the processing route composed of rough lapping, semi-fine lapping and fine lapping and resonable processing paramaters were obtained. Furthermore, the ultra-precision grinding technology of MgO substrates with diamond wheel was investigated. Compared with the lapping technology, the grinding has much higher machining efficiency under the condition of obtaining comparative surface quality and subsurface damage, and shows bright application prospect.
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