Study on the Thermal Repair Mechanism for the Ultra-precision Polished Surface of Sapphire

doi:10.3901/JME.2023.15.333

Abstract

Abstract: The ultra-precision surface of sapphire machined by chemico-mechanical polishing has a certain thickness of damage layer, which has adverse effects on the performance of sapphire parts. For reducing the damage of sapphire surface, the thermal repair process is studied on the ultra-precision surface of sapphire. The high-temperature annealing treatment are conducted on the sapphire materials after ultra-precision processing. The micro-topography of sapphire surfaces is analyzed before and after thermal treatment. Based on the atomic arrangement rule of various crystalline orientations of sapphire, it reveals that the ultra-precision polished surface of C-plane sapphire is easiest to form the step structure as the interplanar spacing of C-plane of sapphire is largest among the four crystalline orientations. After annealing at high temperature, the surfaces of A- and R-planes sapphire also exhibit ordered step-like structures, and the surface of M-plane sapphire shows a lamellar structure. Under the action of thermal field, the atoms in sapphire surface move leading to the formation of step-structures. The nanoindentation results show that all the nano-hardness and elasticity modulus of sapphire with various crystalline-faces are increased to a certain extent after thermal repair. The nanoscale-thickness materials of R-plane sapphire before and after thermal repair are extracted by the cutting technology of focusing ion beam. The high-resolution atomic diffraction images are observed under transmission microscope. It is verified that the surface atomic arrangement changes from the amorphous to the ordered structures due to high-temperature repair process. At the same time, the surface morphology also tends to be ordered and regular. The ordered lattice arrangements improve the lattice integrity of the processed surface of sapphire. The research highlights that thermal repair is an effective method to the improve the surface-layer quality of sapphire.

Key words: sapphire, ultra-precision surface, annealing, repair, step structure, ordering

CLC Number:

TG156

WANG Yinhui, LIANG Zhiqiang, ZHAO Wenxiang, ZHOU Tianfeng, ZHOU Hai, WANG Xibin, ZHAO Bin. Study on the Thermal Repair Mechanism for the Ultra-precision Polished Surface of Sapphire[J]. Journal of Mechanical Engineering, 2023, 59(15): 333-340.

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