Pressure Annealing Study for Reducing Residual Stress of m-CVDZnS Products
ZHOU Jieming1, LI Jianming2, LI Dongxu2, ZHAO Yongtian2, YANG Hai1,2, WEI Naiguang1,2
1 Beijing General Research Institute of Nonferrous Metals, Beijing 100088, China 2 Beijing General Research Institute of Nonferrous Metals Guojing Advanced Materials Co., Ltd., Sanhe 065201, Hebei, China
Abstract: Zinc sulfide (ZnS) has high infrared transmittance and good mechanical, thermal and optical properties. The multi-spectral zinc sulfide (m-CVDZnS) has a wider transmission range (0.35—13 μm) after hot isostatic pressing, meeting the needs of composite guidance, and is the key material for the infrared dual-band aircraft observation windows and domes. The residual stress in the m-CVDZnS polycrystal directly affects the optical uniformity of the windows and domes and the optical imaging quality. In this work, the in-situ annealing of CVDZnS poly-crystalline samples in the hot isostatic pressing equipment is carried out. After the protective Ar gas reaches the pressure required by the hot isostatic pressing at a constant high temperature, the annealing process is no longer carried out for pressure charging or pressure relief, ie. stress annealing. The annealing samples are a number of m-CVDZnS polycrystalline polished samples with a size of about 120 mm×165 mm×10.2 mm. The optimized process of typical pressure annealing is as follows: high temperature annealing conditions using 990 ℃/150 MPa, combined with 600 ℃ constant temperature annealing and slow cooling annealing, Ar gas used as shielding gas during the whole annealing treatment. The results of sample annealing stress birefringence measurement show that the residual stress after the annealing treatment decreases significantly with the average value of stress birefringence reduced from 12—13 nm/cm to 3—5 nm/cm, which is approximately 100% reduction. The uniformity of stress distribution after annealing treatment is improved markedly.
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