Preparation and Evaluation of Thin CVD‐ZnS‐Coated Multispectral ZnS Ceramics

Multispectral ZnS (MS‐ZnS) ceramics offer excellent infrared transparency but suffer from critically low mechanical strength (<40 MPa), limiting their application in harsh environments. To overcome this structural trade‐off, we demonstrate a practical surface‐engineering approach by applying a thin homomaterial chemical vapor deposition (CVD) ZnS coating onto one surface of the MS‐ZnS. Evaluating various coating thicknesses revealed that an optimized 20‐µm coating dramatically enhanced the mechanical performance, more than doubling the flexural strength to 110 MPa and increasing Vickers hardness to 1.6 GPa. Crucially, this reinforcement was achieved without significantly compromising multispectral clarity, maintaining an excellent optical transmittance of 71.3% at 1.064 µm. Furthermore, we identified that thicker coatings degraded visible‐range transmittance without providing additional structural gains. These findings establish the 20‐µm CVD coating as a definitive, ready‐to‐implement design baseline for highly durable infrared windows and domes.