Numerical and experimental investigation on thermal shock failure of Y2O3-coated CVD ZnS infrared windows

Infrared transparent windows on aircraft and missiles can be subjected to extreme aerothermodynamics, which can cause thermal shock failure. Finite element analysis and oxygen-propane flame jet impingement tests were performed to investigate the thermal shock failure of an yttrium oxide-coated chemical vapor deposition (CVD) ZnS infrared window. Good agreement was achieved between the simulation and experimental results, which indicated that thermal shock failure occurs under high temperature differences and thermal stresses. The temperature and stress in the samples increased rapidly in a few seconds and then trended to be stable. The center area of the window surface failed most easily because the maximum temperature and stress both occurred in this area. No delamination of the Y2O3 films occurred during the thermal shock, which indicated good adhesion between the Y2O3 films and CVD ZnS substrate. In the experiment, the center area of the specimen surface was damaged in the form of pits and line cracks.