  During Precision Glass Molding (PGM), the molding tools have to withstand
severe thermo-chemical and thermo-mechanical loads cyclically. To protect their
high-quality optical surface against degradation and increase their service
lifetime, protective coatings are applied on the molding tools. In this work,
we designed four different PtIr protective coating systems, where the thickness
of the PtIr layer and the adhesion layer were varied. Their lifetimes were
evaluated and compared using an in-house built testing bench. Among all the
studied coating systems, the protective coating, which consists of a 600nm
thick PtIr layer and a 20nm thick Cr adhesion layer, showed the best durability
with the longest lifetime. To understand the degradation mechanism of the
coating during actual engineering production, an industrial PGM machine was
used and emulation PGM tests were conducted. Detailed sample characterization
was performed using an array of complementary techniques including white light
interferometry (WLI), scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM) and
atom probe tomography (APT). Phenomena such as interdiffusion, oxidation,
coating spallation and glass sticking on the coating were observed and are
discussed in the context of optimization of the coating's performance and
durability.
