Mineral bridge thermal toughening of composite DLC coating to improve the mold thermal stability at 500 °C high temperature

The extensive application of diamond-like carbon (DLC)-coated molds in glass molding processes has been constrained by thermal expansion mismatch between the mold substrate and coating. Critical challenges involve maintaining DLC layer integrity under elevated temperatures and enhancing the service temperature limits of DLC-coated molds. This study proposes a mineral bridge thermal toughening (MBTT) method to improve the mechanical performance of coatings, thereby increasing the service temperature of DLC-coated molds. A titanium transition layer was implemented to mitigate thermal expansion discrepancies between the DLC layer and mold substrate via amorphous phase reaction with nickel in the substrate. High-temperature stepwise heat treatment facilitated interface diffusion reactions between nickel and titanium, inducing the formation of nickel crystalline mineral bridges. The mechanisms governing coating fragmentation and mineral bridge formation were elucidated, accompanied by a shear lag model to optimize transition layer thickness, mineral bridge density, and service temperature. A 70 nm transition layer optimally balances thermal stability and mechanical performance, enabling sustained operation at 500 °C while maintaining maximum internal stress below the DLC layer's yield strength. A mineral bridge density of 10 bridges per micron length minimizes transitional layer stress. Surface profile errors caused by mineral bridge formation negligibly affect mold service performance. This work establishes a practical methodology for enhancing the high-temperature performance of DLC-coated molds.