Enhancing thermal stability and crack resistance in Co-Cr-Ti superalloy films through Mo doping: A combinatorial study

In this study, we investigated the effects of 1.5 at.% Mo doping on the microstructure, hardness, and electrical resistivity of Co_51∼86Cr_9∼41Ti_2∼11 thin-film alloys. Two batches of thin films were deposited, one at room temperature and the other at 600 °C, followed by annealing at 650 °C for 4 h to evaluate property changes after heat treatment. Without Mo doping, only lower Co content (less than ∼70 %) alloys exhibited significantly reduced annealing-induced cracking in both batches. With Mo doping, crack formation was found to be reduced or suppressed across all deposition conditions and compositions. Moreover, for room-temperature-deposited thin-film alloys with lower Co content, Mo doping facilitated the formation of an amorphous phase, which transformed into an amorphous-nanocrystalline composite upon annealing, achieving an exceptional hardness of 17.9 GPa. In films deposited at 600 °C with higher Co content (greater than ∼70 %), Mo doping stabilized nanolamellar structured precipitates, which helped mitigate thermal stress concentration by distributing it throughout the alloy matrix and eliminating observable cracks. These findings highlight the dual role of Mo in enhancing the mechanical properties and thermal stability of Co-Cr-Ti thin-film alloys, offering valuable insights for the design of high-performance superalloys.