Microstructural changes of amorphous Mo–B–C coatings upon thermal annealing

Several amorphous Mo–B–C coatings with wide range of compositions were subjected to thermal annealing to a final temperature of 1000 °C in UHV conditions. The nature of the induced recrystallization depended mostly on the Mo content in the coating. A higher Mo content resulted in a nanocrystalline Mo2C phase, a lower Mo content in a nanocrystalline Mo2BC phase and Mo content in-between resulted only in a near-amorphous microstructure. In all cases, the hardness and effective elastic modulus increased significantly after annealing up to values of ∼29 GPa and 500 GPa, respectively. The cobalt diffusion from the WC-Co substrates affected the lower parts of coatings forming a MoCoB interface.