Mechanistic investigation of the interface crystallization behavior of amorphous-Co bonding phase under thermal conditions and its impact on cohesive strength via new phase precipitation

Abstract

This study employed molecular dynamics (MD) simulations combined with X-ray diffraction (XRD) and scratch testing to explore the interface crystallization behavior of amorphous-Co under thermal conditions and the impact of new phase precipitation on the cohesive strength of WC/Co coatings. Microstructural analysis revealed the phase transformation induced by heat treatment, as amorphous-Co gradually transformed into the η-phase, with the transition starting at 873 K and completed at 1173 K. The results of the scratch testing indicated that appropriate heat treatment could enhance the coating's cohesive strength and thereby improve its performance under certain conditions. Nonetheless, at 873 K, the early stage of η-phase nucleation exhibited elastic strain, leading to an abnormal decrease in the coating's cohesive strength. MD simulation results demonstrated that the crystallization of amorphous-Co primarily occurred at the WC/Co interface, and the ideal fracture energy (W_sep) increased with increasing heat-treatment temperature. However, after heat treatment at 873 K, the W_sep between the atomic layers within amorphous-Co slightly decreased and was reflected as a decrease in the coating's cohesive strength at the macroscopic level.