Deformation behavior of hard ceramic layer coated Ti composite: <i>in situ</i> characterization and molecular dynamics simulation

A multilayer hard ceramic layer coated Ti composite was prepared through plasma electrolytic oxidation (PEO) combined with microwave hydrothermal (MH) treatment. After PEO and PEO-MH treatment, the in-situ formed ceramic coating significantly affected the deformation behavior of the Ti matrix, and the deformed slip bands appeared at a greater deformation on the Ti matrix during the tensile process; the deformation texture was also observed. Additionally, compared to pure Ti, the tensile strength, yield strength and elongation of the PEO and PEO-MH exhibited slight increases. The presence of the hard ceramic layer effectively inhibited crack propagation at the substrate/coating interface. Moreover, the self-interlocking effect at the coating/substrate interface generated by the corrosion grooves further optimized the stress distribution at the coating/substrate interface, and the ratio of amorphous to crystalline phases also played a crucial role in adjusting the deformation behavior of the Ti matrix. After MH treatment, the PEO-MH possessed more titania nanocrystalline clusters and a multilayer structure, promoting more uniform deformation of the Ti composite. Notably, an intriguing crystalline-to-amorphous phase transformation process was observed through in situ tensile tests and molecular dynamics simulation. This phase change, which occurs at the crack tip, effectively alleviates the stress concentration phenomenon, resulting in lattice distortion that ultimately enhances the strength of the Ti composite. This research provides crucial insights into the application of Ti composite in high-load environments and establishes a solid foundation for their broader utilization in the future.