Fracture mechanism of TiN coatings on Ti-6Al-4V substrates: Role of interfaces and of the residual stress depth profile

• Published in: Surface & coatings technology 2021-11, Vol.426, p.127747, Article 127747
• Main Authors: Herrera-Jimenez, E.J., Vanderesse, N., Bousser, E., Schmitt, T., Bocher, P., Martinu, L., Klemberg-Sapieha, J.E.
• Format: Article
• Language: English
• Subjects: Argon plasma; Coatings; Compressive strength; Crack propagation; Crystal defects; Energy release rate; Failure mechanism; Failure mechanisms; Fracture mechanics; Fracture toughness; Hardness; Interfaces; Interfacial shear strength; Interfacial shear strength and critical energy release rate; Mechanical properties; Micro-scratch test; Micro-tensile testing; Modulus of elasticity; Plasma processing; Residual stress; Shear strength; Stress propagation; Substrates; Surface and interface engineering; Surface cracks; Surface layers; Tensile tests; Titanium base alloys; Titanium nitride; X ray reflection
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.127747

The performance and integrity of coated engineering components rely on the time required for the appearance of defects and cracks and their propagation, leading to delamination of the coating and degradation of the substrate. Optimizing the coating's mechanical properties such as hardness, residual stress (RS), and adhesion is essential to delay crack onset and propagation. In the present work, we investigate the mechanical properties, and the failure mechanisms of model TiN coatings reactively sputtered onto Ti-6Al-4V substrates while comparing three interface engineering approaches to enhance the system durability: a) Argon plasma treatment, b) plasma surface nitriding, and c) Titanium implantation. The TiN coatings possessed a hardness of ~29 GPa and a Young's modulus of ~350 GPa. Multi-reflection grazing incidence X-ray diffraction was used to assess the compressive RS depth profile. Each interface engineering process induced RS variation in the coating and the adjacent interfacial area and in the substrate's near-surface layer ranging from −1 GPa to −2.2 GPa with different gradients. Cohesive failure, crack evolution and fracture toughness were studied using micro-scratch and micro-tensile tests, while the surface grain deformation behaviour and surface cracks on fractured Ti-6Al-4V with various interface treatments and TiN coatings were identified by SEM image and elasto-plastic property analyses. We found a close correlation between the RS of the coatings or the interface layers and the fracture mechanism. Specifically, higher compressive RS led to an enhanced interfacial shear strength and a critical energy release rate of around 550 to 790 MPa, and of ~18 J/m2, respectively. •Residual stress gradient is correlated to the fracture mechanism of coated samples.•Interface plasma treatments of Ti6Al4V influence surface deformation and cracks.•Compressive residual stress levels delay component failure and enhance durability.•Interfaces with compressive stress reduce the elastic-plastic deformation of Ti6Al4V.•Enhancement of coating-substrate elastic coupling improves interfacial shear strength.