Effect of constrained inter-granular regions on the inverse Hall-petch phenomena

The paper makes an effort to lay out a critical assessment of grain size and its role in limiting strength gains in stable nanocrystalline (NC) metals. In particular, this study uses copper-tantalum binary alloys, in which the predominate mechanisms of grain boundary sliding and rotation are shut down, to decipher the breakdown of classical Hall-Petch behavior and its underlining mechanisms. Through varying grain sizes and tantalum concentrations, the results show Cu–Ta's strength exceeds the traditional strength limits anticipated when strictly applying smaller grain size translates to greater strength than that from the Hall-Petch relationship for NC Cu. Within this work, we also highlight the consistent linear behavior holding up to the point of losing full crystallinity given this alloy's ability to constrain failures occurring within other non-stabilized NC systems.