On the Portevin-Le Chatelier Effect Due to Snoek Strain Aging in the Niobium Oxygen System

Natural-mixing guided design of refractory high-entropy alloys with as-cast tensile ductility

Metallic alloys containing multiple principal alloying elements have created a growing interest in exploring the property limits of metals and understanding the underlying physical mechanisms. Refractory high-entropy alloys have drawn particular attention due to their high melting points and excellent softening resistance, which are the two key requirements for high-temperature applications. Their compositional space is immense even after considering cost and recyclability restrictions, providing abundant design opportunities. However, refractory high-entropy alloys often exhibit apparent brittleness and oxidation susceptibility, which remain important challenges for their processing and application. Here, utilizing natural-mixing characteristics among refractory elements, we designed a Ti₃₈V₁₅Nb₂₃Hf₂₄ refractory high-entropy alloy that exhibits >20% tensile ductility in the as-cast state, and physicochemical stability at high temperatures. Exploring the underlying deformation mechanisms across multiple length scales, we observe that a rare β'-phase plays an intriguing role in the mechanical response of this alloy. These results reveal the effectiveness of natural-mixing tendencies in expediting high-entropy alloy discovery.

Simulating the mechanisms of serrated flow in interstitial alloys with atomic resolution over diffusive timescales

The Portevin-Le Chatelier (PLC) effect is a phenomenon by which plastic slip in metallic materials becomes unstable, resulting in jerky flow and the onset of inhomogeneous deformation. The PLC effect is thought to be fundamentally caused by the dynamic interplay between dislocations and solute atoms. However, this interplay is almost always inaccessible experimentally due to the extremely fine length and time scales over which it occurs. In this paper, simulations of jerky flow in W-O interstitial solid solutions reveal three dynamic regimes emerging from the simulated strain rate-temperature space: one resembling standard solid solution strengthening, another one mimicking solute cloud formation, and a third one where dislocation/solute coevolution leads to jerky flow as a precursor of dynamic strain aging. The simulations are carried out in a stochastic framework that naturally captures rare events in a rigorous manner, providing atomistic resolution over diffusive time scales using no adjustable parameters.

Understanding the plastic deformation mechanism within specific ranges of temperature and strain in metal alloys is of great technological importance. Here the authors report on dynamic simulations of dislocation–solute coevolution in tungsten crystals containing a few atomic parts per million of interstitial oxygen and their relation to unstable plastic flow.