Effect of Bimodal Grain Size Distribution on the Strain Hardening Behavior of a Medium-Entropy Alloy

Abstract

The evolution of strain hardening behavior of the Fe 50 (CoCrMnNi) 50 medium-entropy alloy as a function of the fraction of recrystallized microstructure and the grain size was studied using the Hollomon and Ludwigson equations. The specimens under study were partially recrystallized, fully recrystallized with ultrafine-grained microstructure, and fully recrystallized with coarse grains. The yield strength decreases steadily as the fraction of recrystallized microstructure and grain size increases due to the recovery process and the Hall-Petch effect. Interestingly, the bimodal grain distribution was found to have a significant impact on strain hardening during plastic deformation. For instance, the highest ultimate tensile strength was exhibited by a 0.97 μm specimen, which was observed to contain a bimodal grain distribution. Furthermore, using the Ludwigson equation, the effect of the bimodal grain distribution was established from the behavior of K 2 and n 1 curves. These curves tend to show very high values in the specimens with a bimodal grain distribution compared to those that show a homogenous grain distribution. Additionally, the bimodal grain distribution contributes to the extensive Lüders strain observed in the 0.97 μm specimen, which induces a significant deviation of the Hollomon equation at lower strains.

Investigation of Microstructures and Tensile Properties of 316L Stainless Steel Fabricated via Laser Powder Bed Fusion

“…However, by refining their grain sizes, their mechanical properties can be enhanced. Traditionally, grain refinement is achieved through severe plastic deformation processes, such as cold rolling, equal channel angular pressing, or dynamic plastic deformation at high strain rates [7,8], or other methods, such as the introduction of bimodal grain sizes [9] and recrystallization [10]. Fabricating complex components with these methods can be quite challenging, as extensive machining and tooling processes are needed.…”