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Heterostructured (HS) materials have attracted extensive attention due to their superior mechanical properties. However, there are still many fundamental issues to be solved, like the microstructural evolution process of the hetero-zones during deformation. Here we reported a HS 316L stainless steel generated by exploiting the chemical heterogeneity strategy via thermomechanical processing. The plastic deformation behaviors of the hetero-zones were investigated using three-point bending tests and interrupted tensile tests characterized by electron channeling contrast imaging (ECCI) combined with electron backscattered diffraction (EBSD) techniques. These in situ observations demonstrate the evolution of hetero deformation-induced (HDI) stress field near the austenite/ferrite interfaces in terms of geometrically necessary dislocation (GND) pileups, which can modulate the plastic deformation behaviors of both austenite and ferrite phases. At the early deformation regime, the imposed plastic deformation can be well maintained by the dense and homogeneous activation of slip systems in austenite phases and the stress concentration near austenite/ferrite interfaces can be alleviated by the gradual activation of plastic deformation in the ferrite phases. At the large deformation stage, a progressive twinning-induced plasticity (TWIP) effect caused by the chemical heterogeneity can provide a stable work hardening ability in a broad strain range, which can significantly enhance the ductility. At the late stage of deformation, strain-induced α′-martensite is also triggered, which provides an additional work-hardening ability. The strategy of micro-tuning deformation mechanisms by chemical heterogeneity is versatile and can be applied to many alloys. [ABSTRACT FROM AUTHOR]

In this work, the mechanical responses of the as-recrystallized CoCrNiMo x (x = 0 to 0.2) medium entropy alloys (MEAs) across a wide range of strain rate from quasi-static (1 × 10−3 s−1) to dynamic (5 × 103 s−1) were systematically investigated. At 1 × 10−3 s−1, the slightly increased yield strength (YS, ∼133 MPa) of the Mo 0.2 alloy compared to the Mo 0 alloy is mainly due to Orowan looping of dislocations around the σ precipitates. At 5 × 103 s−1, the Mo 0.2 alloy shows a superhigh YS increment (∼880 MPa) compared to the Mo 0 alloy, and also a superhigh strain rate sensitivity of ∼0.54 in the dynamic realm. We propose that this strain-rate hardening effect is originated from the local strain rate increase near the hard σ precipitates. After dynamic straining, we evidenced vast deformation products including, the basic twin-twin intersections in the Mo 0 alloy, the HCP islands at twin boundaries in the Mo 0.1 alloy, and the close-packed nano blocks as well as the amorphous bands in the Mo 0.2 alloy. These endows the CoCrNiMo x MEA family in particular Mo 0.2 high potential to be developed for dynamic load-bearing and energy-absorbing. [ABSTRACT FROM AUTHOR]

Developing alloys with high strength and large ductility has always been a relentless pursuit. Employing hierarchical microstructures ushers in a crescendo of achieving this goal. Partial recrystallization and hierarchical precipitation are two commonly used approaches to producing hierarchical microstructures. However, employing one of them often embrittles the material and reduces work-hardening capability. Herein, we report that via coupling partial recrystallization and hierarchical precipitation, a strong and ductile medium-entropy alloy (MEA) can be successfully developed. In the model (Ni 3 CrV) 100- x Al x (x = 0, 3, 6 and 9 at.%) MEAs, increasing the Al content not only retards recrystallization due to the resultant solute drag and Zener pinning, but also promotes hierarchical precipitation through elemental partitioning, which produces hierarchical precipitates embedded in the partially recrystallized matrix with large chemical complexity. As a result, the dual-hierarchical structure endows (Ni 3 CrV) 91 Al 9 alloy with a tensile yield strength of 1151 ± 33 MPa and an ultimate tensile strength of 1448 ± 17 MPa, as well as a uniform elongation of 17% ± 1%. The complex hierarchical structure brings multiple strengthening mechanisms, i.e., hetero-deformation-induced (HDI) strengthening, precipitation strengthening and dislocation strengthening, which lead to the observed high strength. Also, such complex structure heterogeneities facilitate multiple deformation behaviors, i.e., planar slip, wavy slip, stacking faults, dislocation networks and twinning deformation at different loading stages, which give rise to the large ductility and pronounced work-hardening capability. [ABSTRACT FROM AUTHOR]