Mechanical behavior of high-entropy alloys

Most multicomponent high-entropy alloys (HEAs) lose ductility with increasing strength, similar to conventional materials. We controllably introduced novel gradient nano-scaled dislocation-cell str...

Gradient-cell–structured high-entropy alloy with exceptional strength and ductility

A review of hot deformation behavior and constitutive models to predict flow stress of high-entropy alloys

Effects of NbC content on microstructural evolution and mechanical properties of laser cladded Fe50Mn30Co10Cr10-xNbC composite coatings

The paradigm shift of alloying approach that led to high entropy alloys (HEAs) is now well established. Although the initial years were dominated by equiatomic approach, recent years have seen expansion in non-equiatomic compositional space that can be termed as complex concentrated alloys (CCAs). These HEAs/CCAs provide opportunities for tunable performance by manipulating deformation mechanisms. Understanding has advanced to the point that certain aspects of core effects (entropy of mixing, lattice distortion, sluggish diffusion, and cocktail effect) can be critically examined. In addition, new aspects of metastability engineering and emergence of a wide range of processing strategies has put this field on an exponential growth path. In this review, we categorize the compositional and microstructural approaches that exhibit potential for a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms. The emerging HEAs give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), which have guided design of next-generation steels over the last 20 years to a new level. For TRIP HEAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. On the other hand, hierarchical microstructural engineering in AlxCoCrFeNi alloys can lead to over 2 GPa strength and >10% ductility. Observations of evolving c/a ratio in HCP phase of certain HEAs hint at possibility of new micromechanisms. While crack tip twin-bridging has been shown as a key mechanism to extend the toughness, concurrent phase transformation at the crack tip has been shown to push the fatigue endurance limit. Tunability of deformation mechanisms in HEAs is unprecedented as compared to the conventional metallic materials, particularly in compositions that exhibit shear induced transformation. The opportunities can be further enhanced by integrating the compositional and microstructure domains, and these aspects are highlighted in this review. The microstructural tailoring can take advantage of high enthalpy states in metastable HEAs with low stacking fault energy values of

High entropy alloys – Tunability of deformation mechanisms through integration of compositional and microstructural domains

High-entropy alloys with heterogeneous microstructure: Processing and mechanical properties

Deformation-induced grain boundary segregation mediated high-strain rate superplasticity in medium entropy alloy

Numerous studies have explored new materials for electrocatalysts, but it is difficult to discover materials that surpass the catalytic activity of current commercially available noble metal electrocatalysts. In contrast to conventional transition metal alloys, high-entropy alloys (HEAs) have immense potential to maximize their catalytic properties because of their high stability and compositional diversity as oxygen evolution reactions (OERs). This work presents medium-entropy alloys (MEAs) as OER electrocatalysts to simultaneously satisfy the requirement of high catalytic activity and long-term stability. The surface of MEA electrocatalyst is tailored to suit the OER via anodizing and cyclic voltammetry activation methods. Optimized electrical properties and hydrophilicity of the surface enable an extremely low overpotential of 187 mV for achieving the current density of 10 mA cm-2 alkaline media. Furthermore, a combined photovoltaic-electrochemical system with MEA electrocatalyst and a perovskite/Si tandem solar cell exhibits a solar-to-hydrogen conversion efficiency of 20.6% for an unassisted hydrogen generation system. These results present a new pathway for designing sustainable high efficiency water splitting cells. 

MIRI FREILICH

Papers

High-entropy alloys with heterogeneous microstructure: Processing and mechanical properties

High-entropy alloys with heterogeneous microstructure: Processing and mechanical properties

Deformation-induced grain boundary segregation mediated high-strain rate superplasticity in medium entropy alloy

Deformation-induced grain boundary segregation mediated high-strain rate superplasticity in medium entropy alloy

Surface‐Tailored Medium Entropy Alloys as Radically Low Overpotential Oxygen Evolution Electrocatalysts