Achieving exceptionally high strength in binary Mg-13Gd alloy by strong texture and substantial precipitates

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

As the forging counterpart of fusion-based additive processes, additive friction stir deposition offers a solid-state deformation processing route to metal additive manufacturing, in which every vo...

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2020.1847211

Additive friction stir deposition: a deformation processing route to metal additive manufacturing

Revealing the tensile anisotropy, tension–compression asymmetry, and strain-hardening behavior of a high-performance Mg–Gd–Ag alloy

A high-strength binary Mg–15Gd alloy plate, prepared by the conventional extrusion, warm-rolling and aging, exhibits an excellent mechanical property with 504, 518 MPa and 4.5% for yield strength, ultimate tensile strength and elongation, which is mainly attributed to the nano substructure with boundary segregation of Gd atoms, the high-density nano clusters induced by dislocations in the interior of grains, the high-density dynamical precipitates with submicron size, and the strong basal texture. GRAPHICAL ABSTRACT IMPACT STATEMENT A new strengthening mechanism involving the nano substructure with Gd segregation, high-density nano Gd clusters induced by dislocations, and high-density dynamical precipitates has been found in Mg–Gd binary alloys.

Achieving a high-strength binary Mg–15Gd alloy by nano substructure with Gd segregation and nano clusters1

The opportunities for wrought magnesium products in a wide range of structural and functional materials for transportation, energy generation, energy storage and propulsion are increasing due to th...

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2020.1719227

R. C. Brennan

Papers

Achieving extraordinary structural efficiency in a wrought magnesium rare earth alloy