Tailoring grain growth and solid solution strengthening of single-phase CrCoNi medium-entropy alloys by solute selection

The CoCrFeMnNi alloy is one of the most notable first-generation high-entropy alloys and is also known as a Cantor alloy. This alloy was first proposed in 2004 and shows promising performance at cryogenic temperatures (CTs). Subsequent research has indicated that the equiatomic ternary CoCrNi medium-entropy alloy (MEA), as a subset of the Cantor alloy family, has better mechanical properties than the CoCrFeMnNi alloy. Interestingly, both the strength and ductility of the CoCrNi MEA are higher at CTs than at room temperature. CoCrNi-based alloys have attracted considerable attention in the metallic materials community and it is therefore important to generalize and summarize the latest progress in CoCrNi-based MEA research. The present review initially briefly introduces the discovery of the CoCrNi MEA. Subsequently, its tensile response and deformation mechanisms are summarized. In particular, the effects of parameters, such as critical resolved shear stress, stacking fault energy and short-range ordering, on the deformation behavior are discussed in detail. The methods for strengthening the CoCrNi MEA are then reviewed and divided into two categories, namely, modifying microstructures and adjusting chemical compositions. In addition, the mechanical performance of CoCrNi-based MEAs, including their dynamic shear properties, creep behavior and fracture toughness, is also deliberated. Finally, the development prospects of CoCrNi-based MEAs are proposed.

A critical review of the mechanical properties of CoCrNi-based medium-entropy alloys

Microstructure and texture of CoCrNi medium entropy alloy (MEA) processed by severe cryo-rolling: A study vis-a-vis cold-rolling

An attempt was made to illustrate the effects of microstructure, texture, and properties in heavy cold- and warm-rolled equiatomic CoCrNi MEAs during deformation and subsequent annealing. The MEA was cold-rolled (CR) at ambient temperature and warm-rolled at 400 (WR(400)) and 600 °C (WR(600)) to reduce the thickness by 90%. The rolled alloys were further annealed at temperatures ranging from 700 to 1200 °C. The CR- and WR(400)-processed materials showed fine lamellar structures. In contrast, the WR(600) material showed an equiaxed microstructure. The CR material showed a brass ({112} )-dominated texture, corroborating the low stacking fault energy (SFE) of the MEA. In contrast, the WR(400) specimen showed a prominent α-fiber (ND// ) but a noticeably weakened brass component. The WR(600) material also showed the presence of α-fibers due to recrystallization. The recrystallized CR and WR(400) materials showed decidedly larger grain sizes than the WR(600) material due to the differences in the grain boundary character distribution. The recrystallization textures showed α-fiber components, thus elucidating that the deformation texture components are preserved, as preferential nucleation, and preferential growth were not significant factors. The WR(400)-processed annealed specimen showed a significantly improved yield strength (~ 1120 MPa)-ductility (elongation ~ 19%) balance, establishing warm rolling as an attractive processing route.

Influences of Thermomechanical Processing by Severe Cold and Warm Rolling on the Microstructure, Texture, and Mechanical Properties of an Equiatomic CoCrNi Medium-Entropy Alloy

Preparation of high-mechanical-property medium-entropy CrCoNi alloy by asymmetric cryorolling

An equiatomic CrCoNi medium-entropy alloy plate was heavily deformed by conventional cold rolling and subsequently annealed at different temperatures. Microstructure and texture evolution of the deformed and annealed sheets were investigated by electron backscatter diffraction and X-ray diffraction. Heavy cold rolling induces an alloy type α-fibre texture with major brass component. This type of texture is indicative of low stacking fault energy of the CrCoNi alloy. Annealing at 700 °C leads to a homogeneously recrystallized microstructure with ultrafine grains of about 800 nm average size. The volume fraction of different texture components is almost similar after annealing at different temperatures. However, the overall texture intensity after annealing is very weak. Finally, in order to understand the microstructure and texture evolution of the CrCoNi alloy, it is critically compared with other low stacking fault energy FCC materials.

Gunasekaran Dan Sathiaraj

Papers

Microstructure and Texture of Cold Rolled and Recrystallized CrNoNi Medium-Entropy Alloy

Microstructure, mechanical properties, and strain rate sensitivity of vacuum arc melted CoCrNi medium entropy alloy