Mechanical Behavior of Differently Oriented (CoCrFeNi)94Ti2Al4 Single Crystals

The paper analyzes the mechanical behavior and plastic deformation mechanisms (slip, twinning) in single-crystalline high-entropy fcc alloy (CoCrFeNi)(94)Ti2Al4 (at%) in relation to the crystal orientation ([(1) over bar 44] , [001]), type of deformation (tension, compression), and heat treatment (quenching, aging at 923 K for 4 h). The analysis shows that after aging at 923 K for 4 h, compared to quenching, the critical shear stress of such crystals increases by 20-30 MPa at 77-973 K due precipitated gamma'-phase particles of size 3-5 nm. The onset of their plastic flow, irrespective of the heat treatment, is associated with slip such that their critical shear stress depends neither on the crystal orientation nor on the type of deformation (tension, compression) at 77-973 K. When deformed at 77-973 K after quenching or aging, the [(1) over bar 44] and [001] crystals reveal a planar structure with dislocation pileups. In the quenched and aged [(1) over bar 44] crystals, twinning occurs after previous tensile slip deformation to 40% at 77 K. The stages of flow curves, the strain hardening coefficient, and the plasticity of the crystals are found to depend on their orientation, test temperature, and heat treatment. The dependences of the strain hardening coefficient of the crystals on their orientation and temperature in tension are discussed. A method is proposed for attaining a high yield strength in single-crystalline high-entropy (CoCrFeNi)(94)Ti2Al4 under tension at above 296 K.