G-phase precipitation via electric pulse and its effect on the strength-ductility synergy

Abstract

This work investigates the effects of electric pulse treatment (EPT) on the microstructure and mechanical properties of cold-rolled 20Cr ferritic alloy, employing quasi-in-situ uniaxial tension, electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and atom probe tomography (APT). Uniaxial tensile tests indicate that an optimal strength-ductility synergy is achieved with pulse parameters of 420 A and 300 Hz, resulting in a tensile strength of 1250 MPa and an elongation at break of 7 %. Excessive peak current or frequency leads to a sharp decrease in strength, while lower current or frequency fails to restore ductility. Short-duration EPT significantly enhance hardness through the dense precipitation of superfine Ni₁₆Ti₆Si₇-G phase particles, while the coordinated deformation of lamellar and fine grains moderately improved ductility. Additionally, EBSD analysis during quasi-in-situ tension reveals that the fine grain zones between lamellar grains play a crucial role in work hardening, whereas the lamellar grains tend to undergo work softening at an earlier stage. The study concludes that EPT effectively enhances the mechanical performance of 20Cr ferritic alloy through G-phase precipitation, providing a promising approach for optimizing the strength-ductility balance.