Deformation induced intermediate metastable lattice structures facilitate ordered B2 nucleation in a fcc-based high entropy alloy

• Main Authors: Deep Choudhuri, Shivakant Shukla, Bharat Gwalani, Rajarshi Banerjee, Rajiv S. Mishra
• Format: Article
• Language: English
• Published: Taylor & Francis Group 2019-01-01
• Series: Materials Research Letters
• Subjects: High entropy alloys or Complex concentrated alloys; Bcc-ordered B2 precipitation; Structural models; Transmission electron microscopy; Deformation twinning
• Online Access: http://dx.doi.org/10.1080/21663831.2018.1553212

Ordered B2 precipitates typically nucleate at the grains-boundaries of fcc-based high entropy alloys. Here, we report a novel mixed-mode coupled displacive-diffusional transformation resulting in homogeneously distributed intra-granular B2 precipitates within the fcc matrix. Severe plastic deformation forms compositionally invariant, metastable distorted fcc structures, resembling hexagon-like templates, at the deformation twin-boundaries. These shear-induced hexagon-like templates correspond to the symmetry of the {111}bcc planes, and act as sites for B2 nucleation, establishing the fcc-bcc Kurdjumov–Sachs (KS) orientation relationship. However, the composition of these B2 precipitates is far-from-equilibrium. Subsequent isothermal annealing causes solute partitioning driving the composition of the B2 precipitates towards equilibrium.