Grain boundary engineering and phase structure control in CoNiAlFe shape memory alloys: Effects of deformation and heat treatment

This study examines phase evolution, chemical homogenization and recrystallisation in polycrystalline Co 35 Ni 35 Al 28 Fe 2 during hot rolling and annealing. Specimens were rolled at 800 or 1000°C to reductions of 50 or 75% and annealed at 800 to 1200°C. Combined BSE/EDS analysis and EBSD phase mapping identified a BCC/B2-type matrix and an FCC Co-rich γ phase. EBSD phase fractions ranged from 1.69 to 13.20% and closely matched BSE estimates. Annealing at 1000°C promoted static recovery, partial heterogeneous recrystallisation and localized grain growth. Increasing reduction from 50 to 75% changed grain size and GAM only slightly but markedly increased the FCC fraction. Annealing at 1200°C removed detectable Co-rich regions only after prior rolling, producing a homogeneous coarse-grained structure suitable for grain-boundary engineering.