EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High entropy alloys or complex concentrated alloys have stretched the limits of mechanical properties like yield strength, ductility and fracture toughness over a wide range of temperature and strain rate for metallic materials in the recent past. Newly developed two phase Fe50Mn30Co10Cr10 alloy with FCC austenite (γ) phase and HCP martensite (ε) phase is characterized by γ to ε transformation during deformation contributing to transformation induced plasticity. Recent investigations have shown that the transformation is bidirectional in nature and it is expected that the novel bidirectional-TRIP (B-TRIP) effect can be exploited to achieve better performance of the alloy. The present investigation aims to study the bidirectional transformation and its effect on the mechanical properties in compression for the dynamic and quasistatic strain rate regime. Preliminary results indicated substantial strain rate hardening with higher flow stress for dynamic deformed samples (strain rate of 1200-3200 s-1) compared to quasistatic deformed sample (strain rate of 10-3 s-1) accompanied with significant increase in volume fraction of the martensite phase for quasistatic deformed sample. Detailed microstructural characterization using EBSD provided evidence of reverse transformation from martensite to austenite phase in the dynamically deformed samples which showed insignificant change in the volume fraction of the two phases. The forward and reverse transformation is driven by synchronous motion of partiial dislocations in the FCC and HCP phase and is extremely sensitive to the local temperature, defect density and stress state. It is expected that higher defect density, heterogeneous stress state and adiabatic temperature rise during dynamic deformation favour reverse transformation contributing to not just higher strength but also higher ductility in Fe50Mn30Co10Cr10B-TRIP HEA in dynamic strain rate regime. A mechanistic perspective on the strain rate dependence of the bidirectional transformation will be discussed.