Microstructural Effect on the Superelastic Behavior of Polycrystalline NCAXB-Type Ferrous Alloys

Ferrous superelastic alloys are attracting considerable attention as a cost-effective promising candidate for smart materials. Through proper thermomechanical processing, Fe-Ni-Co-Al-X-B (X= Ta or Cr) alloys designed by CALPHAD methods with strong textures can show superelasticity. In heavily cold-rolled and solutionized NCAXB polycrystalline superelastic alloys, texture development was evaluated by EBSD, and the fraction of low-angle boundaries was determined. The tensile test results show that texture strength affects the superelasticity of NCAXB alloys. The microstructure evolution of grain boundaries is investigated before and after tensile tests, especially in the most strongly-textured samples. Differences in the superelastic behavior and properties of the Ta and Cr containing alloys will be compared, with advantages and disadvantages of each discussed. In addition, the grain size effect is also investigated in the current research. Through changing solutionization times, samples with different relative grain sizes (d/t, d—grain size, t—thickness of the sheet) show different superelastic strains. The relationship between relative grain size and superelastic strain will be demonstrated for NCAXB alloys.