Grain size dependence of pseudoelasticity in polycrystalline Cu-Al-Mn-based shape memory sheets

The effects of grain size on the stress-strain characteristics of Cu-Al-Mn-based pseudoelastic (PE) sheet specimens with various relative grain sizes d/t (d = grain size, t = sheet thickness) were investigated using cyclic tensile testing. The stress-strain characteristics such as the yield stress σ_y, work-hardening rate dσ_PE/dε and stress hysteresis of pseudoelasticity Δσ decreased, and the obtained maximum PE strain εPEMAX increased with increasing d/t. The σ_y, dσ_PE/dε, Δσ and εPEMAX plots as a function of d/t were divided into three regions. The critical points dividing the plots into the three regions were located at d/t ≈ 1 and d/t ≈ 2. These results can be explained from the standpoint of constraints between grains, depending on grain structure such as a fine equiaxed grain structure, a columnar-like grain structure and a fully columnar grain structure.