Internal friction of B2 → B19′ martensitic transformation of Ti50Ni50 shape memory alloy under isothermal conditions

The inherent internal friction (IFPT + IFI)B2→B19′ of cold-rolled and annealed Ti50Ni50 alloy that exhibits B2 → B19′ martensitic transformation is studied under isothermal conditions. The tan δ value of (IFPT + IFI)B2→B19′ is proportional to σ0/ν1/2 and its damping mechanism is thus related to stress-assisted martensitic transformation and stress-assisted motion of twin boundaries. The tan δ value of (IFPT + IFI)B2→B19′ is smaller than those of (IFPT + IFI)B2→R and (IFPT + IFI)R→B19′ because the former shows no R-phase. The obliterated dislocations and defects after sufficient annealing can lower the tan δ value of the relaxation peak at about −60 °C.