Inherent internal friction of B2 → R and R → B19′ martensitic transformations in equiatomic TiNi shape memory alloy

The inherent internal frictions IFPTB2→R+IFI and IFPTR→B19′+IFI of Ti50Ni50 alloy are studied under isothermal conditions. The tan δ   values of IFPTB2→R+IFI and IFPTR→B19′+IFI are both proportional to σ0/υ1/2 and thus the damping mechanism of IFPTB2→R+IFI and IFPTR→B19′+IFI is related to the stress-assisted martensitic transformation and stress-assisted motions of twin boundary. The tan δ   value of IFPTR→B19′+IFI is larger than that of IFPTB2→R+IFI because of the larger transformation strain and the greater twin boundaries associated with the R → B19′ transformation.