Dependence on composition of the internal friction of Ni100−xTix alloys containing hydrogen

Low frequency (0.1–50 Hz) internal friction (IF) measurements have been made as a function of temperature (100–300 K) in the H-free and H-doped Ni50Ti50 and Ni52Ti48 alloys. In the H-free equiatomic alloy no IF peak occurs in the martensitic state, while hydrogen doping gives rise to a well developed Snoek-type relaxation within the martensite (B19′). In the Ni-rich alloy not undergoing martensitic transition, a well evident peak (PTWM) appears at around 150 K. H-doping cancels this peak and introduces an H Snoek relaxation in the B2 austenite. A recently reported peak associated with a sort of strain–glass transition occurring in Ni-rich NiTi alloys is shown to coincide with PTWM, while the “200 K peak”, earlier reported by many authors with non-intentionally H loaded NiTi alloys is confirmed to be a H-twin boundary interaction effect (PTWH).