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 (100-300K) 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 150K. 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 "200K peak", earlier reported by many authors with non-intentionally H loaded NiTi alloys is confirmed to be a H-twin boundary interaction effect (PTWH).