Damping Characteristics of the Inherent and Intrinsic Internal Friction of Ti<sub>50</sub>Ni<sub>50−</sub><i><sub>x</sub></i>Fe<i><sub>x</sub></i> (<i>x</i> = 2, 3, and 4) Shape Memory Alloys

Abstract

Ti50Ni50−xFex shape memory alloys (SMAs) have higher inherent and intrinsic internal friction peaks during R → B19′ transformation ((IFPT + IFI)R→19′) than during B2 → R transformation ((IFPT + IFI)B2→R). The reasons are that the former has the larger transformation strain and the abundant movable twin boundaries appearing in both R-phase and transformed B19′ martensite. Ti50Ni50−xFex SMAs also exhibit higher (IFPT + IFI)R→19′ peaks than annealed Ti50Ni50 SMA after cold-rolling because the latter needs dislocations to be introduced to form R-phase, but the former does not. For Ti50Ni48Fe2 SMA, the tan δ values of the (IFPT + IFI)B2→R and (IFPT + IFI)R→B19′ peaks and that of IFI in the R-phase regime decrease after the dehydrogenation treatment at 600°C for 6 h in a vacuum furnace, due to pinning of the twin boundaries by hydrogen atoms. However, the hydrogen pinning effect is small for IFI in B2 phase and B19′ martensite. Ti50Ni50−xFex SMAs with x = 2 and 3 at% have quite good (IFPT + IFI)R→19′ tan δ values (> 0.035), but their low transformation temperatures may restrict their use in practical high-damping applications.