Damping Characteristics of the Inherent and Intrinsic Internal Friction of Ti₅₀Ni_50−xFe_x (x = 2, 3, and 4) Shape Memory Alloys

Abstract

Ti₅₀Ni_50−xFe_x shape memory alloys (SMAs) have higher inherent and intrinsic internal friction peaks during R → B19′ transformation ((IF_PT + IF_I)_R→19′) than during B2 → R transformation ((IF_PT + IF_I)_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. Ti₅₀Ni_50−xFe_x SMAs also exhibit higher (IF_PT + IF_I)_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 (IF_PT + IF_I)_B2→R and (IF_PT + IF_I)_R→B19′ peaks and that of IF_I 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 IF_I in B2 phase and B19′ martensite. Ti₅₀Ni_50−xFe_x SMAs with x = 2 and 3 at% have quite good (IF_PT + IF_I)_R→19′ tan δ values (> 0.035), but their low transformation temperatures may restrict their use in practical high-damping applications.