48. Damping Characteristics of Shape Memory Alloys on Their Inherent and Intrinsic Internal Friction

In this chapter, damping characteristics of the inherent and intrinsic internal friction (IF_PT + IF_I) peaks for Ti₅₀Ni₅₀, Ti₅₀Ni_50-xCu_x, Ti₅₀Ni_50-xFe_x, Ni₂MnGa, Ni-Mn-Ti, and Cu-Al-Ni shape memory alloys (SMAs) are reviewed. Ti₅₀Ni₅₀ SMA exhibits obvious (IF_PT + IF_I) peaks with tan δ above 0.02 during martensitic transformations, but they only exist in a narrow and low temperature range. Ti₅₀Ni_50-xCu_x (x ≥ 10) SMAs show higher (IF_PT + IF_I) peaks than Ti₅₀Ni₅₀ SMA because B19 martensite in Ti₅₀Ni_50-xCu_x SMAs is originated by substituting Ni with Cu atoms while R-phase in Ti₅₀Ni₅₀ SMA is caused by the introduction of abundant defects/dislocations. Ti₅₀Ni₄₈Fe₂ and Ti₅₀Ni₄₇Fe₃ SMAs also exhibit higher (IF_PT + IF_I) peaks than Ti₅₀Ni₅₀ SMA because R-phase formation is due to the substitution of Ni by Fe atoms rather than induced by introduced dislocations. However, the martensitic transformation temperatures of Ti₅₀Ni_50-xFe_x SMAs are suppressed to lower temperatures simultaneously by the addition of Fe atoms. Ni-Mn-Ti and Ni-Mn-Ga magnetic SMAs both exhibit relatively high martensitic transformation temperatures. Unfortunately, the undesirable brittle nature of Ni-Mn-Ti and Ni-Mn-Ga SMAs critically limits their workability and high-damping applications. Cu-Al-Ni SMAs exhibit acceptable martensitic transformation temperatures and good workability; however, their (IF_PT + IF_I) peaks are relatively low. Among these various types of SMAs, Ti₅₀Ni₄₀Cu₁₀ SMA is more suitable for high-damping applications because it possesses the advantages of high (IF_PT + IF_I) peaks, adequate workability, and an acceptable martensitic transformation temperature near room temperature.