TiNi基形狀記憶合金制振能及非晶質薄帶之研究
Studies on Internal Friction and Amorphous Melt-spun Ribbons of TiNi-based Shape Memory Alloys
Date Issued
2007
Date
2007
Author(s)
Chang, Shih-Hang
DOI
en-US
Abstract
The inherent internal friction (IFPT+IFI) of cold-rolled and annealed Ti50Ni50 alloy is studied under isothermal conditions. The tan δ values of two-stage (IFPT+IFI)B2→R and (IFPT+IFI)R→B19’ are both proportional to and thus the damping mechanism of (IFPT+IFI)B2→R and (IFPT+IFI)R→B19’ is related to stress-assisted martensitic transformation and stress-assisted motions of twin boundary. The tan δ value of (IFPT+IFI)R→B19’ is larger than that of (IFPT+IFI)B2→R because the larger transformation strain and the greater twin boundaries associated with R→B19’ transformation. The intrinsic internal friction IFI of R-phase and B19’ martensite are composed of static internal friction IFS and dynamic internal friction IFD. The tan δ values of IFSR and IFSB19’ are both proportional to and are related to the stress-assisted motions of twin boundaries. The tan δ values of IFSR are higher than those of IFSB19’ is owing to the softer storage modulus E0 in R-phase. The tan δ values of IFDB19’ are linear proportional to . The occurrence of relaxation peak at -60 oC is found to come from the IFSB19’, instead of the IFDB19’. The tan δ value of (IFPT+IFI)B2→B19’ is also proportional to and its damping mechanism is thus related to stress-assisted martensitic transformation and stress-assisted motion of twin boundaries. The tan δ value of one-stage (IFPT+IFI)B2→B19’ is smaller than those of (IFPT+IFI)B2→R and (IFPT+IFI)R→B19’ because the former shows no R-phase. The solution-treated Ti51Ni39Cu10 alloy displays a higher tan δ value and a wider transformation temperature range than cold-rolled and annealed Ti50Ni50 SMA because there are no cold-rolled defects or dislocations, as well as no Ti3Ni4 precipitates in the former.
As-spun Ti50Ni25Cu25 ribbon is fully amorphous with a lower wavenumber Qp than the amorphous Ti-Ni alloys owing to its high Cu content. Both crystallization activation energy Ea and onset temperature Tx for Ti50Ni25Cu25 ribbon are lower than those for Ti50Ni50 ribbon. When Ti50Ni25Cu25 ribbon is annealed at 500 oC for 3 min, the initial as-crystallized grains contain a low Cu content and perform a prominent shape memory effect. Through prolonging the annealing time, more grains are crystallized in the ribbon but it becomes more fragile and its recoverable strain decreases. This characteristic is due to the increasing Cu content in the crystallized grains. Crystallized Ti50Ni25Cu25 ribbon can exhibit a good shape memory effect only under appropriate annealing conditions. The Avrami exponent of Ti50Ni25Cu25 amorphous ribbons during isothermal annealing derived from the Johnson-Mehl-Avrami equation is about 3.0. This indicates that the main crystallization mechanism of Ti50Ni25Cu25 ribbons is interface-controlled three-dimensional isotropic growth with early nucleation-site saturation. According to the Arrhenius relation, the activation energy for crystallization is 314 kJ/mol. This value is similar to that obtained using the Kissinger method, which implies that the crystallization during continuous heating or isothermal annealing follows a similar crystallization mechanism.
Subjects
形狀記憶合金
麻田散體相變態
內耗
非晶質薄帶
結晶行為
Shape memory alloys (SMA)
Martensitic transformation
Internal friction
Amorphous ribbons
Crystallization
Type
thesis