Study On The Low Frequency Mechanical Relaxation In M18R Martensitic Transformations

Shape memory alloy is a new type of functional material studied widely in recent years that usually displays shape memory effect by means of temperature- or stress-inducted phase transformation. Cu-based shape memory alloy has been a focus due to its excellent function and low price, and its high performances are determined by thermo-elastic martensitic transformation. In the paper, the mechanical relaxation behaviors in the Cu-based shape memory alloy were studied to reveal the process of the thermo-elastic martensitic transformation and to expand its applications.Low-frequency mechanical relaxation technique is often used for studying various phase transformations because of its rich functions, high measuring accuracy and good physical coupling. In the experiments, Cu-Al-Ni-Mn-Ti alloy, etc. were adopted as experimental materials to systematically research the mechanisms and phenomena of the thermo-elastic martensitic transformation in forced vibration model, and especially to research its anelastic relaxation.It has been experimentally found that the internal friction peak measured in the thermo-elastic martensitic transformation of Cu-based shape memory alloy is actually composed of two independent phase transition peaks, i.e. low- and high-temperature peaks, which correspond to different mechanisms, indicating that the thermo-elastic martensitic transformation is a process coupled by multiple mechanisms. The low-temperature internal friction peak, arising from phase transformation modulus softening, shows a shift in temperature spectra with increasing frequency, but it does not accord with Arrhenius relationship; it symmetrically distributes and gets to some extent broaden at frequency spectra compared with Debye relaxation, and the relation of loss modulus to modulus relaxation quantity is M 2 = 0.316δM and semi-peak width isΔlog10ωτ=1.735 in the alloy. The theoretical analyses indicate the movement along phase interface relative to the low-temperature peak belongs to a kind of anelastic relaxation. The phase transformation relaxation time meets a same relationship to dynamic modulus. The modulus softening is biggest, while the relaxation time is shortest at 65℃.