A Study on the Low Temperature Internal Friction Relaxation Peak in a Ti49.8Ni50.2 Alloy

The low temperature relaxation peak appearing around 200 K in Ti49.8Ni50.2 shape memory alloy is a multiple relaxation process with activation energy Q=0.39 eV and frequency factor f0=6.2 × 10^9 s^-1 and is associated with the interaction of dislocations with pinning vacancies. Due to the increase of dislocation density and the annihilation of quenched-in vacancies after thermal cycling, the height of relaxation peak PR decreases with increasing the number of thermal cycling. Higher amounts of dislocation-vacancy reaction cause a higher relaxation damping under the condition of higher quenching temperature. The quenched-in vacancies can have a significant effect on the transformation rate, and thus the heights of transformation peaks PH1 and PC1 decrease with increasing quenching temperature. Dislocations introduced by both thermal cycling and quenching from high temperature will depress the martensitic transformation, and hence decrease the peak temperatures of PH1 and PC1.