Temperature dependence of elastic parameters and internal frictions for TiNi alloy

Using ultrasonics, TiNi's acoustic characteristics are observed in order to fully understand its memory effects. Longitudinal and transverse wave velocities, eight kinds of elastic parameters, and dilational and shear internal frictions are simultaneously measured as functions of temperature in cooling and heating runs between 223 and 374 K in TiNi alloy, using an ultrasonic pulse method. An abrupt decrease from around 300 K in Young and shear moduli, Debye temperatures and internal friction peaks during a cooling run shows a premartensitic TiNi-(II)/TiNi(III) transformation by electron-phonon coupling, accompanied by higher elasticity. A rapid decrease from around 250 K is observed in all four elastic moduli (Young, shear and bulk moduli, and Lame parameter) and Debye temperature and internal friction peaks indicate a TiNi (III)/disordered complex TiNi martensitic transformation due to a volume-nonpreserving deformation.