An ultrasonic prospecting of shape-memory alloy behaviour under thermal charges

Thermomechanical models may be produced to describe the macroscopic deformations of shape-memory alloys educated to be deformed with special shapes as a function of temperature. To be accurate, these models need to take into account evolution of the microstructure via homogenization theories. So, the aim of this work was to provide all available information about phase transformations occurring in the grain structures from an investigation close to the microscopic scale. In this work, we have visualized grain structures of Cu–Zn–Al duplex alloys using acoustic microscopy. Evolution of phase transformations as a function of temperature has also been followed on these acoustic images with a spatial accuracy up to few micrometres. This observation of sample surface has also enabled estimation of grain baring due to phase transformations. Using the same experimental device, acoustic signatures have been taken on samples in complete austenic or martensitic forms to measure the speed of Rayleigh surface waves. Despite the use of a wide ultrasonic frequency range from 15–600 MHz, it seems that wave attenuation due to viscosity is important and disables velocity measurements by this method. Finally, using an acoustic echographic technique, we have correlated attenuation and velocity of longitudinal waves to the global phase transformation of heated samples. © 1998 Kluwer Academic Publishers