Phase transformation behaviors of TiNi fibers embedded in an aluminum matrix

• A two-stage transformation behavior was observed when the value of prestrain was higher than 4%.
• Two kinds of martensite formed: stress-induced martensite and preferentially oriented martensite.
• The martensite re-orientated and variety of crystal defects formed with the increases of prestrain.
• The martensite fraction remaining in the fibers increased with the prestrain level increasing.

The effect of tensile deformation on the phase transformation behaviors of TiNi fibers which were embedded in a pure aluminum matrix was discussed in this paper. Differential scanning calorimeter (DSC) was used to study the martensite transformation. The microstructures of the TiNi fiber before and after tensile deformation were observed by transmission electron microscopy (TEM). Results show that martensite induced by stress preferentially nucleated at the grain boundary and the dislocation. When the amount of tensile deformation was higher than 4%, a two-stage transformation behavior was observed in the heating process. The peak appeared at low temperature correspond to the martensite induced by stress. While the peak appeared at high temperature correspond to preferentially oriented martensite. However, the martensite fraction remaining in the fibers increased with the prestrain level increasing because part of the martensite was deformed into fully detwinned preferentially oriented martensite, which cannot be detected by DSC.