Evaluation of two-step transformation in Ni-rich titanium-nickel alloys using thermal and internal friction analyses

Abstract

The use of Ti-Ni memory alloys covers several fields of application such as medicine, dentistry, actuators,
sensors among others. Because of the thermomechanical behavior of these materials, they are an object of
continuous studies and their properties are related to the occurrence of thermoelastic martensitic phase transformations.
The thermal analyzes were performed using dilatometry and differential scanning calorimetry to
determine the temperatures that occurred transformations during the cooling and heating, as well as to evaluate
the influence of the thermal treatments performed by dilatometry. The thermomechanical behavior was
also evaluated by the internal friction that measured behavior damping considering the structural and microstructural
changes. The calorimetry measurements indicated suppression of the R phase through decomposition
of precipitates of Ti3N4after the thermal treatments, that were corroborated by dilatometry and microhardness.
This phase was also studied by the technique of internal friction, which showed that the mechanical
damping coefficient increased as a function of temperature, due to the movement of the defects induced by
tension.
Keywords: Ti-Ni, shape-memory effect, internal friction, dilatometry, calorimetry.