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.
Highlights
Ti-Ni alloys have important technological applications due to their unique properties of shape-memory and superelasticity [1]
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
This phase was 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
Summary
Ti-Ni alloys have important technological applications due to their unique properties of shape-memory and superelasticity [1]. Superelasticity is caused by the transformation induced by deformation under load, followed by the reverse transformation [4-5]. Use of these binary alloys is usually limited to applications where temperatures are lower than 100oC, because the temperature (MS) at which martensitic transformation begins is typically below 60oC. Alloys with high temperature shape-memory, with MS temperatures higher than 100oC, have been exhaustively studied due to their potential applications in various different areas. Examples are the high temperature ternary alloys TiNiZr and TiNiHf, which were developed with higher MS temperatures [6]
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