Aplicação de técnicas fototérmicas para o estudo da transição de fase de primeira ordem na liga NiTi

Abstract

In this work, Thermal Mirror spectroscopy (TMS), thermal relation calorimetry and Photothermal deflection spectroscopy (PDS) were used to detect and characterize the phase transition of the NiTi, normally known as Nitinol. The phases martensite, in ambient temperature, and austenite, in high temperature, were confirmed by X-ray diffraction. For comparison, the characteristics temperatures of the transition martensite-austenite were determined using the conventional techniques: DSC and the dilatometry, and compared with the obtained by Photothermal techniques. For the Thermal Mirror (TM), the behaviors of parameters θET and the thermal diffusivity, showed significant changes at the phase transition region, allowing the determination of their temperatures characteristics. Nevertheless, the behavior of these parameters is in agreement as expected comparing with the results obtained by the conventional techniques, quantitatively this obtained values, mainly for the thermal conductivity, show significant discrepancies, suggesting the necessity of consider the finite size of the sample, and the possibility effects of the anisotropy of the thermal and mechanical parameters on the model to describe the behavior of the superficial deformation induced by the local heat form the excitation beam. The thermal diffusivity behavior in the phase transition region obtained by TM, was confirmed using the Photothermal deflection spectroscopy modified. So far as we know, this is the first time that those techniques are applied for the metal material study in function of the temperature, in particular for the first order phase transition determination.