Physical and thermophysical properties of a commercial Ni–Ti shape memory alloy strip

Abstract

Some physical properties like the thermal, thermomechanical, calorimetric, magnetic, and adhesive properties of a commercial shape memory alloy (SMA) with rectangular geometry were studied. Depending on the applied forces, there were identified range of elasticity, the elasticity–viscoelasticity coexistence domain, and the domain in which a maximum force of 18 N is applied, for the SMA strip. The controlled force module, in the tension mode, was used for the determination of the SMA strip elongation at application of the stretching forces from 0 to 13 N, at 30 °C, maintaining each static force value for 3 min. By employing the multi-frequency strain–stress modulus in the tension mode, DMA cyclic heating–cooling measurements were carried out. The measured dynamic mechanical properties for SMA strip were Storage Modulus, Loss Modulus, tanδ, and Stiffness, both at heating and cooling. Thus, the characteristic temperatures of the phase transitions (As, Af, Ms, Mf), of SMA strip were identified. Also, the values of the elasticity modulus (Young’s Modulus) of the SMA strip were calculated at 30 °C. With the DSC Q2000 device, using temperature-modulated differential scanning calorimetry method, a multi-step temperature variation program was applied to the rectangular strip in two stages (heating–cooling). Through the interpretation of heat fluxes (reversible, nonreversible, and total), the phase transitions in the formation of martensite, austenite, and also of the rhombohedral phase (R phase) and moreover enabled for the R phase identification, thermomechanical analysis confirmed the results obtained by classical DSC method. The adherence of some commercial azoic dyes on the rectangular SMA strip, as well as the modification of the surface roughness of the strip after the deposition of the dye, was also studied. By magnetic measurements, it was established that the SMA strip had magnetic properties at room temperature, in which magnetization is the sum of a superparamagnetic contribution and a paramagnetic term, linear in the intensity of the magnetizing magnetic field.