Experimental Evaluation of the Emissivity of a NiTi Shape Memory Alloy

In many applications of SMA (Shape Memory Alloys), the most appropriate way and sometimes the only way to measure the temperature is by means of thermography, which relies on knowledge of the emissivity of the material. This paper aims to evaluate experimentally the behavior of the emissivity of a NiTi shape memory alloy as a function of temperature to check how eventually the emissivity varies with the phase transformation. The SMA emissivity was determined by means of active and passive infrared sensors in the spectral band of 8 ~ 14μm in the temperature range of 25 to 100 ^oC under a vacuum of 30 kPa. The results show that the emissivity of SMA ranged around 15% during the heating cycle (the martensitic phase to the austenitic), and 24% in the cooling cycle. This variation corresponds to a variation between 3 and 5% in the value of the temperature measured