Calorimetry under stress. A preliminary study in single crystalline Cu-Zn-Al shape memory alloys

Abstract

A non-differential calorimetric analyzer was developed for an INSTRON 1123 machine (a stress-strain-temperature analyzer) with a temperature chamber INSTRON 1110. The study was performed using the Joule effect and pseudoelastic martensitic transformations in single crystals of Cu-Zn-Al alloys. The analysis of the system establishes that: the sensitivity of calorimetric measurements after a filter of two poles and two zeros is 166 mV W-1 (at 297 K), the noise is near 1.5 μV and the drift is close to 30 μV in 6 h. The reproducibility of the sensitivity working with one sample is better than ±0.3%, and the change to a new sample keeps the value below ±0.5%. The uncertainty in reproducibility in the martensitic transformation (including repositioning) does not overcome ±1.6%. The used calorimetric sensors limit the temperature to 373 K. The furnace control originated fluctuations on the base line (near ±20 μV), which by means of an auxilliary signal processing were reduced to 50% (less than ±10 μV).