Electrochemical and mechanical behavior in polycrystalline CoNi-Ga shape memory alloys

Abstract

"Electrochemical behavior and microstructure was studied in polycrystalline Co38.3Ni32.1Ga29.6 alloy using the electrochemical technique of polarization curves in a medium of 3.5 wt % NaCl and 0.5M H2SO4. The importance of these alloys is due to their functional behavior, as shape memory alloys with ferromagnetic properties. The alloy was fabricated by induction furnace and the characterizations were performed using differential scanning calorimetry (DSC), nanoindenter tests and X-ray diffraction (XRD) The analysis of the kinetics of corrosion was conducted using cyclic sweep voltammetry curves with potentiostat/galvanostat. The corrosion morphologies were also analyzed by scanning electron microscopy (SEM). The kinetics of corrosion was found to be highest in the acid media and the alloy with thermal treatment in 3.5 wt% NaCl (A-TT-NaCl) shows a icorr lower that the alloy without thermal treatment (A-NaCl) in the same solution. On polarization curves, the current alloys exhibited a general dissolution in the anodic branch until certain potential was reached where a spontaneous passive zone occurred in 3.5 wt% NaCl media, similar behavior was found in acid media where, under high potentials occurs a repassivation zone at 427mV and elements such as Co and Ni were present in a higher percentage for all the corrosion deposits."