Kinetic grain growth, shape memory and corrosion behavior of two Cu-based shape memory alloys after thermomechanical treatment

Metallurgical and mechanical properties along with shape memory and corrosion behavior of Cu-11.8% Al-3.7% Ni-1% Mn and Cu-11% Al-5.6% Mn shape memory alloys (SMAs) were comparatively studied. The influence of grain refinement on the properties was studied by optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), potentiodynamic polarizations and bend and tensile tests. Static recrystallization and kinetic grain growth show a rapid recrystallization in the first 15 s of annealing at 800 degrees C followed by grain growths. The minimum grain sizes obtained after 15 s are 90 and 260 mu m for Cu-Al-Ni-Mn and Cu-Al-Mn, respectively. Tensile tests show typical three-stage curves for both alloys, and it is seen that alloys exhibit high fracture stress and strain after grain refinement. Microstructural observations show zig-zag morphology of beta(1)' martensite in the Cu-Al-Ni-Mn and coexistence of beta(1)' and gamma(1)' in the Cu-Al-Mn, which were confirmed by differential scanning calorimetry results. The shape memory ratios (eta) of the alloys before thermomechanical treatment, and after thermomechanical annealing at 800 degrees C for different time up to 15 min followed by water quenching, were evaluated. In addition, corrosion behavior of alloys after grain refinement was analyzed by means of potentiodynamic polarization measurements. The results showed that the anodic reactions were dominated by dissolution of copper, and Cu-Al-Ni-Mn alloy exhibits a better corrosion resistance than Cu-Al-Mn alloy.