Mechanical behavior and fracture characterization of a monocrystalline Cu–Al–Ni subjected to thermal cycling treatments under load

Abstract

The mechanical behavior and fracture characteristics resulting from thermal cycling treatments under different applied loads were investigated in a monocrystalline Cu-13.5 wt.%Al-4.0 wt.%Ni alloy. The treatments consisted of 300 cycles in the temperature interval between 0 °C (close to M f) and 100 °C (above A f), under applied load conditions of 0.2 and 0.5 kg corresponding, respectively, to stresses of 11 × 10 − 2 and 28 × 10 − 2 MPa. Following each treatment, the specimens were tested in compression until fracture at room temperature. In addition to the compression results, the mechanical behavior was also evaluated by microhardness tests. Structural changes related to phase transformations were characterized by X-ray diffraction and the fracture characteristics were analyzed by scanning electron microscopy. It was found that the thermal cycling treatments promote significant changes in the structure due to a reversible martensitic transformation. An increase in the applied load results in a decrease in both the pseudo-yield and the total strain. It also results in a lower fracture resistance owing to additional deformation accumulated during the cycling treatment, which provokes the reversible martensitic transformation.