Phase transformation in oil-quenched Ni–21.2Al–20Fe alloy

Abstract

The internal friction ( Q −1) and the relative dynamic modulus (RDM) of the oil-quenched Ni–21.2Al–20Fe alloy were measured using a multifunctional internal friction apparatus by forced-vibration methods from room temperature to 200 °C. An internal friction peak is represented on the internal friction-temperature curve at about 113 °C during heating and the peak is shifted to about 38 °C during cooling for the oil-quenched alloy. The peak temperature does not change for different vibration frequencies during both heating and cooling, and therefore the peak is non-relaxational. It has been shown that the peak-heights decrease with increasing f and decreasing heating rate ( T ˙ ) and are linearly and directly proportional to T ˙ / f . DSC measurements show that there is an endothermal peak at 107 °C and an exothermal peak at 42 °C on the heating curve and cooling curve, respectively. Both temperature values are similar to those of the internal friction measurements during heating and cooling, respectively. XRD results show that the oil-quenched Ni–21.2Al–20Fe alloy possesses martensitic structures (L1 0) in addition to Ni 3Al and Ni 5Al 3. It can be deduced that the internal friction peak during heating is resulted from reverse martensitic transformation of L1 0 → γ and originated from martensitic transformation of γ → L1 0 during subsequent cooling. The internal friction peak height increases when Fe content is raised.