Formation and magnetic properties of butterfly-shaped martensite in an Fe–Ni–Cr alloy

The butterfly-shaped martensitic transformation has been examined by means of transmission electron microscope (TEM) and the magnetic properties of the alloy have been studied by using Mössbauer spectroscopy in an Fe–16.24%Ni–0.46%Cr (at.%) alloy. Mössbauer spectroscopy examinations showed that the austenite state is paramagnetic and butterfly martensite is ferromagnetic. The volume fraction changes, the effective hyperfine field of the ferromagnetic martensite phase and isomery shift values have also been determined by Mössbauer spectroscopy. In situ TEM studies were carried out in order to elucidate the nucleation and growth mechanisms of the martensite. The nucleation and growth of martensite is related to the motion of dislocations in austenite and this fact plays an important role in the kinetics of the martensitic transformation. Based on these experimental results, the nucleation and growth mechanisms of martensite crystals are discussed in detail.