Quantification of the amount of ɛ martensite in a Fe–Mn–Si–Cr–Ni shape memory alloy by means of electron backscatter diffraction

Abstract

The determination of the volume fraction of ɛ martensite is of crucial importance to study the shape memory behaviour of an iron-based shape memory alloy (SMA). Several techniques have been used in literature trying to obtain a reliable measurement of this volume fraction. The results of these attempts were, however, not satisfying. In the present work, the amount of ɛ martensite in a Fe–Mn–Si–Cr–Ni shape memory alloy was measured by means of electron backscatter diffraction (EBSD) before deformation, after deformation, and after subsequent annealing. Despite the specific nature of the austenite-to-ɛ-martensite transformation, which affected the image quality parameter, it was proven, through the high confidence index, that a correct indexing of the diffraction pattern of ɛ martensite is possible with this technique. The evolution of the ɛ martensite volume fraction could readily be followed with a reasonable accuracy, through the entire processing. These results showed that EBSD has a high potential to quantify the ɛ martensite fraction in an iron-based SMA.