The determination of the volume fraction of e 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. The e martensite appears as thin lines in the optical microscopy. In TEM, the sequence of very thin lines forms an e band of only 0.4 µm thickness.

In the present work, the amount of e martensite in a FeMnSiCrNi shape memory alloy was measured by means of Electron BackScatter Diffraction (EBSD). Despite the specific nature of the austenite to e 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 e martensite is possible with this technique. The evolution of the e martensite volume fraction could readily be followed with a reasonable accuracy, through the entire processing: before deformation, after deformation and after subsequent annealing. These results showed that EBSD has a high potential to quantify the e martensite fraction in an iron based SMA.

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1. Determination of the recovery stress under constraint in Fe29Mn7Si5Cr SMA.