Crystallographic Analysis of Plate and Lath Martensite in Fe-Ni Alloys

In the present work, we use an advanced EBSD method to analyze the two prominent types of martensite microstructures that are found in the binary Fe-Ni system, lath martensite (27.5 at.% Ni) and plate martensite (29.5 at.% Ni). We modify, document, and apply an analytical EBSD procedure, which was originally proposed by Yardley and Payton, 2014. It analyzes the distributions of the three KSI-angles (xi(1), xi(2), and xi(3), KSI after Kurdjumov and Sachs), which describe small angular deviations between crystal planes in the unit cells of martensite and austenite-which are related through specific orientation relationships. The analysis of the angular distributions can be exploited to obtain high-resolution, color-coded micrographs of martensitic microstructures, which, for example, visualize the difference between lath and plate martensite and appreciate the microstructural features, like midribs in large plate martensite crystals. The differences between the two types of martensite also manifest themselves in different distributions of the KSI-angles (wider for lath and narrower for plate martensite). Finally, our experimental results prove that local distortions result in scatter, which is larger than the differences between the orientation relationships of Kurdjumov/Sachs, Nishiyama/Wassermann, and Greninger/Troiano.

Automated summary

In this study, an advanced EBSD method was used to analyze the two prominent types of martensite microstructures found in the binary Fe-Ni system, lath martensite and plate martensite. By modifying, documenting, and applying an analytical EBSD procedure, high-resolution, color-coded micrographs of martensitic microstructures were obtained, which visualized the differences between lath and plate martensite and appreciated the microstructural features.