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

Abstract

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 (ξ1, ξ2, and ξ3, 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.

Local Maxima in Martensite Start Temperatures in the Transition Region between Lath and Plate Martensite in Fe-Ni Alloys

“…The EBSD data were evaluated following the approach which was recently documented in Ref. [ 8 ] and implemented into the MATLAB [ 60 ] toolbox MTEX [ 61 , 62 ]. In the present work, two procedures are used which were introduced in previous studies, see Ref.…”

“…Fe-Ni alloys are known to form two major types of martensite microstructures, lath martensite (LM, below 28.5 at.% Ni) and plate martensite (PM, above 28.5 at.% Ni). Excellent quantitative metallographic descriptions of LM and PM microstructures have been given in the literature (e.g., [ 7 , 8 ]). LM consists of fine longitudinal martensite crystals (laths), with regions of parallel crystallites and a homogenous distribution of lath sizes throughout the microstructure (e.g., [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ]).…”

“…Crystallographic orientation relationships between austenite and martensite have recently been discussed [ 8 , 57 ] and it has been shown how the austenite microstructure can be reconstructed from the martensite data using orientation imaging scanning electron microscopy (OIM, based on electron backscatter diffraction, EBSD). It has been previously shown how this method can be used to obtain high-quality images from martensite microstructures [ 8 ]. This method allows differentiation between different types of martensite through analysis of the details of the distributions of three deviation angles (the ξ-angles [ 8 , 57 ]).…”

“…It has been previously shown how this method can be used to obtain high-quality images from martensite microstructures [ 8 ]. This method allows differentiation between different types of martensite through analysis of the details of the distributions of three deviation angles (the ξ-angles [ 8 , 57 ]). In the present work, the technique [ 8 , 57 ] is applied to obtain microstructural and crystallographic information from the transition region between lath and plate martensite.…”

“…This method allows differentiation between different types of martensite through analysis of the details of the distributions of three deviation angles (the ξ-angles [ 8 , 57 ]). In the present work, the technique [ 8 , 57 ] is applied to obtain microstructural and crystallographic information from the transition region between lath and plate martensite. The present study was motivated by an unexpected finding in a binary Fe-Ni alloy with 28.5 at.% Ni.…”