EBSD study of angular deviations from the Goss component in grain-oriented electrical steels.
The magnetic properties of grain-oriented (GO) electrical steels strongly depend on the distribution of the α and β angles, i.e., the deviations of the easy magnetisation <100> from the rolling direction (RD) in the rolling plane and out of the rolling plane, respectively. However, most Electron Backscatter Diffraction (EBSD) studies consider the standard Goss deviation angle, which includes the rotation of the (110) plane about the RD. Therefore, in the present work, a new procedure is demonstrated for deriving the α and β angles from EBSD mappings to obtain a quantitative texture characterisation in line with the magnetic properties. This procedure is later applied to 37 GO steels after secondary recrystallisation that exhibit a wide range of permeability levels. The relation between the texture and the polarisation at 800A/m (J800) that is measured in the present study by EBSD is compared to the one that has been determined in previous papers with optical goniometers and X-ray diffraction techniques, and this relation is subsequently used to define a relevant parameter to describe the orientation quality of the grains. The results indicate that the average angle of the α and β deviations is a relevant deviation parameter for the characterisation of grain orientations. Finally, it is demonstrated that the combination of the quantitative correlation between polarisation and texture with the orientation imaging of EBSD offers the possibilities of both studying the crystallographic environment of highly oriented grains in the primary recrystallised matrix for the production of high-permeability steels and evaluating the spatial distribution of the angular deviations in GO steels after secondary recrystallisation.
Grain misorientations in theories of abnormal grain growth in silicon steel
Understanding of the texture selection mechanism in the abnormal grain growth in grain oriented silicon steel is crucial for the improvement of the production process and the quality of the product. Unfortunately, details of the phenomenon are not clear. There are two similar but competing views frequently repeated in the literature of the subject. The first one originates in the suggestion that the coincidence lattice (CSL) misorientation relationships are a factor in the secondary recrystallization in silicon steel [1,2]. Recently, an extended version of the ”CSL model” of abnormal grain growth is advanced [3–11]. Briefly, according to the model, the boundaries of Goss oriented grains are more frequently of the CSL–type than boundaries of other grains. Moreover, in the presence of precipitates, the CSL boundaries are assumed to be more mobile than general boundaries. Thus, the Goss grains have the opportunity to grow. The second view is based on the assumption that the high mobility is a feature of the so called ”high energy” (HE) boundaries defined there as boundaries between grains misoriented by the angle of 20 to 45◦ [12–19]. Again, the advantage of the Goss grains would come from the fact that they are bounded by the HE boundaries more frequently than other grains. The objective of this note is to discuss some aspects of those hypotheses, with special attention to the early stage of the secondary recrystallization. Our main concerns and some comments on grain misorientations in explanations of the abnormal grain growth phenomenon are listed in the next section.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.