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EBSD analysis of dislocations on DC-Spark sample after heat treatment (1.040 C in H 2 , 2h)

EBSD analysis of dislocations on DC-Spark sample after heat treatment (1.040 C in H 2 , 2h). Anité Pérez Fontenla 28.01.2014. Aim of the study:.

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EBSD analysis of dislocations on DC-Spark sample after heat treatment (1.040 C in H 2 , 2h)

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  1. EBSD analysis of dislocationson DC-Spark sample after heat treatment (1.040 C in H2, 2h) Anité Pérez Fontenla 28.01.2014

  2. Aim of the study: • A deeper understanding of the dislocations role in the material response to the BKD’s could help us to understand why areas with same surface status are highly affected by the phenomena. • A crucial aspect is to find a diagnostic technique which determines their presence and/or density; • Dislocation presence (like a group concept) in the microstructure of the material can be studied using Electron Backscatter Diffraction (EBSD). This technique fulfills our following requirements: • Non destructive • Appropriate for 3D specimens • Provides a good combination of spatial and angular resolution • Relatively reduced time of data collection How?

  3. How? • If we focus an electron beam on a crystalline sample e- disperse beneath the surface, diffracting among the crystallographic planes. • The diffracted beam produces a pattern (EBSP) that can be imaged by placing a phosphor screen close to the specimen. EBSP are composed of intersecting bands (Kikuchi bands) that are directly related to the crystal lattice structure in the sampled region. Bands & dislocations? To accommodate plastic deformation, the material generates dislocations which disturbs the structure of the lattice and that leads in a reduction of bands quality 

  4. How? • That can be directly related with the residual strain and represented in a • local misorientation map. As BKD phenomena are complex and not well known, the density of dislocations will be studied with a simpler case: a hardness indentation.

  5. The average misorientation between every pixel and its surrounding pixels is calculated, and assigns the mean value to that pixel; Before micro-hardness test After micro-hardness test

  6. What’s next? Hardness indent nr2…successful! Check the reproducibility of the technique and obtaining statistics about the affected zone; Which part of the green area is due to dislocations and which one due to surface deformation? • interferometry? • AFM?

  7. Sub-grains or faceting?

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