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

EBSD analysis of dislocationson DC-Spark sample after heat treatment (1.040 C

in H2, 2h)

Anité Pérez Fontenla28.01.2014

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?

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.

How?

EBSP are composed of intersecting bands (Kikuchi bands) that are directly related to the crystal lattice structure in the sampled region.

To accommodate plastic deformation, the material generates dislocations which disturbs the structure of the lattice and that leads in a reduction of bands quality

Bands & dislocations?

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.

How?

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

What’s next?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?

=10 µm; Map5; Step=0.2 µm; Grid250x250

Hardness indent nr2…successful!

Sub-grains or faceting?