Large-Area EBSD Mapping 

Additive manufacturing (AM) technology is widely used in many industries, such as aerospace and medical, for its capability to produce complex 3D objects from digital models.

In this example, a Powder Bed Fusion in Selective Laser Melting process was used to produce austenitic stainless steel for implant technology. Selective Laser Melting SLM125 with a single 400W fiber laser was performed. Then, the sample was deformed according to DIN 50125 for tensile tests.

Investigating the spatial variations of twin boundaries and grain sizes within the material helps better understand the effect of manufacturing processes on the mechanical properties, e.g. strength and ductility, of the final product. For this, EBSD is an essential analytical technique which can be used to study the evolution of microstructure in metals and alloys.

Here, we perform a very large-area EBSD mapping after conventional tensile testing: in one single setup, the texture evolution is measured across the entire sample using an automatic sequential measurement of 500 maps of 240 million points in total. At the end of the measurement, data was automatically saved, the EBSD detector was automatically retracted and the beam switched off.

The optimum procedure for successful large-area EBSD mapping requires a planar sample with the signal setup done at the location where the EBSD pattern signal is the poorest, i.e. the area with the strongest deformation.

If the sample is not perfectly planar and there is no possibility to compensate the loss of focus during measurement, we suggest to setup the EBSD signal where it is poorest and at a medium topography. This method still works elsewhere when using our system for EBSD, QUANTAX EBSD, because it can index slightly saturated patterns.

The deformation mechanisms in austenite by slip and twinning are clearly visible in the ARGUS™ orientation contrast image (Figure 1) and in the EBSD orientation maps (Figure 2 and 3). In Figure 2, an abrupt change in the grain preferential orientation is visible (from green to blue in IPFx): a  certain value of the strain is reached that induces the maximum rotation angle for the specific initial orientation.¹ The same tendency is reported in deformed austenite for a strain of 14% during uniaxial tensile loading.²

If we zoom into the microstructure (Figure 3) we can see the boundaries distribution of a typical deformed austenitic steel.² The high density of Low Angle Boundaries (LAB) visible in this map is an indicator of the high cooling and strain rates experienced by the sample during the AM process and, respectively tensile test. The map also indicates the presence of a high fraction of Twin Boundaries (TB), which were formed during both manufacturing processes described above

[1]: Wansong Li et. al, Materials Characterization 163 (2020) 110282

[2]: K. Yvell et. al, Materials Characterization 135 (2018) 228-237

Sample courtesy of Dr.-Ing. Kristina Roder, Research assistant, Chair of Lightweight Structures and Plastics Processing, Technical University of Chemnitz (Germany).