The power of combining micro-and nano-analysis equipment

More complex multi-component metallic microstructures require the combination of different, yet complementary equipment. Discover the strength of combining instruments.

OCAS combined its high-end Field Emission Gun – Electron Probe Micro Analyser (FEG-EPMA), equipped with four Wavelength Dispersive Spectrometers (WDS) and a Soft X-ray Emission Spectrometer (SXES) detector, with its Field Emission Gun – Scanning Electron Microscope (FEG-SEM) and Electron Back-Scattering Diffraction (EBSD) detector. Whereas, EPMA-WDS is a micro-analysis tool providing the chemical distribution of elements, SXES is dedicated to trace analysis of light elements. As such, SXES is complementary to EPMA-WDS for carbon analysis. EBSD is a micro-analysis tool that identifies the orientation and phase identification of crystalline samples.

High image resolution, high spatial resolution, and high sensitivity

During the Austenite Reverted Transformation, Medium Mn steels depend on the stabilisation of austenite by Mn diffusion to obtain their excellent mechanical properties. The amount of austenite, and its morphology, location and stability greatly affect these properties. In-depth characterisation of micro/nanometre-sized austenite domains is challenging and requires our most powerful analytical tools.
Techniques combining high image resolution, high spatial resolution and high sensitivity are essential. We combined EPMA and EBSD analyses to correlate both chemical and structural information at the same location in the sample. High resolution C and Mn mappings acquired by EPMA-WDS are used to validate and improve the identification of the constituents (ferrite, martensite, austenite and pearlite) performed by EBSD. SXES is used locally to quantify the concentration of C.

An exhaustive picture of the microstructure

The comparison between EPMA and EBSD mappings shows that most microstructural features are consistently observed at the same location. Austenite domains (blue domains) on the EBSD phase map compare directly with carbon/manganese-rich domains evidenced by EPMA. Other carbon-rich phases such as pearlite or cementite particles can be found. These are known to modify mechanical properties. Although, usually invisible for EBSD, they are very well evidenced by EPMA, illustrating the power of combining structural with chemical analyses at the very same spot to reveal an exhaustive picture of the microstructure.
The amount of austenite as detected by EPMA is in good correlation with X-ray Diffraction measurements. Moreover, the general conclusions made from this study are well in accordance with equilibrium calculations.

“OCAS’s know-how and state-of-the-art equipment enable the interpretation of more complex multi-component metallic microstructures, raising product development to a new level.”

Mélanie Gauvin, Research Engineer Material Charcterisation & Testing, OCAS