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Elemental Mapping of a Dispersion Layer on Steel

Thanks to its high sensitivity for light elements, investigating dispersion coatings on tool steels for the distribution and composition of boron phases is easy using QUANTAX WDS.

Dispersion hardening can be applied to produce hard and wear-resistant surfaces for industrial tools and high-temperature materials. This type of precipitation hardening relies on non-metallic inclusions, such as borides, to block structurally weakening dislocations in the metal.

The analysis presented here shows a cross-section of the interface of a Ni-P-B dispersion layer on steel substrate 100Cr6. Element distribution maps from this sample derived by simultaneous WDS/EDS acquisition at 5kV, 16 nA characterize different boron precipitates in the dispersion layer and steel contact zone. Whereas single-type Ni-B-phases have segregated from the dispersion layer, three types of Fe-(Ni-, P-)borides have grown in the alteration zone of the steel substrate close to the contact with the dispersion layer.

Mapping the 30 x 22 µm area with a resolution of 600 x 450 pixels was accomplished in only 10 minutes using QUANTAX WDS with diffractor BRML200 for boron determination.

Composite element distribution map of a Ni-P-B dispersion layer (top part) on steel substrate (bottom part). Sample courtesy of Ms. Nurul Amanina Binti Omar, HS Mittweida & TU Ilmenau. 
Overlay of SE image and boron X-ray intensity map acquired by WDS. Different boron phases, which are present in both areas, the dispersion layer and steel substrate, are shown in red.
Single element distribution maps of the same field of view as shown in precedings image for boron (WDS, upper left), phosphorus (EDS, upper right), iron (EDS, lower left) and nickel (EDS, lower right). 
Quantified map results showing selected element contents (wt%) in palette colors. From upper left to lower right: boron (WDS), phosphorus (EDS), iron (EDS) and nickel (EDS). 

Comparison of the Boron Signal in EDS vs. WDS

Single element distribution map of boron in steel interface acquired using SEM EDS
Single element distribution map of boron in steel interface acquired using WDS SEM

Thanks to its high sensitivity for low X-ray energies and improved counting statistics QUANTAX WDS can achieve better resolved map images. In this case acquisition time was only 5 minutes for both maps via simultaneous EDS and WDS acquisition.

QUANTAX WDS is a parallel-beam wavelength dispersive X-ray spectrometer optimized for the determination of low X-ray energies. With its grazing incidence optics, which capture X-rays close to the source or origin, and selected high efficiency multilayer diffractor elements for low energy X-rays, the QUANTAX WDS is much more sensitive to light elements than EDS. Compared to standard EDS (60 mm²), the signal intensity at 183 eV (B-Ka) is ca. 80 times higher with QUANTAX WDS, leading to fast and detailed mapping results.

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Automated Phase Identification

QUANTAX WDS is fully integrated into Bruker’s ESPRIT software, making it easy to combine WDS and EDS datasets for joint mapping and data analysis. Add-on programs such as AutoPhase can be applied to the ESPRIT HyperMaps containing both WDS and EDS data, for users who wish to visualize chemically similar or different phases in their SEM samples.

AutoPhase is based on multicomponent analysis functions and converts the elemental distribution map into a phase map, which is the most intuitive way to visually distinguish phases with different compositions in a mapped sample. Another advantage of AutoPhase is the determination of the area fraction for each phase in the mapped image area. 

Further Resources

Phase map calculated from the WDS/EDS X-ray intensity map. Legend for phases: Bor1 = Fe-boride, Bor2 = P-rich Fe-Ni-boride, Bor3 = Ni-boride, Bor4 = P-poor Fe-Ni-boride, Disp = Ni-P-B dispersion layer, Steel A = overprinted Ni-rich steel, Steel B = original 100Cr6 steel. The table presents the area proportions of the different phases.

QUANTAX WDS

QUANTAX WDS is a parallel-beam wavelength-dispersive X-ray spectrometer that is optimized for light element determination. The system is fully integrated in the ESPRIT software, allowing simultaneous acquisition and combined quantification with EDS. 

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