Analyzing 3D Microstructure of Hypereutectic Al-30Si Alloy With ZEISS X-Ray Microscopy

Phase contrast tomography for quantitative analysis

The creation of new alloys has mostly been a trial-and-error process. To create better metals, you need to characterize the microstructure which is greatly affected by material processing. Materials science microscopy has played a definitive role in the modern metallurgical development, but is now expanding to 3D.

Hypereutectic Al-Si alloys as engineering material

Contemporary high performance structural materials like hypereutectic Al-Si alloy is an attractive class of engineering material that finds application in many critical electronic purposes.  It’s attractive because it performs better than established alloys with desirable properties like low coefficient of thermal expansion, high electrical conductivity, and light weight.  However, the less desirable properties in these alloys are inherent brittleness, low formability, and catastrophic failure due to the presence of a coarse primary silicon phase which increases with the increase in silicon content.

3D microstructure of hypereutectic Al-Si alloy revealed by phase contrast tomography (ZEISS Xradia 520 Versa)

An international collaboration

To address this material design challenge, researchers at Naval Materials Research Laboratory (NMRL) in India used a novel approach of friction stir processing (FSP), a variant of severe plastic deformation process, for microstructural refinement.  In an international collaboration between the NMRL and ZEISS Microscopy, non-destructive three dimensional X-ray imaging, performed with ZEISS Xradia 520 Versa was used to investigate the microstructural modifications obtained by FSP on the Al-30Si alloy.

Unique phase tomography (propagation-based) was used to clearly discern and quantify the aluminum and silicon phases.  This is a challenge because of the low differences in the absorption coefficients of aluminum and silicon (e.g. neighbors on the periodic table), the two phases were very clearly discerned using the propagation phase contrast mode.  Consequently, quantitative analysis of the particle and voids was performed and resulting data shows the effectiveness of FSP in modifying the microstructure.

More information on the phase contrast capabilities of ZEISS Xradia 520 Versa and more including Laboratory Diffraction Contrast Tomography (LabDCT)

Read the full article in Microscopy & Analysis here

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