Plasma FIB Sample Preparation for In-Situ Synchrotron Studies of Additively Manufactured Alloys

Why Traditional FIB Prep Fails for In-Situ Synchrotron Studies

Synchrotron imaging techniques like scanning X-ray fluorescence (s-XRF) require samples that are large enough to represent the overall material structure and precisely shaped for accurate measurements. Such precision can be achieved with FIB-SEM, while plasma FIB-SEM enables preparation of the larger sample dimensions required.

For precipitation studies in Al-Mn-Cr-Zr alloys, even minor gallium contamination can modify how precipitates behave near grain boundaries, producing misleading results during heat treatment.

Plasma FIB provides a cleaner alternative, enabling accurate, artifact-free tracking of microstructural evolution.

Large-Volume, Ga-Free Milling for Thermally Sensitive Alloys

The study focused on an Al-Mn-Cr-Zr alloy produced via powder bed fusion-laser beam (PBF-LB). A 10 mm³ bulk sample with >99.8% density was used. A site-specific lamella was extracted and thinned using the TESCAN AMBER X system with a Xe⁺ plasma ion beam, producing a sample approximately 10 µm tall, 30 µm wide, and 1 µm thick. It was mounted on a MEMS heating chip via Pt deposition.

The mounted sample was subjected to in-situ s-XRF imaging at the P06 beamline of the DESY synchrotron, where it underwent a simulated heat treatment with temperatures oscillating around 375 °C over a 24-hour period to monitor elemental movement.

Mn and Cr Precipitates Tracked with High Chemical Fidelity

s-XRF measurements revealed Mn-rich and Cr-rich precipitates forming along grain boundaries. Cr precipitates consistently formed near Mn phases, a behavior not observed in ex-situ studies. The as-printed melt pool microstructure remained unchanged, confirming thermal stability.

Crucially, the absence of Ga ensured that the grain boundary chemistry remained intact, allowing reliable interpretation of precipitate behavior. Plasma FIB also enabled larger lamella extraction with the exact dimensions required.