Laser powder bed fusion enables exceptional design flexibility in metal additive manufacturing. However, a detailed microstructural analysis is crucial to fully understand its material performance and overcome challenges in process optimization. This thesis investigates the microstructural properties of the Al-1Fe-1Zr alloy (Constellium Aheadd® CP1) specifically tailored to the physical conditions of LPBF. The rapid solidification conditions inherent to LPBF promote the formation of metastable intermetallic particles, requiring high-resolution synchrotron-based 3D imaging for precise characterization. LPBF processing parameters significantly influence melt pool morphology, grain growth, and intermetallic formation. This work leverages nanoscale imaging at the ID16A Nano Imaging beamline of the ESRF to elucidate the spatial distribution of Fe- and Zr-rich intermetallics under different LPBF processing conditions and evolution during heat treatment. Investigations of prior melt pools show that a stable melt pool with a good width-to-depth ratio promotes well-defined columnar grain growth under moderate scan speeds with continuous wave laser mode, whereas increased scan speeds result in shallower melt pools. Pulsed wave modulation laser mode with higher energy density leads to deeper melt pools, disrupting columnar grain growth and increasing grain boundary density. HXCT and FXCT imaging demonstrate that Fe-rich intermetallics accumulate at grain boundaries, forming stable Al13Fe4. In contrast, Zr predominantly remains either trapped within the Al matrix or present as nanoscale L12-Al3Zr precipitates dispersed within the matrix. Quantitative analysis after heat treatment at 400°C/4h confirms a uniform background level of Fe (0.56 wt%) and Zr (0.96 wt%) concentrations. Meanwhile, overaging at 530°C/24h promotes intermetallic coarsening driven by Oswald ripening. Fe-rich intermetallics transform, with Al6Fe evolving into stable globular Al13Fe4 at grain boundaries and possibly transforming to Al3Fe within larger grains adopting rod-like morphology, while Zr remains in its nanoscale form, with partial transformation to the stable D023-Al3Zr at the grain boundaries and smaller spherical particles of the stable phase within the grains. First of its kind, high resolution FXCT quantification reveals that nano Zr-rich particles form 0.95% volume fraction (0.5wt%), while Fe-rich nanoparticles account for 0.03% (0.008wt%), suggesting that nearly half of Zr and only a fraction of Fe, are at this scale after overaging. This study establishes the capability of synchrotron 3D imaging to elucidate the nanoscale intermetallics and quantitative local elemental distributions. By refining high-resolution imaging techniques, this research contributes to the broader applications of advanced materials and additive manufacturing strategies.
Deepak Mani (Wed,) studied this question.