Microstructural characterization and tensile behavior of reaction synthesis aluminum 6061 metal matrix composites produced via laser beam powder bed fusion and electron beam freeform fabrication

In this work, aluminum 6061-based powder blend feedstocks with reactive Ti-B/C additions were employed in two different additive manufacturing processes, laser powder bed fusion (L-PBF) and electron beam freeform fabrication (EBF3), to create micro- and nanoscale ceramic and intermetallic inoculants in situ and to examine the effect of feedstock inoculant content on microstructure and mechanical properties. Products of the reaction synthesis process were identified with X-ray diffraction and energy-dispersive spectroscopy to include Al3Ti, TiC, and TiB2. Electron back-scatter diffraction revealed significant grain refinement up to 74x, mitigation of solidification cracking, and formation of an equiaxed grain structure with the addition of just 2 vol.% inoculant. Inoculants formed in situ were seen to induce approximately 5x more grain refinement than pre-existing inoculants. The highest ultimate tensile strength and Young's modulus of 368 +/- 2 MPa and 92.8 +/- 1.6 GPa, respectively, were achieved at 10 vol.% inoculant in the L-PBF process. Strengthening mechanism calculations and the tensile data suggest a higher strengthening contribution via modulus mismatch and Orowan strengthening from the particles created by reaction synthesis than from Hall-Petch strengthening through grain refinement.

Automated summary

In this study, aluminum 6061-based powder blend feedstocks with reactive Ti-B/C additions were used in two additive manufacturing processes to create micro- and nanoscale ceramic and intermetallic inoculants in situ. The addition of inoculants led to significant grain refinement, mitigation of solidification cracking, and the formation of an equiaxed grain structure. The highest mechanical properties were achieved with 10 vol.% inoculant in the L-PBF process.