Abstract
The relative stability of the different tri-aluminide (Al3M) phases in three binary systems (M = Zr, Nb and V) was assessed for their potential to form fine cubic L12 precipitates in additively manufactured alloys. Supersaturated thin films of Al-(8–30) at% M were sputtered and heat treated during in-situ x-ray diffraction (XRD) measurements to observe the temperature ranges of stability for each phase. As-sputtered films were then processed with laser tracks simulating additive manufacturing solidification conditions, and the formation of phases in the laser tracks was correlated with density functional theory (DFT) and nucleation rate calculations. We found that the metastable L12 structure is highly competitive with the stable DO23 structure in the Al-Zr system, but much less stable than the DO22 structure in the Al-Nb system, and both the DO22 and Al8V5 structure in the Al-V system. These experimental results were found to be in good agreement with the DFT and kinetic calculations, as we determined that the metastable L12 in Al-Zr only requires a small amount of undercooling to favor its nucleation over the stable DO23, suggesting additive manufacturing can be a viable pathway to develop Al-Zr alloys strengthened by a high volume fraction of L12 Al3Zr phase.
