Automotive applications need low-cost, lightweight, high-temperature alloys to enhance efficiencies in systems such as internal combustion engines. The aluminum-iron-silicon (Al-Fe-Si) system provides an opportunity to develop such a material, as it comprises three of the lowest cost elements abundant in nature. Specifically, the τ₁₁-Al₄Fe_1.7Si (historically called τ₁₀) ternary intermetallic phase is a lightweight and low-cost phase with promising mechanical properties at high temperatures. However, the τ₁₁-Al₄Fe_1.7Si phase has a narrow compositional range, which should be expanded to use this alloy at a commercial scale. We expanded the phase boundaries of τ₁₁-Al₄Fe_1.7Si phase via alloy design and additive manufacturing to exploit the non-equilibrium nature of the solidification process. Additions of a quaternary solute X to the Al-Fe-Si ternary system were examined.

Using density-functional theory (DFT) calculations and refinement of neutron diffraction data, the crystal structure and preferred site occupation of the τ₁₁ phase were determined. The analysis of equilibrated alloys identified the phase boundaries of the τ₁₁-Al₄Fe_1.7Si phase. Combining computational tools such as DFT and thermodynamic calculations, a series of elements were identified as potential candidates to stabilize the τ₁₁-Al₄Fe_1.7Si phase. The solubility of these elements in τ₁₁ was determined experimentally by diffusion couple (DC) analysis. After a series of iterations between computational methods and strategic experiments, Mn was identified as a promising candidate to stabilize the τ₁₁ phase and increase its stability range. The stability and phase boundary of τ₁₁ with Mn additions was systematically studied using DFT calculations and the analysis of DCs and equilibrated alloys. DFT calculations reveal that Mn energetically prefers to occupy the 6h Wyckoff positions of the τ₁₁ structure and indicating complete miscibility between Fe and Mn in the τ₁₁ phase, this was then confirmed experimentally and a compositional range of τ₁₁-Al₄(Fe, Mn)_1.7Si of Al (25-0)Fe (12.8-7.6)Si (0-24.8)Mn in at.% at 800 °C was measured. The results demonstrate that the integrated framework of computational and experimental methods can identify pathways for the energetic and entropic stabilization of alloys, which can be applied to materials other than the τ₁₁ phase considered in this project.