Hypereutectic Al-Ce-X (X=Mn, Cr, V, Mo, W) alloys fabricated by laser powder-bed fusion

Abstract

We characterize the microstructures and high-temperature mechanical properties of Al-2Ce and ternary Al-2Ce-1X (at.%) alloys fabricated by laser powder-bed fusion (LPBF), where X = Mn, Cr, V, Mo, and W are slow-diffusing transition metals. All ternary alloys show a hypereutectic microstructure in the as-LPBF state, containing an interconnected network of eutectic Al₁₁Ce₃ phases (∼10 vol.%) and an additional population of submicron, equiaxed Al₂₀CeX₂ primary precipitates (∼10 vol.%) which are isomorphous among these five alloys. Similar microstructures are present in arc-melted rods and atomized powders but are coarser due to the slower cooling rates in these processes. The hardness of the as-LPBF ternary Al-Ce-X alloys (1300–1400 MPa) is higher than that of the binary Al-Ce alloy (∼1100 MPa) due to the higher volume fraction of strengthening phases. Furthermore, during exposure at 400 °C for up to three months, greater hardness retention is achieved in the ternary Al-Ce-X alloys (65–75%) than in the binary Al-Ce alloy (∼55%), which is attributed to the extreme coarsening resistance of the Al₂₀CeX₂ precipitates imparted by the very slow-diffusing ternary solute. These coarsening-resistant Al₂₀CeX₂ precipitates also substantially improve alloy creep resistance, increasing the threshold stress for dislocation creep at 300°C from ∼32 MPa for the binary Al-Ce alloy to ∼77–100 MPa for the ternary Al-Ce-X alloys, and at 400°C from <10 MPa for the binary Al-Ce alloy to >40 MPa for the ternary Al-Ce-V alloy.