Formation of Cubic Ll2 Phases from Al3Ti and Al3 Zr by Transition Metal Substitutions for Al

Abstract

AbstractAlloys of (AlxM1−x)3Ti where M is V, Cr, Mn, Fe, Co, Nb, W, Fe + Ga or Fe + Ga + Mn were fabricated to form the Ll2 cubic phase, tested for ductility, and characterized by lattice parameter, microstructure, quantitative phase analysis, and phase composition. The elements V, Co, Nb, W, Fe + Ga and Fe + Ga + Mn are hereby newly found Ll2 formers in Al3Ti. Both X-ray diffraction and microprobe analysis were used to identify the phases, their volume fractions and compositions. The amount of ternary addition found in the Ll2 cubic phase varied between 4 and 12 atomic percent. This amount of ternary addition decreased as the atomic radius of the elemental addition increased. Pettifor's Mendeleev number was a useful guide in the selection of elements to form the Ll2 phase but did not correlate strongly with the amount of the ternary addition. For the DO23 phase of Al3Zr, the elements V, Mn, and Co were added to the list of Ni, Cu, Fe, and Cr as elements known to form the Ll2 phase. Little if any ductility was observed in these cubic Ll2 phases which readily cleaved with transgranular failure. To achieve ductility and toughness, more than transformation of these compositions from a lower to a higher symmetry crystal structure will be required.