Synthesis and Stability of Higher-Order Superstructure of Cubic Laves Phase in an Al-Cu-Ta alloy

Abstract

In this work, we investigated on the synthesis and stability of a ternary complex metallic alloy in Al-Cu-Ta system, close to the composition of Al_56.6Cu_3.9Ta_39.5. The Rietveld refinement of X-ray diffraction data established its structure to be FCC (space group: F$\overline{4 }$3m; lattice parameter, a = 45.339 (7) Å), which has been correlated with the seventh order superstructure (7x7x7) of imaginary cubic Laves phase (lattice parameter of it being close to 6.5 Å). After annealing at1400K for 24 h, the as-cast alloy exhibited the same type of intermetallic phase with the slightly reduced lattice parameter (a = 45.2908 (9)Å). However, no other major phases could be detected from the X-ray diffraction data in both the as-cast and annealed alloys. The microhardness tests showed a variation of hardness from 8.8 GPa to 7.2 GPa for annealed and 7.6 GPato 4.8 GPa for as-cast samples. The variation of hardness with load, known as indentation size effect, was found to be relatively less in the annealed sample compared to that of the as-cast one. No cracking is observed even at load of 1000 g implying the possibility of the limited toughness of this complex phase. Due to high hardness and high-temperature stability, this phase appears to have potential for applications as hard and tough coating materials.