The tetragonal compound Al3Zr can be transformed into the cubic Ll2 structure by additions of Cr, Fe, Ni or Cu. This result is interpreted in terms of Pettifor’s structure map. The transformation is accompanied by substantial softening. The significant porosity of cast buttons which develops during the homogenization required to produce the Ll2 structure is attributed to the Kirkendall effect. Al-5.5Fe-25Zr (at. %) specimens with the Ll2 structure can be deformed at room temperature in compression, and their yield stress has been determined as a function of temperature. Al-Fe-Zr is nevertheless a brittle material. This is illustrated for Al-Fe-V-Zr Ll2-structure compound, the fracture toughness of which is only slightly higher than that of sintered SiC. Evidence is presented to suggest that Ll2 formation is accompanied by an increase in toughness. Significant improvements in the mechanical properties of Al3Zr-type alloys may possibly be achieved by improved processing.
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Schneibel, J.H., Porter, W.D. Microstructure and Mechanical Properties of Ll2-Structure Alloys Based on Al3Zr. MRS Online Proceedings Library 133, 335 (1988). https://doi.org/10.1557/PROC-133-335