Elastic moduli of the Laves-phase pseudobinary compounds Zr(AlxFe1-x)2 as determined by ultrasonic measurements

Ultrasonic methods have been used to measure the polycrystalline elastic moduli of the Laves-phase pseudobinary compounds Zr(AlxFe1-x)2 for 0.04x1.0. The bulk modulus decreases with increasing x up to the change from cubic (C15) to hexagonal (C14) structure at x=0.25. The shear modulus is essentially constant in the cubic phase. At the phase boundary the bulk modulus is about 6% higher in the hexagonal phase than in the cubic phase, while the shear modulus is the same in the two phases. As x increases in the hexagonal phase the bulk modulus decreases while the shear modulus increases. The softening of the bulk modulus in the cubic phase is correlated with the softening of the Fe bonding strength previously observed by nuclear methods, and with a sharp increase in the hydrogen capacity of these compounds. The stiffening of the shear modulus in the hexagonal phase may be correlated with the decrease of the hydrogen capacity in the corresponding compounds.