Pressure Dependence of the Elastic Constants of Beryllium and Beryllium-Copper Alloys

The elastic constants of beryllium and of alloys containing 1.1 and 2.4 wt% copper (0.16 and 0.35 at.%) have been measured by a pulse-echo-overlap method. These stiffness coefficients in units of 10¹² dyn/cm² are: The effect of hydrostatic pressures up to 6 kbar is indicated by the pressure derivatives given below: The coefficient C₁₃=-0.01 is unusual for a metal; this value indicates that there is no coupling between a tensile stress along the c axis and a resolved stress in the basal plane. This anisotropy in the bonding mechanisms for the two principal directions has been correlated with the band structure and may account for the relatively easy cleavage of beryllium along the basal plane.