Temperature dependence of the microhardness of beryllium single crystals and Be-Cu alloys

In Vickers hardness tests with a pyramidal indentor, the microhardness of beryllium single crystals and Be--Cu alloys (0.23 and 1.34 at. percent Cu) along the c axis reaches values of 1000-1200 kg/mm/sup 2/ at low temperatures, which are comparable with the values for some crystals with covalent bonds. With increasing temperatures and alloying with copper the anisotropy of the microhardness decreases, but the absolute values remain high up to 400/sup 0/K. The high anisotropy of the hardness of beryllium is due to its lattice and not to the presence of impurities. The results obtained and previous results on the critical shear stresses in different slip systems indicate strong anisotropy of the bonding forces in beryllium crystals and beryllium alloys with copper.