Tensile deformation of beryllium single crystals in various orientations between 25°C and 600°C

Abstract

Single crystals of predetermined orientation have been grown from the melt by a floating zone technique using “seeds” to nucleate the required orientation. The crystals have been prepared from vacuum cast and extruded electrolytic flake of the highest commercial purity available. The level of purity obtained is 99.83% and the critical resolved shear stress for basal (0001) slip has been measured in tension from 25°C to 600°C, in crystals which have deformed only by basal (0001) slip. The critical resolved shear stress for (0001) slip remains constant at 750 p.s.i. in the temperature range 300° to 600°C and increases only × 5 in the range 300° to —196°C. This small rise in critical resolved shear stress contrasts markedly with that found for (101̄0) slip, which increases by × 9 in the same temperature range from ~ 1,500 to 13,000 p.s.i. By comparison with similar work 2 on metal 99.0% purity, it is concluded that increasing purity reduces the critical resolved shear stress for both (0001) and (101̄0) slip throughout the temperature range 25° to 600°C by ~ × 2. It is suggested that the independence of critical resolved shear stress for both (0001) and (101̄0) slip with temperature in the range 300° to 600°C implies that the beryllium lattice is hardened by increasing its solute concentration.