A Fundamental Study of Flow and Fracture in Beryllium
Final rept. 1 Jun 1976-31 Oct 1978
LOCKHEED MISSILES AND SPACE CO INC PALOALTO CA PALO ALTO RESEARCH LAB
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The effect of thermomechanical treatments on the grain size of HIP beryllium powder block and cast beryllium alloys has been studied. A grain-size controlled-fracture mode change has been observed in both powder-source and ingot-source beryllium. The mechanism of recrystallization in heavily deformed beryllium has been observed to be the in situ transformation of subgrains to grains by dislocation migration from grain interiors to grain boundaries. Beryllium which has been cold-worked and partly recrystallized to form some very fine grains was found to be much tougher than either unworked material or fully recrystallized material and approached the toughness of high-strength aluminum alloys. In upset-forged beryllium where the texture is similar to that of hot- pressed block, strength, ductility, and toughness were improved by partial recrystallization. The enhancement of ductility and toughness are believed to be a result of grain-boundary sliding in the regions where very fine grains occur. Transmission electron microscopy has been used to show the early stages of grain-boundary fracture and the grain-boundary dislocation structure preceding fracture. This work indicates that the use of rapidly cooled beryllium powder rather than impact ground powder would allow a further increase in ductility and toughness.
- Properties of Metals and Alloys