Creep of Beryllia Single Crystals

Abstract

The compressive creep behavior of single-crystal B e 0 was studied under inert atmosphere. The steady-state creep behavior was highly anisotropic because of easily activated basal slip. Crystals compressed along a [1101] axis deformed at temperatures as low as 650°C, whereas [1100]-aligned crystals showed comparable strain rates at temperatures 2 1650°C. The measured activation energies and stress exponents for creep were 371 kJ/mol and 4.65 f o r j h e [1101] alignment and 496 kJ/mol and 3.39 for the [1100] alignment, respectively. The precise mechanisms controlling creep behavior were not determined. Only one semiquantitative data point was obtained for the [OOOl] alignment, which indicates that the creep rate at 100 MPa and 1750°C is less than that for c-axis sapphire. [

Dislocations in Ceramics

“…At 1000 C, the yield stresses for these systems were as follows: 35 MPa for basal slip; 49 and 110 MPa for prismatic slip along h11 20i and ½0001, respectively; and >250 MPa for pyramidal slip. More recent studies on creep deformation in BeO single crystals by Corman [52] confirmed the anisotropic plastic deformation behavior; these studies also revealed that basal slip in BeO could be activated at surprisingly low temperatures. For example, at 50 MPa and using crystals with a high Schmid factor for basal slip (compression direction along ½ 1101), a creep rate of 1.3 Â 10 À7 s À1 was found at 650 C, which increased to 7.3 Â 10 À7 s À1 for a stress of 70 MPa.…”