The five elastic constants of single-crystal Be0 were measured to determine their magnitude relative to those of other hexagonal materials and to enable a correlation with related properties. The pulse-echo method was used. The stihess constants are cil 4.70, c12 1.68, cis 1.19, c~r 4.94, and cM 1.53 x 1Ol2 dynes/cm2. These were related to the Young's, shear, and bulk moduli of polycrystalline BeO, the Debye temperature, and the repulsion term for the crystal energy.
Dislocations formed during the growth and deformation of BeO single crystals were studied with x-ray and electron microscopy. The stresses for slip on the systems (0001) 〈112̄0〉, {101̄0} [0001], {101̄0} 〈112̄0〉, and {112̄2} 〈112̄3〉 are approximately 3.5×108, 1.1×109, 4.9×108, and >2.5×109 dyn/cm2, respectively, at 1000°C. Slip directions in deformed specimens were shown with x-ray microscopy. Defects in the specimens were shown to interfere with slip. Dislocation pinning and elastic interactions were observed in electron micrographs. These observations are correlated with theory.
The flow and fracture mechanisms of well characterized hot-pressed polycrystalline Be0 were studied. Modulus of rupture tests were made from -1 9 6 O to 18OO0C on specimens of constant density and varying grain size. The fracture surfaces were studied with fractography and Xray rocking curves. Compression tests were performed both below and above the phase transformation temperature for B e 0 (2050°C). A model was developed for fracture below 1000°C, involving propagation of existing surface cracks through dissimilar barriers to form a crack front of irregular shape which generates dislocations near the tip. Above 1000°C a model of grain boundary sliding to open cracks at grain boundary junctions was indicated. Permanent deformation under compression was attributed to grain separation and void formation.
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