PLASTIC-DEFORMATION OF CVD TEXTURED TUNGSTEN .2. CHARACTERIZATION

Deformation and failure modes of CVD textured tungsten in [001], [011] and random orientations subjected to various loading rates under uniaxial compression are characterized using optical and electron microscopy. It is found that [001] orientation undergoes large homogeneous deformation in the range of strain rates investigated (10(-2)-10(4)/s). Evolution of dislocation substructure in [001] tungsten is characterized by TEM studies. Under quasi-static loading rates, elongated dislocation cell formation is observed. At high strain rates, the dislocation density initially increases with respect to strain and then saturates when the temperature rise due to adiabatic heating becomes significant. At true strains beyond 2 the dislocations form well defined cells, with the cell walls containing very high dislocation densities. The deformation in [011] orientation is relatively less homogeneous under quasi-static loading, but under high strain rate loading the deformation is characterized by slip lines, extensive twinning and grain boundary cracking. Fine grain polycrystalline specimens fail in a typical brittle manner.