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 unia xial compression are characterized using optical and electron microsco py. It is found that [001] orientation undergoes large homogeneous def ormation in the range of strain rates investigated (10(-2)-10(4)/s). E volution of dislocation substructure in [001] tungsten is characterize d by TEM studies. Under quasi-static loading rates, elongated dislocat ion 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, w ith the cell walls containing very high dislocation densities. The def ormation in [011] orientation is relatively less homogeneous under qua si-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 britt le manner.