Deformation behavior and microstructure of tantalum, and processing of carbon-tantalum carbide composites

Deformation behavior of TaC{dollar}sb{lcub}0.99{rcub}{dollar} at room temperature was studied by means of a combination of microindentation techniques and transmission electron microscopy. Extensive local plastic deformation was observed in the vicinity of microindentations. Plastic deformation of TaC{dollar}sb{lcub}0.99{rcub}{dollar} at room temperature was mainly accomplished by the motion of edge dislocations. Long screw dislocations and the wavy character of screw dislocations suggest the existence of a high Peierls stress for screw dislocation motion at room temperature. Annealing of the indentation-deformed TaC{dollar}sb{lcub}0.99{rcub}{dollar} results in strongly recovered microstructures and recrystallization, comparable to metals with high stacking fault energy.; Deformation behavior of TaC{dollar}sb{lcub}0.99{rcub}{dollar} polycrystals at elevated temperatures was investigated by compressive creep tests. From the results on creep tests at intermediate temperatures (1400-1500{dollar}spcirc{dollar}C) and stresses (105-170 MPa), the values of the stress exponent (n) and activation energy (Q{dollar}sb{lcub}rm c{rcub}{dollar}) for power-law creep of TaC{dollar}sb{lcub}0.99{rcub}{dollar} were found to be n {dollar}approx{dollar} 1.8 and Q{dollar}sb{lcub}rm c{rcub} approx{dollar} 150 KJ/mol. The low activation energy and the low stress exponent suggest that the creep of TaC{dollar}sb{lcub}0.99{rcub}{dollar} at intermediate temperatures is mainly controlled by grain boundary sliding. This is further supported by observation of void formation. The observation of dislocation interaction in the crystal interior suggests that dislocation glide may act as a minor contributing mechanism during creep. TEM investigation also revealed the formation of subboundaries and dislocation networks. Most dislocations formed during creep of TaC{dollar}sb{lcub}0.99{rcub}{dollar} have no preferential orientation, in contrast to dislocations formed at low temperatures.; The fabrication of C-fiber reinforced TaC composites was studied using combinations of powder metallurgy techniques such as cold pressing, slurry infiltration, sintering, and hot isostatic pressing (HIP). The characteristics of the interface between carbon fibers and TaC were investigated by optical microscopy, scanning electron microscopy and auger electron spectroscopy. No chemical reaction occurred at the interface between carbon fibers and a stoichiometric TaC matrix. Carbon fibers suffered damage by indentation from tantalum carbide particles during cold compaction and HIP. A tantalum carbide coating of C-fibers prevented this indentation damage.