Sessile dislocations by reactions in NiAl severely deformed at room temperature

摘要

B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a〈1 0 0〉 carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a〈1 1 0〉 dislocations by dislocation reactions; the a〈1 1 0〉 dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a〈1 1 0〉 dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.