Oxygen concentration effect on substructure of molybdenum monocrystals grown by electron-beam zone melting

The substructure of single crystals of molybdenum obtained by zone melting has been investigated as a function of the oxygen concentration which has been determined by a neutron-activation analysis. The oxygen content in single crystals depends on its content in metalloceramic starting blanks, which, in its turn, is determined by the time of their hardening at 600 deg C prior to melting. A thorough cleaning of the starting materials lowers the oxygen concentration down to 0.5x10-2 %. It is shown that the increase in the oxygen concentration in the studied range from 1x10-3 to 9x10-3 % raises the dislocation density and the average disorientation angle, while decreasing the dimensions of subgrains and causing polygonization. In addition, oxygen affects the mobility of dislocations, consolidating them and promoting nucleation of new phase particles and giving rise to a mosaic structure of large disorientation angles