A TRANSMISSION ELECTRON-MICROSCOPE STUDY OF THE LONG-RANGE EFFECT IN TITANIUM NITRIDE AFTER METAL-ION IMPLANTATION

The improvement in the properties of tools and components after ion im plantation is the result of specific structural-phase states developed both in the implanted zone (IZ) and beyond into the implantation-affe cted zone (IAZ). The formation of defect structures beyond the implant ed zone is called the long-range effect and occurs both in metals havi ng high plasticity and low yield strength and in high-strength materia ls. In the present work, the microstructure of TiN coatings deposited by PVD and CVD methods is studied by transmission electron microscopy. Before dual implantation with Ni and Ti ions the PVD coating has a hi ghly non-equilibrium submicron crystal structure with a high level of local residual stress, whereas the CVD TiN coating has a microcrystall ine structure with low internal residual stress. Implantation into PVD TiN causes a relaxation of the local stress in the IZ and beyond. In contrast, in CVD TiN ion implantation leads to the development of subg rains, both within the IZ and immediately below it, in the IAZ of the coating. No additional phases are formed in either case. A possible me chanism for explaining the formation of the defect structure beyond th e IZ is introduced. This is based on the emission of a dislocation flu x from stress maxima developed at the IZ-IAZ interface in the form of mezo-bands. (C) 1998 Elsevier Science S.A. All rights reserved.