Microstructure and properties of nitride and diboride hard coatings deposited under intense mild-energy ion bombardment

The concept of low or mildly energetic but intense ion bombardment was applied to coatings based on the nitrides and diborides of the transition metals titanium and zirconium. Coatings were deposited using non-reactive unbalanced d.c. magnetron sputtering. Films were bombarded by means of argon ions with varying energy (E-i) and intensity (ion/atom flux ratio J(i)/J(a)). Fracture cross-sections revealed the existence of the transition zone (zone T) structure for all coatings. TiN and ZrN coatings, which are exposed to low energetic bombardment, revealed a preferred growth on (111) lattice planes. Mildly energetic and intense bombardment resulted in a shift of the preferred orientation to (100). TiB2 and ZrB2 films grow more or less randomly under low energetic and less intense bombardment. However, they displayed a preferred (001) orientation with increasing intensity of the ion irradiation. The hardness of the coatings increased by the effect of both mildly energetic and intense ion bombardment, mainly as a result of reduced film porosity and to a lesser extent due to reduced crystal size and increasing film stresses. (C) 1999 Elsevier Science S.A. All rights reserved.