Structure of deposited and annealed TiB2 layers

TiB2 coatings were prepared on steer and silicon substrates by d.c. magnetron sputtering at different bias voltages. After deposition part of the coatings was vacuum annealed at 400 degrees C and 800 degrees C. Transmission elctron microscopic (TEM) investigations on cross-section-prepared specimens showed that the layers were nanocrystalline with an average diameter of columnar grains between 50 and 20 nm depending on bias voltage. The chemical composition of coatings was homogeneous within the layers and independent of bias. A non-stoichiometric B:Ti ratio was detectable and a high amount of Ar incorporation occurred. X-Ray phase analysis showed that the coatings consisted mainly of hexagonal TiB2 phase with strong (001) fibre texture. Moreover, high compressive stresses were measured which could be attributed to Ar incorporation. The microhardness, critical load and failure mode were influenced by high compressive residual stresses. After annealing at 400 degrees C the residual stresses were relaxed and the critical load was independent of bias voltage. After annealing at 800 degrees C an upwelling of the surface was observed connected with crack formations and the occurrence of three new phases. (C) 1997 Elsevier Science S.A.