Structure and mechanical properties of amorphous Ti-B-N coatings

In this investigation Ti-B-N-coatings were prepared on high speed steel and silicon substrates by reactive magnetron sputtering from a TiB2 target wit h a stepwise increase of the nitrogen how rate. Some samples were vacuum-an nealed up to 600 degrees C. All Ti-B-N layers had a dense structureless morphology, whereas the pure Ti B2 coating was crystalline and had a strong [001] fibre texture. The compos ition of the films was characterized by a nearly constant B/Ti ratio of 2.6 and a variable N/Ti ratio from 0 to 6.3. Consequently, the samples were si tuated in two different ternary phase regions. With the increasing nitrogen flow rate the measured compressive residual stresses and the hardness of t he Ti-B-N coatings decreased up to 50% in comparison with the TiB2, whereas the critical load of the adhesive failure was nor influenced. It could be detected that the amorphous state and the chemical composition were stable during annealing up to 600 degrees C. The compressive residual stresses had been reduced by thermally activated relaxation processes. The TiB2 coatings got tensile stresses, whereas in the Ti-B-N films the compres sive stresses were still present. Probably, ordering occurs in the amorphou s coatings, because their hardness increases by up to 40%. The results of s cratch tests were not influenced by annealing. (C) 1999 Elsevier Science S. A. All rights reserved.