Within the framework of the present study, we produced functionally graded (FG) Ti/TiC and Nb/NbC multilayered coatings using a magnetron sputtering system. The composition gradient was generated by varying the relative thickness of the as-deposited metal and carbide layers. Subsequent short diffusion treatments were aimed at eliminating the interfaces between the adjacent layers yet maintaining an overall carbon composition gradient across the thickness of the coating.

We were able to determine the diffusivities of carbon in the TiC layer at different temperatures and, hence, the activation energy, 132 kJ/mole, which is one third that for bulk activation energy. The diffusion coefficients were 3.5x10^-18- 5.7x10^-15 cm²/s for the temperatures range of 355-550°C. These values are significantly higher than expected from extrapolation of data obtained at elevated temperatures.

The triboligical properties were carried out on coatings consisting of graded Ti-TiC multilayers with different concentration profiles and that had been deposited on WC-Co substrates in two steps. First, 0.5µm thick graded Ti-TiC multilayers were deposited followed by a 2.5µm outer layer of stoichiometric TiC. A critical load ,Lc >27N in the as deposited and post annealed coating was observed for a Ti-rich profile The normal wear resistance in the Ti- rich profile was higher by one order of magnitude than for the other profiles.

The structural evolution of the Nb/NbC multilayers was carried at the temperature range of 400-800°C. At these temperatures, the changes of the relative amount of the phases present are due to the mobility of the carbon atoms. The Nb₂C structure was found to have an orthorhombic structure, in contrast to the expected from the phase diagram.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/7496 must be provided.

1. Microstructural evolution of reaction bonded boron carbide composites