Carbon and titanium diboride multilayer coatings

Titanium diboride (TiB(2)) is a metal-based refractory ceramic material that has been investigated in industrial applications ranging from cutting tools to wear parts, and for use in the aerospace industry. The unique properties which make this material so fascinating are its high hardness, high melting point and its corrosion resistance. TiB2 is prevented from wider mainstream use because of its inherent brittle nature. With a view to overcome this in coating form and with the aim of providing in addition inherent lubricity, in this study, 50-layer TiB(2)/C multilayer stacks have been fabricated, with varying volume fractions of ceramic whereby the interfaces of the layers limit crack propagation in the TiB(2) ceramic. TiB(2) has been multilayered with carbon to make use of the unique and hybrid nature of the bonding in carbon coatings. DC magnetron sputtering with substrate bias was the preferred route for the fabrication of these coatings. AISI tool steel has been used as the substrate material. By varying the amount of TiB(2) ceramic from 50% to 95%, the hardness of the coating is seen to increase from 5 to 17 GPa. The hardness is observed to decrease as a function of increasing carbon content, agreeing with other studies that the carbon layers are not load bearing. The graphitic nature of the sp(2) bond, however, acts as a lubricant layer. (C) 2004 Elsevier B.V. All rights reserved.