The structure and properties of chromium diboride coatings deposited by pulsed magnetron sputtering of powder targets

Metal boride coatings are attracting increased interest, due to the fact that they combine high hardness with good wear and corrosion resistance. These coatings are often deposited by the sputtering of hot-pressed or sintered ceramic targets. However, targets of this nature can be prone to cracking and, since the user is limited to a single composition per target, do not offer the opportunity to readily vary film stoichiometry. Titanium and zirconium borides have been widely studied; however, chromium diboride is recognised as offering superior performance in corrosive-wear environments. In this study, therefore, CrB₂ coatings were deposited by the pulsed magnetron sputtering of loosely packed blended powder targets. This work was carried out in a deposition system specifically designed for the use of powder targets, and the effectiveness of this approach has been previously demonstrated through the production of a number of different multi-component coating materials. The CrB₂ coatings deposited exhibit extremely dense, defect-free, crystalline structures with high hardness (>30 GPa) and good corrosion resistant properties. This paper discusses the dependence of structure, mechanical properties and corrosion behaviour of such coatings on the DC pulsed plasma treatment conditions chosen.