Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target

Zirconium diboride (ZrB2) exhibits high hardness and high melting point, which is beneficial for applications in for e.g. metal cutting. However, there is limited data on the mechanical properties of ZrB2 films and no data on epitaxial films. In this study, ZrB2(0001) thin films, with thicknesses up to 1.2 mu m, have been deposited on Al2O3(0001) substrates by direct current magnetron sputtering from a compound target. X-ray diffraction and transmission electron microscopy show that the films grow epitaxially with two domain types exhibiting different in-plane epitaxial relationships to the substrate. The out-of-plane epitaxial relationship was determined to ZrB2(0001)parallel to Al2O3(0001) and the in-plane relationships of the two domains to ZrB2[10 (1) over bar0]parallel to Al2O3[10 (1) over bar0] and ZrB2[11 (2) over bar0]parallel to Al2O3[10 (1) over bar0]. Mechanical properties of the films, evaluated by nanoindentation, showed that all films exhibit hardness values above 45 GPa, a reduced Young's modulus in the range 350-400 GPa, and a high elastic recovery of 70% at an applied load of 9000 mu N. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.