Modulation Effect of Hardness on the Friction Coefficient and Its Mechanism Analysis of ZrB2/Mo Multilayers Synthesized by Magnetron Sputtering

ZrB2/Mo multilayers were prepared by the magnetron sputtering technique on Si (100) and Al2O3 (001) substrates. The friction behavior and wear mechanism of the multilayers were tested at variable modulation ratios (tZrB2:tMo) of 1:1 to 8:1 at different temperatures. Under the influence of an effective modulation ratio and temperature, the friction coefficient and hardness of ZrB2/Mo multilayers showed an almost opposite change rule, that is, the higher the hardness, the lower the friction coefficient. The hardness and elastic modulus reached the maximum value (26.1 GPa and 241.99 GPa) at tZrB2:tMo = 5:1 and the corresponding friction coefficient was 0.86. Meanwhile, the hardness and average friction coefficient at 500 °C were, respectively, 8.9 GPa and 1.23. First-principles calculations of the interface model of ZrB2 (001)/Mo (110) showed that the ionic bonds and covalent bonds at the interface can effectively improve the viscosity of the multilayer and the stability of the interface, and thus increase the hardness. This also indicated that the variation of the friction coefficient was mainly determined by the stability of the interface in the ZrB2/Mo multilayers.