Mechanical properties of superhard TiB2 coatings prepared by DC magnetron sputtering

Superhard titanium diboride (TiB2) coatings (Hv> 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB2 target using an unbalanced direct current (d. c.) magnetron. Polished Si (0 0 1), stainless steel, high-speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, Us, and substrate temperature, Ts, on mechanical properties of TiB2 coatings was studied. X-ray diffraction (XRD) analysis showed hexagonal TiB2 structure with (0 0 01) preferred orientation. The texture of TiB2 coatings was dependent upon the ion bombardment (Us increased from 0 to −300 V) and the substrate heating (Ts increased from room temperature (RT) to 700 °C). All TiB2 coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness Hv up to 34 GPa, effective Young's modulus E*=E/(1–ν) ranging from 450 to 600 GPa; here E and ν are the Young's modulus and Poisson's ratio, respectively, and elastic recovery We≈80%. TiB2 coating with a maximum hardness Hv≈73 GPa and E*≈580 GPa was sputtered at Us=−200 V and Ts=RT. Macrostresses of coatings σ were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB2 coatings exhibited compressive macrostresses.