Influence of Tantalum on phase stability and mechanical properties of WB 2

Based on density functional theory, we recently suggested that metastable α-WB 2 is a promising candidate combining very high hardness with high toughness. These calculations further suggested that the addition of Tantalum supports the crystallization of α-structured W 1-x Ta x B 2-z , with only minor reduction in toughness. Thus, various Ta containing WB 2 -based coatings have been synthesized using physical vapor deposition. With increasing Ta content, the hardness increases from ~41 GPa (WB 2 ) to ~45 GPa (W 0.74 Ta 0.26 B 2 ). In situ micromechanical cantilever bending tests exhibit fracture toughness K IC values of 3.7 to 3.0 MPa-√m for increasing Ta content (single-phased up to 26 at.% Ta).