Influence of Tantalum on phase stability and mechanical properties of WB2

Based on density functional theory, we recently suggested that metastable alpha-WB2 is a promising candidate combining very high hardness with high toughness. These calculations further suggested that the addition of Tantalum supports the crystallization of a-structured W1-xTaxB2-z, with only minor reduction in toughness. Thus, various Ta containing WB2-based coatings have been synthesized using physical vapor deposition. With increasing Ta content, the hardness increases from similar to 41 GPa (WB2) to similar to 45 GPa (W0.74Ta0.26B2). In situ micromechanical cantilever bending tests exhibit fracture toughnessK(IC )values of 3.7 to 3.0 MPa root m for increasing Ta content (single-phased up to 26 at.% Ta).