Exceptionally wear resistant (W_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)(C_0.75N_0.25) high entropy carbonitride

In the present investigation, the tribological properties of bulk high-entropy carbonitride (HECN) (W_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)(C_0.75N_0.25) were studied under dry sliding conditions at room temperature, with applied loads of 5, 10, and 25 N. The dense (relative density of 97.52%) and fine-grained (average grain size of 2.83 μm) ceramics exhibited a Vickers hardness (HV₁) of 23.45 GPa and an indentation fracture toughness of 2.73 MPa·m^1/2. These tribological properties are strongly dependent on the applied load. The coefficient of friction (COF) ranged from a stable value of 0.28 at 5 N to 0.38 at 25 N, and the specific wear rate increased from an exceptionally low value of 3.23×10⁻⁹ mm³/(N·m) at 5 N to 5.56×10⁻⁸ mm³/(N·m) at 25 N. A detailed analysis revealed that the dominant wear mechanisms evolve with increasing load: At 5 N, wear is governed by the formation of a protective amorphous carbon (a-C) layer directly on the surface; at 10 N, a transitional regime with a composite a-C/oxide layer is observed; at 25 N, wear is controlled by the formation and continuous disruption of a hard, abrasive oxide “glaze” layer. The ability of this HECN material to form adaptive tribolayers, resulting in outstanding wear resistance, highlights its significant potential for demanding applications.