Highly wear resistant dual-phase (Ti-Zr-Nb-Hf-Ta)C/(Ti-Zr-Nb-Hf-Ta) B₂ high-entropy ceramics

Wear characteristics of a fine-grained dual-phase high-entropy (Ti0.14Zr0.2Nb0.2Hf0.2Ta0.26)C + (Ti0.38Zr0.18Nb0.22Hf0.115Ta0.105)B2 were investigated using the ball-on-flat technique/dry sliding in air. The experimental material showed very high density with a value of 8.72 g/cm3 and a small grain size of HEC and HEB grains with values of 0.95 ± 0.30 and 0.99 ± 0.27 μm, respectively. The nano-hardness of the HEC and HEB grains is very high with mean values of 37.4 ± 2.3 and 43.0 ± 2.9 GPa, respectively with the micro-hardness of the dual system HV1 29.4 ± 2.0 GPa. The friction coefficient values during the test with 5 and 10 N increased from a value of 0.4 and reached the values 0.65 and 0.77 at the sliding distances of approximately 1500 and 1000 m, respectively. The specific wear rate decreased with increasing sliding distance at 5 N load, from 4.75 × 10−7 mm3/Nm to 4.2 × 10−7 mm3/Nm and at 10 N from 2.1 × 10−7 to 1.7 × 10−7 mm3/Nm. The dominant wear mechanisms in both cases were an oxidation-driven tribo-chemical reaction and tribo-layer formation in boride grains and mechanical wear in carbide grains.