Influence of sintering condition on tribological properties of (Hf-Ta-Zr-Nb-Ti)C carbides

The wear behavior of high-entropy (Hf-Ta-Zr-Nb-Ti)C ceramics (HECs) was investigated using the ball-on-flat linear reciprocating method/dry sliding in the air. The experimental materials were prepared by ball milling and spark plasma sintering at 2100 °C and 5, 10, or 20 min sintering time. The HECs achieved relative density from 99.5% to 99.9%, with homogeneous chemical composition and grain sizes of HEC from 8 μm to 11 μm. The sintering times showed no significant influence on the wear characteristics of the investigated specimens. However, very promising mechanical and tribological properties of HEC were obtained. The materials had Young's modulus from 452 GPa to 482 GPa, Vickers' hardness from 20.9 GPa to 22.0 GPa, and Indentation fracture resistance of ∼2.8 MPa·m1/2 - 2.9 MPa·m1/2. The measured values of specific wear rate varied from 1.18 × 10−6 mm3/N·m to 3.23 × 10−6 mm3/N·m and coefficient of friction under different loads were very similar, between 0.29 and 0.32. The dominant wear mechanisms in all cases were mild abrasion with limited oxidation-driven tribochemical reaction. •The prepared single-phase (HfTaZrNbTi)C systems showed very high relative density above 99%.•The chemical composition of the (HfTaZrNbTi)C grains was homogeneous without significant differences in the distribution of individual metal elements. Smaller defects were in the form of nanopores, which were mainly located at the grain boundaries.•The investigated high-entropy carbide ceramics exhibited excellent wear rates with an average value of ∼2.44 × 10−6 mm3/N·m. The highest wear resistance was of 1.18 × 10−6 mm3/N·m achieved a specimen sintered at 2100 °C for 20 min. The coefficient of friction values were very similar for the tested materials with average values of approximately 0.32 tested at 5 N and approximately 0.30 tested at 25 N.•The best combination of mechanical properties and wear characteristics for high-entropy (HfTaZrNbTi)C sintered at 10 min with high relative density 99.54% with an average grain size of 8.4 μm and very low porosity of 0.53%.