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 degrees 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 mu m to 11 mu m. 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 similar to 2.8 MPam(1/2) - 2.9 MPam(1/2). The measured values of specific wear rate varied from 1.18 x 10(-6) mm(3)/Nm to 3.23 x 10(-6) mm(3)/Nm 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.