Spark plasma sintering synthesis of ReB2-type medium-entropy diboride (W1/3Re1/3Ru1/3)B2 with high hardness

TL;DR

This study reports the synthesis of a new medium-entropy diboride (W1/3Re1/3Ru1/3)B2 using spark plasma sintering, achieving high hardness and a uniform crystal structure, advancing materials for hard coatings.

Contribution

First synthesis of a medium-entropy diboride with a single phase and high hardness using spark plasma sintering of elemental powders.

Findings

Achieved a dense, single-phase hexagonal (W1/3Re1/3Ru1/3)B2 structure.

Obtained Vickers hardness up to 30.7 GPa at low load.

Discovered uniform atomic distribution of W, Re, and Ru in the lattice.

Abstract

A new medium-entropy diboride (MEDB) (W1/3Re1/3Ru1/3)B2 has been synthesized by spark plasma sintering of elemental powders at 1600 oC. Despite the dissimilar structures of WB2, ReB2 and RuB2, the sintered MEDB consists of a single hexagonal ReB2-type phase (space group P63/mmc) with a relative density of 94.2% and an average grain size of 6.8 $\pm$ 2.2 um. Structural refinement and electron microscopy measurements show that the W, Re, and Ru atoms occupy the same crystallographic site and are distributed uniformly in the lattice. The (W1/3Re1/3Ru1/3)B2 MEDB has Vickers hardnesses of 30.7 GPa at a load of 0.49 N and 20.5 GPa at a load of 9.8 N, which are comparable or higher than those reported for individual binary counterparts.