Synthesis of high-entropy diboride TiZrNbHfTaB2 by vacuum-free direct current arc plasma method

Abstract

The study is the first to demonstrate the potential for synthesizing micro- and nanosized particles of high-entropy boride (HEB) TiZrNbHfTaB2 by vacuum-free electric arc method. Arcing induces the formation of carbon monoxide and carbon dioxide, providing a self-shielding effect of the reaction volume from atmospheric oxygen, which shifts the reaction towards boride formation. The synthesis product was identified as a solid solution with the AlB2-type hexagonal lattice, containing atoms of titanium, zirconium, niobium, hafnium, and tantalum. The lattice parameters of the HEB TiZrNbHfTaB2 phase were a = 3.1045 Å and c = 3.3775 Å. The analysis of the synthesis product revealed agglomerates of micron-sized particles consisting of individual particles, as well as nanosized particles. Bulk ceramic samples were fabricated by spark plasma sintering. The optimal sintering parameters were as follows: 2000 °C, 10 MPa, 5 min at a heating rate of 100 °C/min. Studies were conducted to determine the mechanical and thermophysical properties of the bulk HEB sample.