(HfTiZrMnCr)B2 high entropy diboride ceramics: Synthesis mechanism, microstructural, mechanical and thermal characterization

This study explains the synthesis mechanism of (HfTiZrMnCr)B2 high entropy diboride ceramics prepared via a combined route consisting of ball milling and spark plasma sintering. Firstly, metal borides were in-house synthesized using mechanochemical synthesis and leaching processes under optimum conditions from metal oxides, B2O3 and Mg precursors. The (HfTiZr)B2 composition, chosen as the main composition, was hybridized with two different methods: planetary and vibratory ball milling. As a result of milling experiments, 6 h vibratory milling was determined as the optimum duration, and all compositions were produced by spark plasma sintering method (2000 °C, 30 MPa) following this optimum condition. Different compositions were used to see which one of the HfB2, TiB2, ZrB2 compounds acted as a host material. Based on the phase analyses, single-phase HEB structures, Ti-rich phases and Hf, Ti, Zr-oxides were observed in the microstructure. Detailed physical, microstructural, mechanical and termal characterizations were performed: the highest hardness values were observed in the (HfTiMnCr)B2 and (HfTiZrMnCr)B2 samples as ∼ 27 GPa, the lowest wear rate was recorded for the (HfTiZrMnCr)B2 sample as ∼2 × 10−6 Nm/mm3, and the highest oxidation resistance was achieved at the (HfZrMnCr)B2 and (HfTiMnCr)B2 samples as weight gains ∼ 1.90%