Processing and Properties of High-Entropy Ultra-High Temperature Carbides

By E. Castle, T. Csanádi, Salvatore Grasso, J. Dusza, Michael J. Reece. Scientific Reports, 2018

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Bulk equiatomic (Hf-Ta-Zr-Ti)C and (Hf-Ta-Zr-Nb)C high entropy Ultra-High Temperature Ceramic (UHTC) carbide compositions were fabricated by ball milling and Spark Plasma Sintering (SPS). It was found that the lattice parameter mismatch of the component monocarbides is a key factor for predicting single phase solid solution formation. The processing route was further optimised for the (Hf-Ta-Zr-Nb)C composition to produce a high purity, single phase, homogeneous, bulk high entropy material (99% density); revealing a vast new compositional space for the exploration of new UHTCs. One sample was observed to chemically decompose; indicating the presence of a miscibility gap. While this suggests the system is not thermodynamically stable to room temperature, it does reveal further potential for the development of new in situ formed UHTC nanocomposites. The optimised material was subjected to nanoindentation testing and directly compared to the constituent mono/binary carbides, revealing a significantly enhanced hardness (36.1 ± 1.6 GPa,) compared to the hardest monocarbide (HfC, 31.5 ± 1.3 GPa) and the binary (Hf-Ta)C (32.9 ± 1.8 GPa).

Subfields: Mechanical Engineering, Mechanics of Materials

View Paper: https://www.semanticscholar.org/paper/28ad7fa02a9289f40e417b13c65296038857a068

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Citations in the corpus

• Part I: Theoretical predictions of preferential oxidation in refractory high entropy materials (2020, background): “0 Background and Introduction High entropy metals and ceramics, which are solid solutions consisting of four or more principal components are a new paradigm in materials design [1–6], and are of interest due to the large number of compositions that can be formulated and explored.”
• First-principles study, fabrication and characterization of (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramics (2019, neutral): “with their constituent metal carbides [9-13].”
• From high-entropy ceramics to compositionally-complex ceramics: A case study of fluorite oxides (2019, background): “tions of five or more principal cations, which usually produce >1.5 R per mol. ideal configuration entropy ∆����� , on at least one sublattice. However, like in the metallic HEAs, some researchers [13] also consider equimolar, four-cation compositions (with 1.39 R per mol. ∆����� ) as HECs. Here,”