Unveiling enhanced oxidation resistance and mechanical integrity of multicomponent ultra‐high temperature carbides

Abstract

The development of a new class of multicomponent ultra-high temperature ceramics (MC-UHTCs), often referred to as high-entropy UHTCs, has gained increased interest due to the possibility of improved thermomechanical and oxidation properties. In this study, a systematic approach by gradual addition in the UHTC components ranging from a binary to a dense quaternary (Ta,Nb,Hf,Ti)C is synthesized using spark plasma sintering (SPS). The solid solutioning was the critical factor in homogenizing the composition in the multicomponent system. The segregation of NbC and HfC was seen in binary and ternary UHTC systems, while a single-phase homogeneity was observed in the quaternary UHTC improving its hardness up to 34.8 GPa. The presence of closely spaced slip lines in the MC-UHTCs enhances resistance to indentation damage up to 72% at an applied load of 200 N. The formation of complex mixed oxide phase of Hf 6 Ta 2 O 17 ensued in the lower to negligible oxidation even up to 3 min of plasma exposure with temperature exceeding 2800 • C. In sum, though the entropy remains medium (0.96R) for the selected system, the quaternary UHTC system undoubtedly has significantly better thermomechanical performance when compared to established baseline UHTCs. This raises the debate on the justification for calling a multicomponent system a "high entropy" to be seen in a new light. The developed MC-UHTCs elicits the paradigm of this new class of UHTCs expanding their potential in thermal protection systems for hypersonic applications.

Fracture‐Resistant and Thermally Insulating Ultrahigh‐Temperature Carbide Foams

“…Due to the mutual solubility of UHTC carbides, a solid‐solution phase was expected to form during the sintering process. [ 9,10,28 ] Hence, the phase components of the procured raw powders, ball‐milled, and pressureless spark plasma sintering (PSPS)‐processed TaC–HfC sample were analyzed using an X‐Ray diffractometer (XRD, Rigaku Smart‐lab) using Cu K α radiation (λ = 1.54 Å) at a scan rate of 1° min −1 and step of 0.01°. The operating voltage and current for the instrument were set respectively to 40 kV and 40 mA in the 2° range of 20°–80°.…”

“…The chosen sintering parameters was based on the previous studies on SPS sintering of binary compound of TaC-HfC and multicomponent compound of TaC-NbC-HfC-TiC, which showed to form a single-solid-solution phase at 1850 °C for 10 min under application of 60 MPa pressure. [9,10]…”

“…Authors previously reported the solid-solution formation had been shown to improve the mechanical properties of UHTC carbides. [9,10] The solid-solution formation in multicomponent (MC)-UHTCs increases the ductility due to increased valence electron concentration (VEC). [45] The VEC increases from more covalent to metallic bonding leading to increased hardness.…”

“…Ultrahigh-temperature ceramics (UHTCs) can be potentially used for key thermal components such as nose cones and leading edges of hypersonic vehicles for a prolonged period while maintaining integrity and stability of structure and shape during service (>2000 °C). [5][6][7][8] UHTC carbides such as TaC and HfC, owing to the highest melting temperature reaching 4000 °C, [9,10] are potential materials for thermal protection systems (TPS) due to the thermal properties beyond the capabilities of existing structural materials. The bulk UHTC carbides intrinsically have very high lattice thermal conductivity (>30 Wm À1 K À1 ), which frustrates the thermal insulating field application.…”

High‐entropy (Ti0.2V0.2Nb0.2Mo0.2W0.2)Si2 with excellent high‐temperature wear resistance

“…Based on the results in 57 Meanwhile, lattice distortions (0.35) caused by the atomic size, electronegativity, and neighboring atoms can further make a contribution to the expected enhancement of hardness. 58 In assessing material hardness, nano-hardness is considered a superior metric to microhardness.…”