High‐strength medium‐entropy (Ti,Zr,Hf)C ceramics up to 1800°C

Abstract

Medium‐entropy (Ti,Zr,Hf)C ceramics were prepared by hot pressing a dual‐phase medium‐entropy carbide powder with low oxygen content (0.45 wt%). The results demonstrate that the medium‐entropy (Ti,Zr,Hf)C ceramics sintered at 2100°C had a relative density of 99.2% and an average grain size of 1.9 ± 0.6 μm. The flexural strength of (Ti,Zr,Hf)C carbide ceramics at room temperature was 579 ± 62 MPa. With an increase in temperature to 1600°C, the flexural strength showed an increase up to 619 ± 57 MPa, and had no significant degradation even up to 1800°C. The high‐temperature flexural strengths of (Ti,Zr,Hf)C were obviously higher than those of the monocarbide ceramics (TiC, ZrC, and HfC). The primary strengthening mechanism in (Ti,Zr,Hf)C could be attributed to the high lattice parameter mismatch effects between TiC and ZrC, which not only inhibited the fast grain coarsening of (Ti,Zr,Hf)C ceramics, but also increased the grain‐boundary strength of the obtained ceramics.

Ultra‐high strength medium‐entropy (Ti,Zr,Ta)C ceramics at 1800°C by consolidating a core‐shell structured powder

“…The pore at the grain boundary could extend along the grain boundary to form a crack of length equal to the sum of the pore size and the grain size. 24 Although the porosity of TZTC F I G U R E 4 Flexural strength as a function of temperature for TZTC ceramics, and compared to the results of TZTC-BM, TiC, 21 and ZrC 13 ceramic was higher than those of TZTC-BM and monocarbides, the pores of TZTC are mainly closed pores, and the pore size (about 0.2 ± 0.1 μm) is much smaller than the grain size (1.1 ± 0.4 μm). Therefore, the pores in TZTC may not deteriorate its room temperature flexural strength.…”

“…Figure 4 shows the flexural strength of TZTC and TZTC‐BM ceramics sintered at 2100°C and monocarbide ceramics (TiC 21 , ZrC 13 ) at 25−1800°C. The flexural strength of TZTC at room temperature (511 ± 52 MPa) is close to that of TZTC‐BM (552 ± 22 MPa) and slightly higher than that of ZrC (446 ± 46 MPa), TiC (427 ± 99 MPa).…”

“…The obtained TZTC powder was sintered by hot pressing at 1900−2100 • C for 1 h. The detailed carbon-thermal reduction and hot-pressed sintering of raw materials were reported in detail by Wang of the same group. 21 An oxygen/nitrogen analyzer (Leco, TC-600C) was used to measure the oxygen content in TZTC carbide powders. A X-ray diffraction analysis (XRD) was used to determine the phase compositions of TZTC carbide powders and ceramics with the Cu-Kα radiation, and refinement their lattice parameter by MDI Jade 5.0 software.…”

“…Binary oxides and graphite mixtures, TiO 2 , Ta 2 O 5 , graphite (named as TTOC), ZrO 2 , Ta 2 O 5 , graphite (named as ZTOC), were also mixed and heated up to 1400°C, to aid phase analysis for TZTC. The obtained TZTC powder was sintered by hot pressing at 1900−2100°C for 1 h. The detailed carbon‐thermal reduction and hot‐pressed sintering of raw materials were reported in detail by Wang of the same group 21 . An oxygen/nitrogen analyzer (Leco, TC‐600C) was used to measure the oxygen content in TZTC carbide powders.…”

“…After tested at 1800 • C, the structure of the medium-entropy carbide ceramic with a local chemical gradient was observed to undergo local decomposition. Wang et al 21 synthesized a dual-phase medium-entropy carbide powder with the oxygen content of 0.45 wt% and sintered a single-phase medium-entropy (Ti,Zr,Hf)C ceramic with a high density (99.2%) and a small average particle size (1.9 ± 0.6 μm) by hot-pressed sintering. The obtained (Ti,Zr,Hf)C ceramics have a very stable flexural strength (approximately 580−614 MPa) from 25 • C to 1800 • C. The purity and particle size of the original materials, sintering method, and the type and quantity of components may affect the mechanical properties of the sintered ceramic samples.…”