Low-temperature densification of high-entropy (Ti,Zr,Nb,Ta,Mo)C—Co composites with high hardness and high toughness

Abstract

In order to prepare high toughness (Ti,Zr,Nb,Ta,Mo)C ceramics at low temperatures while maintaining high hardness, a liquid-phase sintering process combined with Co-based liquid-phase extrusion strategy was adopted in this study. The densification temperature can be lowered to 1350 °C, which is much lower than the solid-state sintering temperature (∼2000 °C) generally employed for high-entropy carbide ceramics. When sintered at 1550 °C and 30 MPa applied pressure, part of the Co-based liquid-phase was squeezed out of the graphite mold, such that only ∼3.21 vol% of Co remained in the high-entropy ceramic. Compared to the Co-free solid-state sintered (Ti,Zr,Nb,Ta,Mo)C ceramics, prepared at 2000 °C and 35 MPa, the hardness was slightly decreased from 25.06±0.32 to 24.11±0.75 GPa, but the toughness was increased from 2.25±0.22 to 4.07±0.13 MPa·m1/2. This work provides a new strategy for low-temperature densification of high-entropy carbides with both high hardness and high toughness.

A uniform rule between hardness and structure hierarchy of ceramics in both direct and inverse Hall–Petch regimes

“…The equipment for Vickers hardness testing is widely available and also applicable to a variety of hard and soft materials. 13,14 In most studies of ceramics, the Vickers hardness 𝐻 V is generally common and also the hardness index used in this work.…”

High‐entropy carbide‐based ceramic cutting tools

“…Three kinds of (Ti 0. 21 The as-sintered (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C 0.8 -based ceramics were machined into SNGN120408T02020 (ISO 9361-1: 1991) standard indexable inserts with the geometrical dimensions of 12.7 mm × 12.7 mm × 4.76 mm. The turning tests for the ISO C45E4 steel were conducted on a CNC lathe (ETC3650h, Shenyang Machine Tool (Group) Co., Ltd., China) under cutting conditions of 240 m/min cutting speed, 0.1 mm/rev feed rate, and 0.5 mm depth of cut.…”

“…The HEC2 sample was (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C 0.8 –15 vol% cobalt composite with high toughness (6.37 ± 0.24 MPa m 1/2 ) and low hardness (17.29 ± 0.79 GPa), which was densified by pressureless sintering at 1650°C for 60 min. The HEC3 sample was (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C 0.8 –7.7 vol% cobalt composite with high hardness (21.05 ± 0.72 GPa) and high toughness (5.35 ± 0.51 MPa m 1/2 ), which was prepared by a liquid‐phase sintering combined with cobalt liquid‐phase extrusion strategy; it was sintered at 1450°C for 10 min, and 4.3 MPa applied pressure by SPS; the synthesis procedures and the liquid‐phase extrusion mechanism have been reported in detail elsewhere 21 …”

A new route to fabricate high‐performance binderless tungsten carbide: Dynamic sinter forging

“…Several advanced sintering processes such as spark plasma sintering (SPS), 10 reactive SPS, 11 high pressure high temperature sintering, 12 and high frequency induction heating sintering, 13 have also been attempted to prepare the ultrafine-grained binderless WC. Although these processes can reduce the sintering temperature of binderless WC by comparison with the traditional sintering methods aforementioned, several specific shortcomings caused by themselves are certainly exist, 14 also it is difficult to scale-up the production. Take for example the most widely studied SPS process, which usually requires more than 1700 • C to approach full dense binderless WC, 8,15,16 although it has been reported in a few cases that nano/ultrafine grained binderless WC with relative densities higher than 99% can be sintered at ∼1500 • C. 17 The temperature of 1700 • C is still so high that grain growth and decarburization happen, 8,15 especially local overheating between the particles lead to abnormal grain growth due to grain boundary diffusion of nanoparticle agglomerates.…”