Article
Ultrahigh Temperature Flash Sintering of Binder-Less Tungsten
Carbide within 6 s
Huaijiu Deng
1
, Mattia Biesuz
2,3
, Monika Vilémová
2
, Milad Kermani
1
, Jakub Veverka
2
, Václav Tyrpekl
3
,
Chunfeng Hu
1
and Salvatore Grasso
1,
*
Citation: Deng, H.; Biesuz, M.;
Vilémová, M.; Kermani, M.; Veverka,
J.; Tyrpekl, V.; Hu, C.; Grasso, S.
Ultrahigh Temperature Flash
Sintering of Binder-Less Tungsten
Carbide within 6 s. Materials 2021, 14,
7655. https://doi.org/10.3390/
ma14247655
Academic Editor: Arkadiusz Gola
Received: 23 November 2021
Accepted: 7 December 2021
Published: 12 December 2021
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1
Key Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science
and Engineering, Southwest Jiaotong University, Chengdu 610031, China; Denghuaijiu9@outlook.com (H.D.);
miladkermani.mk@my.swjtu.edu.cn (M.K.); chfhu@live.cn (C.H.)
2
Institute of Plasma Physics of the Czech Academy of Sciences, Za Slovankou 3,
182 00 Prague, Czech Republic; mattia.biesuz@unitn.it (M.B.); vilemova@ipp.cas.cz (M.V.);
veverkaipp@cas.cz (J.V.)
3
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 8,
128 43 Prague, Czech Republic; vaclav.tyrpekl@natur.cuni.cz
* Correspondence: s.grasso@swjtu.edu.cn; Tel.: +86-184-8222-4962
Abstract:
We report on an ultrarapid (6 s) consolidation of binder-less WC using a novel Ultrahigh
temperature Flash Sintering (UFS) approach. The UFS technique bridges the gap between electric
resistance sintering (
1 s) and flash spark plasma sintering (20–60 s). Compared to the well-
established spark plasma sintering, the proposed approach results in improved energy efficiency
with massive energy and time savings while maintaining a comparable relative density (94.6%)
and Vickers hardness of 2124 HV. The novelty of this work relies on (i) multiple steps current
discharge profile to suit the rapid change of electrical conductivity experienced by the sintering
powder, (ii) upgraded low thermal inertia CFC dies and (iii) ultra-high consolidation temperature
approaching 2750
◦
C. Compared to SPS process, the UFS process is highly energy efficient (
≈
200 times
faster and it consumes
≈
95% less energy) and it holds the promise of energy efficient and ultrafast
consolidation of several conductive refractory compounds.
Keywords: tungsten carbide; ultrarapid consolidation; ultrahigh temperature flash sintering
1. Introduction
Over the past few decades, ultrafast sintering methods have reached a high degree
of sophistication. Shortening the consolidation time contributes to lower the energy con-
sumed during the firing process. Starting from the 1970s, high heating rates have been
exploited to enhance sinter ability while inhibiting the surface diffusion responsible for
grain coarsening [
1
,
2
] active in the early stages of sintering [
3
]. Sintering techniques as-
sisted by the application of an external electric field [
4
–
6
] allows ultrarapid densification
and out-of-equilibrium material processing [7–9].
In 2010, Cologna et al. [
10
] discovered that 3 mol% yttrium-stabilized zirconia (3YSZ)
can be sintered in a few seconds at 850
◦
C under an electric field of 120 V/cm. This process,
with heating rates in the order of 104 K/min [
11
], was named Flash Sintering (FS) and its
underlying mechanisms include: preferential overheating of the grain boundaries leading
to thermal diffusion [
12
] or localized melting/softening [
13
,
14
], fast-heating enhanced den-
sification [
15
,
16
] field-induced crystallographic defects nucleation, electric force interaction
with the chemical potentials [17,18] and electrochemical effects [19–21].
Flash Sintering has been applied to several ceramics with different electrical conduc-
tivities: semiconductors [
22
–
24
], electronic conductors [
25
,
26
], ionic conductors [
27
–
29
],
and composites [
30
–
33
]. Indeed, when considering good electric conductors, the flash
can be reproduced at low temperature (or even at room temperature) but it requires the
application of high electric current to induce sufficient Joule heating [
34
]. As a result,
Materials 2021, 14, 7655. https://doi.org/10.3390/ma14247655 https://www.mdpi.com/journal/materials
