The introduction of 0.5-1.0 wt.% graphite to the powders prepared by Self-propagating High-temperature Synthesis (SHS) is found to be highly beneficial for the removal of oxide impurities (from 2.7-8.8 wt.% to 0.2-0.5 wt.%) during spark plasma sintering (1950 degrees C/20 min, 20 MPa) of (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B-2 and (Hf0.2Mo0.2Ta0.2Zr0.2Ti0.2)B-2 ceramics. Concurrently, the consolidation level achieved is enhanced from about 92.5% and 88%, respectively, to values exceeding 97%. While a further increase of graphite slightly improves samples densification, final products become progressively richer of the unreacted carbon.It is assumed that graphite plays a double role during SPS, e.g. not only as a reactant during the carbothermal reduction of oxides contaminant, but also as lubricating agent for the powder particles. The latter phenomenon is likely the main responsible for the densification improvement when 3 wt.% or larger amounts of additive are used. Another positive effect is the crystallite size refinement of the high-entropy phases with the progressive abatement of oxides, to confirm that their presence promotes grain coarsening during the sintering process.

Barbarossa, S., Orrù, R., Garroni, S., Licheri, R., Cao, G. (2021). Ultra high temperature high-entropy borides: Effect of graphite addition on oxides removal and densification behaviour. CERAMICS INTERNATIONAL, 47(5), 6220-6231 [10.1016/j.ceramint.2020.10.200].

Ultra high temperature high-entropy borides: Effect of graphite addition on oxides removal and densification behaviour

Barbarossa, Simone
Primo
;
2021-01-01

Abstract

The introduction of 0.5-1.0 wt.% graphite to the powders prepared by Self-propagating High-temperature Synthesis (SHS) is found to be highly beneficial for the removal of oxide impurities (from 2.7-8.8 wt.% to 0.2-0.5 wt.%) during spark plasma sintering (1950 degrees C/20 min, 20 MPa) of (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B-2 and (Hf0.2Mo0.2Ta0.2Zr0.2Ti0.2)B-2 ceramics. Concurrently, the consolidation level achieved is enhanced from about 92.5% and 88%, respectively, to values exceeding 97%. While a further increase of graphite slightly improves samples densification, final products become progressively richer of the unreacted carbon.It is assumed that graphite plays a double role during SPS, e.g. not only as a reactant during the carbothermal reduction of oxides contaminant, but also as lubricating agent for the powder particles. The latter phenomenon is likely the main responsible for the densification improvement when 3 wt.% or larger amounts of additive are used. Another positive effect is the crystallite size refinement of the high-entropy phases with the progressive abatement of oxides, to confirm that their presence promotes grain coarsening during the sintering process.
2021
Settore FIS/01 - Fisica Sperimentale
Barbarossa, S., Orrù, R., Garroni, S., Licheri, R., Cao, G. (2021). Ultra high temperature high-entropy borides: Effect of graphite addition on oxides removal and densification behaviour. CERAMICS INTERNATIONAL, 47(5), 6220-6231 [10.1016/j.ceramint.2020.10.200].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10447/637013
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