Graphite creep negation during flash spark plasma sintering under temperatures close to 2000$^\circ$C

TL;DR

This paper investigates graphite creep during flash spark plasma sintering at near 2000°C, modeling its onset and proposing process modifications to prevent deformation, enabling successful ultra-high temperature material sintering.

Contribution

It introduces a finite element model to determine graphite creep onset during FSPS and proposes process adjustments to avoid creep at high temperatures.

Findings

Graphite creep occurs above 2000°C at high pressures.

Modified FSPS process prevents graphite creep.

Achieved 95% dense silicon carbide in 30 seconds.

Abstract

Graphite creep has high importance for applications using high pressures (100 MPa) and temperatures close to 2000 {\textdegree}C. In particular, the new flash spark plasma sintering process (FSPS) is highly sensitive to graphite creep when applied to ultra-high temperature materials such as silicon carbide. In this flash process taking only a few seconds, the graphite tooling reaches temperatures higher than 2000 {\textdegree}C resulting in its irreversible deformation. The graphite tooling creep prevents the flash spark plasma sintering process from progressing further. In this study, a finite element model is used to determine FSPS tooling temperatures. In this context, we explore the graphite creep onset for temperatures above 2000 {\textdegree}C and for high pressures. Knowing the graphite high temperature limit, we modify the FSPS process so that the sintering occurs outside the graphite creep range of temperatures/pressures. 95 % dense silicon carbide compacts are obtained in about 30 s using the optimized FSPS.