Recent Developments of High-Pressure Spark Plasma Sintering: An Overview of Current Applications, Challenges and Future Directions

Abstract

Spark plasma sintering (SPS), also called pulsed electric current sintering (PECS) or field-assisted sintering technique (FAST) is a technique for sintering powder under moderate uniaxial pressure (max. 0.15 GPa) and high temperature (up to 2500 °C). It has been widely used over the last few years as it can achieve full densification of ceramic or metal powders with lower sintering temperature and shorter processing time compared to conventional processes, opening up new possibilities for nanomaterials densification. More recently, new frontiers of opportunities are emerging by coupling SPS with high pressure (up to ~10 GPa). A vast exciting field of academic research is now using high-pressure SPS (HP-SPS) in order to play with various parameters of sintering, like grain growth, structural stability and chemical reactivity, allowing the full densification of metastable or hard-to-sinter materials. This review summarizes the various benefits of HP-SPS for the sintering of many classes of advanced functional materials. It presents the latest research findings on various HP-SPS technologies with particular emphasis on their associated metrologies and their main outstanding results obtained. Finally, in the last section, this review lists some perspectives regarding the current challenges and future directions in which the HP-SPS field may have great breakthroughs in the coming years.

Keywords: HP-SPS; high pressure; spark plasma sintering.

Figure 1

(a) Dependence of crystallite size on SPS with temperature and applied pressure for two different commercial powders of alumina (TM-alumina and AA-alumina) (from [26]). (b) Relationship between the pressure required and the dwell temperature (5 min) to obtain samples with a relative density of 95% in the case of nanometric zirconia (8% YO_1.5). The full circles correspond to the temperature of sintering and empty squares to the grain size obtained (from [25]).

Figure 2

X-ray diffraction patterns (CuKα) of SPS-processed silicon carbide at (a) 40 and (b) 80 MPa. The blue symbols represent the diffraction peaks of α-SiC and the red symbols the diffraction peaks of β-SiC [35].

Figure 3

Schematic of an SPS apparatus. (1) Graphite punches. (2) Cylindrical die (usually in graphite). (3) Graphite spacers. (4) Upper water-cooled steel cylinder. (5) Lower water-cooled steel cylinder. Adapted from [25,42].

Figure 4

Schematics of HP-SPS devices reaching 1 GPa on 5 mm (A) [25] and 10 mm (B) [50] diameter samples.

Figure 5

(A) Section view of the sample cell assembly between two WC anvils (B) The Paris–Edinburgh HP-SPS module mounted in the SPS-HPD 25 (FCT) chamber and (C) in the Dr. Sinter SPS 825 chamber, working up to 2 GPa. Experiments were performed in two different laboratories: MATEIS, Lyon (France) and IRCER, Limoges (France).

Figure 6

Calibrations of the Paris–Edinburgh HP-SPS cell: (A) Calibration curve of the pressure performed from in situ neutron diffraction of a NaCl sample using its equation of state. The orange area indicates the pressure range accessible with the Paris–Edinburgh module mounted on standard SPS equipment (maximum load 250 kN) (B) Calibration curve of the temperature, as a function of the average power of the pulsed current, performed by placing a K-type thermocouple in the center of an alumina sample.

Figure 7

(a) Schematic of cubic press assembly showing the six opposite WC anvils and the cube assembly in the middle; (b) Enlargement of the associated cubic reaction chamber. (1) WC anvils. (2) Cubic reaction chamber. (3) Gasket material. (4) “Synthetic gasket material”. (5) Steel electrode. (6) First metallic disk. (7) Baffle. (8) Second metallic disk. (9) Graphite heater. (10) Salt capsule. (11) Metallic capsule where the sample is placed. The red arrows indicate compression axes. Adapted from [22,54].

Figure 8

HP-SPS device at the Institute of Advanced Manufacturing Technology (at Krakow) in Poland. Cross section (a,c) and photography (b) of the high-pressure reaction chamber and HP-SPS device schematic, where: 1—ceramic gasket (outer part); 2—ceramic gasket (inner part); 3—ceramic disc; 4—sample; 5—graphite disc; 6—graphite tube; 7—thermocouple (used only for temperature calibration). Quasi-isostatic compression of the preliminary consolidated powders is achieved as a result of plastic deformation of the gasket material (8) between anvils (9); electrical heating during HP-SPS process is provided by transformer (10), together with inverter (11), thus providing 1 kHz direct pulsed current. Adapted from [57,58].

Figure 9

HP-SPS device at the Institute of Advanced Manufacturing Technology (at Krakow) in Poland (from [57]).

Figure 10

Microscopic images of the samples with 90 wt% diamond +10 wt% (Ti+ 2B). TEM image (a) and HREM image (b) of diamond composite sintered with classical HP–HT technique. TEM image (c) and HREM image (d) of diamond composite sintered with HP-SPS technique (from [58]).

Figure 11

(a) HP-SPS belt apparatus showing the high-pressure reaction chamber (in green), where the sample is located, and the external support (the “belt”), used to contain the pressure. (b). High-pressure reaction chamber: A: Fired pyrophyllite tube; B: Graphite heater; C: Molybdenum discs sandwiching mica ring; D: Steel cover filled with fired pyrophyllite pellet; E: Crude pyrophyllite gasket; F: Polymer gasket (adapted from [59]).

Figure 12

Density evolution with pressure in recovered α-Al₂O₃ ceramics sintered at 800 °C from γ-Al₂O₃ with nano or micro-sized grains. The first symbol at lowest pressure corresponding to conventional SPS (100 MPa). (Figure adapted from [61]).

Figure 13

An SPS apparatus commercialized by FUJI Electronic Industrial Co., Ltd. (Tsurugashima, Japan) (A) and the tabletop HP-SPS device (B).

Figure 14

SPS pulse pattern, with an On:Off setting of 12:2, delivered using the homemade pulse generator to the tabletop HP-SPS.

Figure 15

Sintering curve of an anatase-TiO₂ nanopowder recorded under 1 GPa upon heating up to 650 °C.

Figure 16

Sintering curve of a diamond nanopowder recorded under 5 GPa upon heating up to 1900 °C.

Figure 17

The compact very high-pressure SPS installed on PSICHÉ beamline at SOLEIL, French synchrotron. Scheme of the press set-up for collecting diffraction patterns—Details of the sample environment.

Figure 18

In situ X-ray diffractograms collected on heating during SPS treatment of a 15 nm TiO₂ nanopowder at 3.5 GPa (ID27 beamline, ESRF, λ = 0.2468 Å).

Figure 19

In situ X-ray diffractograms collected on heating (200 °C/min) during HP-SPS treatment of a diamond nanopowder (PSICHE beamline, SOLEIL, in energy dispersion at a fixed angle).

Figure 20

(a) DP-SPS configuration. 1. Graphite punch; 2. Silicon carbide space; 3. Tungsten carbide spacer; 4. Tungsten carbide punch; 5. Internal graphite die; 6. Graphite die. (b) Schematic of the sample being compressed by tungsten carbide punches inside the graphite die, during sintering. (c) Spark plasma texturing (SPT) configuration. 7. Pre-sintered sample; 8. Mold. Adapted from [90,91].

Figure 21

3D scheme and cross-section of the RoToPEc module which can be installed on HP-SPS device [52]: (1) rotating upper anvil, (2) rotating lower anvil, (3) lower gear reducer, (4) upper gear reducer, (5) upper thrust bearings, (6) lower thrust bearings.