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Creep of Polycrystalline Magnesium Aluminate Spinel Studied by an SPS Apparatus

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Creep of Polycrystalline Magnesium Aluminate Spinel Studied by an SPS Apparatus

Barak Ratzker et al. Materials (Basel).

Abstract

A spark plasma sintering (SPS) apparatus was used for the first time as an analytical testing tool for studying creep in ceramics at elevated temperatures. Compression creep experiments on a fine-grained (250 nm) polycrystalline magnesium aluminate spinel were successfully performed in the 1100-1200 °C temperature range, under an applied stress of 120-200 MPa. It was found that the stress exponent and activation energy depended on temperature and applied stress, respectively. The deformed samples were characterized by high resolution scanning electron microscope (HRSEM) and high resolution transmission electron microscope (HRTEM). The results indicate that the creep mechanism was related to grain boundary sliding, accommodated by dislocation slip and climb. The experimental results, extrapolated to higher temperatures and lower stresses, were in good agreement with data reported in the literature.

Keywords: SPS; creep; spinel.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Creep curves for spinel under pressures of 120–200 MPa in the 1100–1200 °C temperature range. The dashed lines indicate change of the slope.
Figure 2
Figure 2
Creep rates of spinel as a function of pressure, tested at various temperatures.
Figure 3
Figure 3
ln(strain rate) vs. ln(stress) for spinel tested under 120, 150 and 200 MPa.
Figure 4
Figure 4
Strain rate vs. the reciprocal of temperature.
Figure 5
Figure 5
Apparent activation energy as a function of stress.
Figure 6
Figure 6
Strain rate vs. applied stress. Extrapolation of our experimental data (dashed lines) and values reported in the literature for various creep conditions and grain sizes (indicated in the legend) are shown.
Figure 7
Figure 7
High resolution scanning electron microscope (HRSEM) images of the spinel samples: before creep (a); after creep at 1100–1200 °C (4% strain) under 120 (b); (7% strain) 150 (c) and (13% strain) 200 MPa (d). Compression direction is marked.
Figure 8
Figure 8
High resolution transmission electron microscope (HRTEM) images of spinel samples after deformation at 1100–1200 °C. Under 120 MPa (4% strain) triple-point voids and displaced triple points are shown (a); under 200 MPa (13% strain) grain separation and sliding along the grain boundaries (b) and dislocations (c) are shown. A weak-beam dark field (WBDF) image for g = 440 shows the high dislocation density within the grain after creep in response to 200 MPa pressure (d); The selected area diffraction pattern is presented in the insert (e). The examined cross-sections were perpendicular to the compression axis.

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