Effects of heating rate on densification and grain growth during field-assisted sintering of α-Al2O3 and MoSi2 powders

Two types of powders, electrically conductive MoSi2 and insulating alpha -Al2O3, were sintered by a field-assisted sintering technique (FAST) using heating rates from 50 degreesC to 700 degreesC/min. The Al2O3 powders were sintered to 99 pct density at 1100 degreesC for 2 minutes under 45 MPa pressure. For Al2O3, no exaggerated grain growth was observed and the final grain size inversely scaled with the heating rate. Such a grain growth behavior fits the literature models based on multiple transport mechanisms for constant-heating-rate sintering. The density reached by MoSi2 under similar sintering conditions was 91 pct. The grain size was independent of the heating-rate value. Specific electrical field and pressure effects are shown to contribute to enhanced densification and minimal coarsening in each material.