Development of master sintering curve for field-assisted sintering of HfB2-20SiC

Field assisted sintering (FAST) or spark plasma sintering (SPS) has emerged as a promising technology for densification of ultra high temperature ceramics like HfB2-20SiC at relatively low temperatures and shorter times. In the present study the concepts of master sintering curve (MSC) was applied to model the densification behavior of HfB92-20SiC during FAST process. An activation energy of 300 kJ/mol was estimated for field assisted sintering of HfB92-20SiC. The densification curves at various heating rates merged for activation energy of 300 kJ/mol confirming the applicability of MSC concepts to FAST process. The developed master sintering curves can be used to design sintering cycles and predict the densification of HfB92-20SiC during FAST process. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.X1188sciescopu

Sintering Behavior of Nanocrystalline Silicon Carbide Using a Plasma Pressure Compaction System: Master Sintering Curve Analysis

Nanostructured ceramics offer significant improvements in properties over corresponding materials with larger grain sizes on the order of tens to hundreds of micrometers. Silicon carbide (SiC) samples with grain sizes on the order of 100 nm can result in improved strength, chemical resistance, thermal stability, and tailored electrical resistivity. In this study, nanocrystalline SiC was processed in a plasma pressure compaction ((PC)-C-2) system at a temperature of 1973 K (1700 A degrees C) that was much lower than the temperatures reported for other sintering techniques. Microstructure of the resulting samples was studied and the hardness and the fracture toughness were measured. The grain sizes were on the order of 700 nm, the hardness between 22 and 24 GPa, and the toughness between 5 and 6.5 MPa center dot m(1/2). The master sintering curve (MSC) analysis was used to model the densification behavior of SiC powder sintered by the (PC)-C-2 method. The apparent activation energies for three different pressures of 10, 30, and 50 MPa were obtained to be 1666, 1034, and 1162 kJ/mol, respectively. Although densification occurs via diffusion, the activation energies were higher than those associated with self-diffusion in SiC (between 570 and 920 kJ/mol). A validation study of the MSC was also conducted and the variation in observed density from the density predicted by the MSC was found to range from 1 to 10 pct.open111010sciescopu

Design of Experiment Approach for Sintering Study of Nanocrystalline SiC Fabricated Using Plasma Pressure Compaction

Plasma pressure compaction (P(2)C) is a novel sintering technique that enables the consolidation of silicon carbide with a nanoscale microstructure at a relatively low temperature. To achieve a high final density with optimized mechanical properties, the effects of various sintering factors pertaining to the temperature-time profile and pressure were characterized. This paper reports a design of experiment approach used to optimize the processing for a 100 nm SiC powder focused on four sintering factors: temperature, time, pressure, and heating rate. Response variables included the density and mechanical properties. A L(9) orthogonal array approach that includes the signal-to-noise (SIX) ratio and analysis of variance (ANOVA) was employed to optimize the processing factors. All of the sintering factors have significant effect on the density and mechanical properties. A final density of 98.1% was achieved with a temperature of 1600 degrees C, hold time of 30 min, pressure of 50 MPa, and heating rate of 100 degrees C/min. The hardness reached 18.4 GPa with a fracture toughness of 4.6 MPa root m, and these are comparable to reports from prior studies using higher consolidation temperatures.open1199sciescopu