Pressure assisted sintering stress exponent assessment methods: Accuracy analysis and effect of sintering stress

Abstract

Pressure assisted sintering models involve creep based mechanisms having different stress exponent values. The later evolve from linear viscous diffusional creep mechanisms to highly non-linear mechanisms involving dislocation motion. Consequently, the determination of the stress exponent is of key importance to define the sintering mechanisms and one of the first parameters to identify for the assessment of sintering model. Different methods exist in the literature involving tests at different pressures or with a stepwise pressure profile to extract the creep stress sensitivity. Open questions remain on the accuracy of these methods with the impact of sintering stress (high in ceramics nano-powders) or transient microstructure evolution for the stepwise approaches. This accuracy issue is investigated on an alumina submicronic powder by comparing different methods based on sinter-forging and Spark Plasma Sintering (SPS) at 1200 °C. We show that the sintering stress has a high influence on the identified value of stress exponent. Otherwise, the combination of sintering stress and transient behavior at the level of the pressure “jump” of the stepwise method can lead to high disturbance in the identified values.