A SYSTEMATIC PROCEDURE TO STUDY HOT PRESSING AND SPARK PLASMA SINTERING KINETICS

A procedure for data collection and processing was developed to conduct accurate kinetic analysis in pressure assisted sintering techniques, such as hot pressing (HP) and spark plasma sintering (SPS). Densification of MgAl2O4 by SPS was chosen as a model system, where the kinetics were analyzed by utilizing the modified creep equation. Displacement data used in the equation was gathered by path measurement system (PMS) of the SPS equipment. Effects of temperature control accuracy, load cell accuracy and resolution of the PMS on the reliability of collected displacement data were evaluated. Dilution of the data in order to reduce the noise in strain rate values caused by the low resolution of the PMS system, which is only 10 μm, was observed to affect calculated stress exponents (n), significantly. Different n values in the range of 1.7-2.8 in a narrow interval of 83-86 % relative densities were found as a function of dilution degree. On the other hand, differentiating the strain with respect to the time interval of every single 10 μm displacement was shown to provide more consistent results. n values of ≈2.2 with a standard deviation of 0.15 were calculated for the same density intervals