Influence of Electric Current on Efficiency of Field Assisted Consolidation of Powder Materials
Spark plasma sintering (SPS) has clear advantages of fast densification and lower grain growth compared with other powder consolidation techniques such as hot pressing (HP). Many researchers studied intrinsic electric current effects during the SPS process, yet the results of these studies are still controversial due to the complexity of the SPS technology.
In this study, we investigate various consolidation methods with and without electric current assistance to achieve the deconvolution of the electric current effects from the temperature effects. The spatial distribution of the electric current passing through the powder during SPS is modeled using the finite element method. The porosity-interparticle neck area geometrical relationship is utilized to estimate the electric current density inside the powder volume subjected to SPS. For the first time, by taking into account the explicit influence of the electric current effect on the SPS densification mechanisms, the governing equations describing hot pressing are modified to enable an SPS-specific constitutive analysis. The densification mechanisms of various ceramic (ZrN) and metallic (W and Mo) powders are determined by the inverse regression of the new SPS constitutive equations and by utilizing the experimental results on powder consolidation with and without the participation of the electric current effect.
We show that the electron backscatter diffraction (EBSD) technique can be a useful tool to demonstrate the densification mechanism of the powders during the sintering. The grain size and grain growth factors are incorporated into the sintering constitutive equation too to elucidate the grain growth effect on the material behavior governing parameters.
Additionally, the known but controversial intrinsic electric current effects such as surface cleaning and retardation of the grain growth are analyzed for the consolidation of the Mo nanopowders using SPS.
Finally, an energy efficient and fast consolidation technique utilizing the highly concentrated electric current flow through a conductive powder by manipulating the electric current trajectory is developed.