March 6-11, 2016
Numerical modeling of sintering and its process variants (such as Hot Pressing, Hot Isostatic Pressing (HIP), Field Assisted Sintering Technique (FAST) or Spark Plasma Sintering (SPS), etc.) has been a field of interest among researchers and industrialists due to its efficiency in predicting various sintering characteristics such as densification, volumetric and shape changes. Thus, various mathematical models have been developed over the years, where, earlier models for sintering included rheological investigations which were able to capture the macroscopic shape and volume changes of a porous body over the process of sintering and were known as phenomenological models . Due to the limitation of their dependency on rheological parameters, physical based models [2, 3] were developed by considering the effects of various physical diffusion mechanisms on various sintering parameters such as grain size, neck size, sintering stresses and temperature. In this work an extension to the physical based model for FAST has been proposed and a numerical investigation has been carried out. Due to its excellent thermal and electrical properties a binderless hard metal, Tungsten Carbide (WC), has been chosen in this numerical study.
Various authors, simulated the FAST process with either coupled electrical-thermal simulations  or coupled electrical-thermal simulations with subsequent structural simulations with deformations in different steps. Here, a coupled structural-electrical-thermal Finite Element (FEM) simulation, in a single step, is carried out in ABAQUS/Standard. The physical model for solid state sintering considers various mass transport mechanisms such as grain boundary diffusion, surface diffusion and volume diffusion. In the case of FAST, the model is extended by considering an additional term in the calculation of normalized shear and bulk viscosities, to compensate for the mass transport due to the electrical effects. The passage of electrical current through the graphite dies and the WC powder component leads to generation of Joule heat. On heating, sintering parameters such as sintering stress, grain growth, etc. are calculated as solution defined variables for each integration point in the FEM Model. The rate of densification is calculated based on the modified physical based constitutive equation for FAST, proposed in this work. The material and model parameters have been derived from reliable literature sources with certain changes in some cases.
Model parameter based sensitivity analysis is carried out to study the influence of electrical parameters and also to validate the implementation technique. These numerical investigations help us to determine the electrical influences in the densification process for FAST. As further investigation, a systematic experimental study is proposed in order to validate the constitutive model proposed in this work.
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