Effective Thermal and Electrical Conductivities of AgSnO 2 During Sintering. Part II: Constitutive Modeling and Numerica
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L simulation of resistance sintering (RS) is of great interest for a better understanding of the involved physical phenomena, and can be used as a support for optimizing the thermal cycle and the component geometry (punches, die, sample).[1–8] Moreover, the RS model requires valid constitutive equations to be able to calculate correctly the evolutions of the main properties of the granular media (density, effective electrical and thermal conductivities) during the whole process time. As presented in Part I, experimental evolutions of electrical and thermal conductivities of AgSnO2 depend strongly on the microstructural transformations, which take place during sintering. Two main mechanisms, plastic or viscoplastic deformation of particles under the effect of the load, and bonding
ELODIE BRISSON, Postdoctoral Student, HENRI DESPLATS, PATRICK CARRE, and PHILIPPE ROGEON, Doctor Lecturers, and VINCENT KERYVIN, Professor, are with the Laboratory IRDL FRE CNRS 3744, University of South Brittany, 56321 Lorient, France. Contact e-mail: [email protected] ERIC FEULVARCH, Doctor Lecturer, is with the University of Lyon, ENISE, UMR 5513, LTDS, 58 rue Jean Parot, 42023 Saint-Etienne Cedex 2, France. ALEXANDRE BONHOMME, Doctor-Engineer, is with the Schneider Electric Electropole, 31 rue Pierre Mendes France, 38050 Grenoble Cedex 9, France. Manuscript submitted February 28, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
diffusion between particles under the effect of temperature, change the contact conditions between the particles. Deformation changes, at a macroscopic scale, the apparent contact area, while bonding diffusion tends to eliminate the electrical and thermal contact resistances between the particles. The decrease of these contact resistances is due to the formation, growth, and coalescence of microscopic necks surrounding the micro-contacts between the asperities of the rough surfaces of the particles in contact. The microstructural modifications, and related mechanisms during the different sintering processes (FS, HP, or RS), represent a topic well described in References 9 through 11, for instance. During FS different diffusional mechanisms modify the microstructure. In the first stage of the process at temperatures lower than the densification threshold, surface diffusion and gas transport contribute to the growth of the necks while the relative density remains unchanged; only the contact conditions between the particles are improved. In the second stage, at temperature higher than the densification threshold, grain boundary and lattice diffusions can transport matter from the grain boundary (Coble creep) and from dislocations (Nabarro–Herring creep) within the particles to the periphery of the necks. Both neck size and relative density are enhanced in this case.[9–15] Two different types of models, microscopic and macroscopic, have been developed to calculate the evolution of the relative density.[9–11] Concerning the microscopic
approach, different equations are summarized in Reference 9 depending on various mecha
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