9705849 Zhang The project investigates an important process in materials science, solid state sintering of powders. In order to understand, control and predict the results of a sintering process, a close study of the process from a microstructural point of view is required. This project aims at process simulations based on specific sintering and related mechanisms rather than empirical, statistical functions. To model sintering from the mechanism point of view, the investigators employ a combination of experiments, mathematical models, and numerical simulations. Among many sintering mechanisms, the investigators have selected a common one which often dominates the sintering process, grain boundary diffusion. They couple mass transport by surface and grain boundary diffusion to form a complete mathematical system. This system involves high order nonlinear partial differential equations (PDEs) and moving boundaries. To solve this system, the investigators use an accurate and efficient numerical method for solving PDEs, combined with domain decomposition and adaptive/moving grids. A parallel computation in the simulation algorithm for both fine and coarse granularity level is also explored. To verify and corroborate the simulation, the project designs and carries out eight experiments. Seven of these target simple regular geometries of particles. For experimental reasons, Ni-coated W wires are used in most of the experiments. These experiments provide sound comparisons with the mathematical models based on individual mechanisms. The experimental results will be compared with the numerical simulations. These comparisons will verify and estimate the validity of the theoretical models. After comparisons based on these simple cases, the investigators will conduct an experiment on the sintering of an irregular cluster of particles where several mechanisms are involved and coupled. This experimental result will be compared with the numerical simulation of the enlarged complete mathematical system. %%% This investigation provides a powerful tool for studying the effects of sintering on the evolution of the microstructure of a sintering material. By combining experiments, mathematical models and computer simulations, the results will closely follow real world situations and better explain the microstructural evolution during sintering. The simulation will help scientists and engineers to understand better the properties of the sintered materials and to optimize sintering process. ***
