Numerical simulation of solid-state sintering of metal powder compact dominated by grain boundary diffusion

by 1976- Zhang, Rui

iii The research effort is oriented towards the modeling of metal powder sintering to accurately predict the densification and distortion of a sintered part, which is mainly due to the differential shrinkage of a green compact. This research focuses on the study of the simulation of the sintering process that is dominated by grain boundary diffusion, which is recognized as one of the dominating sintering mechanisms. Specifically, a viscoelasticity model that accounts for the microstructural grain growth has been developed to simulate the thermal induced creep deformation in sintering. Sintering stress is treated as an equivalent hydrostatic pressure that links the microscale evolution to the macroscale deformation. To support that linkage, a grain boundary counting procedure has been modified to quantify the grain size distribution. The material resistance of viscous flow is included in the model as a thermally activated process using an Arrhenius-type temperature relation to represent the apparent viscosity. The finite element method is used to implement the simulation. Results of the compaction simulation such as shape change, residual stress and density distribution data are transferred into the sintering simulation as initial conditions. Since no extra heat source is generated during sintering, the thermal analysis is independent of the creep analysis so that an uncoupled heat transfer analysis yields time-dependent temperature fields that are used to drive the sintering simulation. The simulation is performed in ABAQUS, and an in-house FEM code (SinSolver) is used as a supporting tool and verification. iv Stainless steel 316L is chosen in this research due to its wide range of industrial applications and representative sintering mechanisms. Comparison and analysis on the simulation versus the dilatometry experiments of shrinkage are consistently close and improve the understanding of when and how the sintering mechanisms act in a sintering cycle.