Analytical models for initial and intermediate stages of sintering of additively manufactured stainless steel

In isotropic pressure-less sintering continuum mechanics models, densification kinetics is driven by the balance between the effective sintering stress and bulk viscosity. In components manufactured by binder jetting (BJ), the green structure created by the arrangement of spherical powder particles during printing is characterized by its high porosity (40–50%). This leads to a wide porosity range for the initial and intermediate sintering stages, where a complex combination of diffusion mechanisms drives matter redistribution through the porous compact. In this paper, a comprehensive analysis of the porosity effect on the resistance to densification of 316L BJ during sintering was performed by avoiding other highly influencing factors like δ-ferrite phase transformation. Different normalized bulk moduli expressions, inspired by Skorohod, Hsueh, and Abouaf sintering models, are used in the framework of the continuum theory of sintering. A new material constants determination algorithm based on the sintering experiments design and non-linear analysis of the model was proposed. This evidenced the critical importance of the experimental data collection for the determination of the required sintering model constants. Accordingly, material shear viscosity and normalized bulk viscosity constants were successfully determined based on dilatometry and grain size experimental data. The bulk moduli proposed comprise physical parameters which depend on the interparticle stress distribution or the initial high reactivity of the BJ compacts. The variation of powder size distribution and/or arrangement would potentially impact the determination of these constants in the normalized bulk moduli.