SINTERING SIMULATION OF STAINLESS STEEL POWDER COMPACTS

Summary Die compaction of powder metals is a classic discrete component fabrication process that relies on the rearrangement, distortion, and flow of metal particles in a die cavity, where the powders are compressed into a preform that is subsequently sintered. The sintered material has competitive properties, but without the cost associated with additional machining. One of the technological challenges when fabricating parts via powder processing methods is the ability to achieve undistorted, full density parts. For example, density gradients induced from the press motions lead to nonuniform shrinkage during the thermal processing. This research presents a model that predicts the shrinkage during high temperature sintering for powder compacts that have density gradients. The one-dimensional diffusional flow model for pressureless sintering includes an Arrhenius-type viscosity model and allows for the inclusion of grain growth and thermal expansion as functions of temperature. OVERVIEW OF PAPER The sintering simulation of metal powder compacts has been a popular topic in powder metallurgy processing for decades. This paper presents a phenomenological model of sintering which has been established to achieve the accurate prediction of sintering shrinkage throughout the sintering cycles. The sintering simulation results are compared and verified using the shrinkage data collected throughout a typical sintering cycle for a stainless steel 316 L cylindrical compact. SINTERING MODEL DESCRIPTION Because of the temperature and density variation during sintering, a thermal-visco-elasticity constitutive law has been employed in this model. The strain is comprised of the elastic strain eε, thermal strain tε, and creep strain crε. The portion of elastic strain is assumed to be linear and isotropic. The thermal strain is caused by thermal expansion or shrinkage. The incremental creep strain obeys a linear-viscous law as shown in Riedel (1990) and has the following form, () t