A PHASE-FIELD MODEL WITH MECHANICAL PLASTICITY TO SIMULATE THE HOT-PRESS SINTERING OF ZINC SULFIDE

Infrared (IR) window and dome materials are used in defense and a variety of industries and have a unique set of material properties capable of surviving strenuous environments. IR window and dome materials must undergo rigorous design and testing to understand their thermal, structural, and optical limitations. In addition, manufacturing IR window materials is time-consuming, expensive, and requires substantial resources.

The objective of this research is to develop a model that predicts the final microstructure of powder Zinc Sulfide (ZnS), a material used in IR windows, during the hot-press sintering process. A phase-field model is presented with mechanical plasticity to simulate the hot-press sintering process. The phase field, representing individual particles, tracks grain size evolution and is coupled to the mechanical response. A parametric study is performed, to understand the effects of individual variables on material attributes, such as density, grain size, and porosity during sintering. The proposed model predicts the resultant sintered material, which can be used during product design and prior to manufacturing and testing. This will provide government and industry an opportunity to reduce resources required for product development.

The proposed phase-field model shows good comparison with published literature. A pore-controlled parametric study is conducted, showing that grain growth rate is controlled using pore volume fraction, pore to grain boundary area ratio, and mobility ratio. Simulations are performed with and without pressure, showing that grain growth rate is higher with no pressure and that microstructures approach equilibrium sooner with pressure. Results show that pore behavior is not predictable and that densification is driven by compression and not void movement.