Synergistic densification mechanism of irregular Ti powder during CIP: 3D MPFEM simulation with real-shape particles
Bao Wang, Kejia Pan, Shuai Gao, Shixing Wu, Chao Zhao, Xuan Luo, Qi Peng, Minghan Sun, Dongdong Li, Ning Li, Yuanyuan Li
Abstract
• An innovative 3D-MPFEM model incorporating realistic powder morphology, size distribution and stacking configurations is constructed. • The influence of contact forces ( F N ⇀ and f ⇀ ) on particle motion and associated densification is thoroughly investigated • The synergistic and complementary mechanism between the spheroidization of coarse powders and the flattening of fine powders in particle size matching is firstly elucidated. • The downsizing and homogenization of residual micropores are quantitatively analyzed, and a criterion for identifying suitable CIP pressures is proposed. Achieving high green density is essential for ensuring the mechanical properties of powder metallurgy workpieces. However, the densification behavior of irregular ductile powders remains unclear due to oversimplification in current numerical simulations. To address this, a three-dimensional multi-particle finite element method model incorporating realistic powder morphology, size distribution, and stacking structure is constructed. It is found that a pivotal motion-deformation synergistic stage exists between the conventional particle rearrangement and elastic–plastic deformation stages. In this stage, plastic deformation is driven by the spheroidization of coarse powders, whereas the resulting vacancies in the stacking structure facilitate slight particle motion. Thereafter, plastic deformation is dominated by the flattening of fine particles, and the pore-filling capacity decreases due to the reduction in non-contact surface area. This synergistic and complementary interaction between the spheroidization of coarse powders and the flattening of fine powders enhances mechanical interlocking and promotes micropore closure. As a result, the micropores exhibit a tendency of downsizing and homogenization, substantially boosting the potential for achieving full densification during sintering. Based on these findings, a method for determining the optimal forming pressure is proposed, considering the manufacturing costs of powder compacts and the characteristics of the micropores in both green and sintered bodies.