The "Core-Shell" arch bridge effect: a new perspective on the CIP densification of Ti6Al4V blended elemental powders

Powder metallurgy, especially the blended elemental method, has garnered significant attention in titanium alloy manufacturing due to its cost efficiency and streamlined process. However, the impact of hard master alloy (MA) powders on inter-particle mechanical response, as well as the evolution and distribution of micropores, remains underexplored. To address this gap, Nano-CT experiments and Multi-Particle Finite Element Method (MPFEM) simulations are utilized to investigate the Cold Isostatic Pressing (CIP) behavior of Ti6Al4V mixed powders. It is found that residual porosity exhibits a non-uniform distribution, with larger pores preferentially located near the MA particles. This phenomenon is attributed to the "Core-Shell" arch bridge effect, wherein the robust support of rigid MA core, coupled with the force arch of surrounding soft Ti shell, forms a stable spatial arrangement and localized force chain network, significantly impeding pore closure. Fortunately, densification is enhanced by increasing the soft-to-hard particle size ratio (SR). While the close-packed configuration exhibits the most pronounced "Core-Shell" arching effect, the sub-close-packed structure demonstrates superior pore closure efficiency. Among various stacking arrangements, the triangular arrangement achieves the highest densification and minimal unloading rebound. Consequently, green density increases linearly with improved particle packing and stress distribution, driven by a higher SR. These insights support the design of an optimized Ti-MA mixed system, leading to substantial enhancement in the mechanical properties of both green and sintered bodies. • Overall homogenization and local non-uniform distribution of micropores are found. • The "Core-Shell" arch bridge effect hindering densification is first proposed. • Promoting densification by adjusting soft-to-hard particle size ratio is studied. • An optimized Ti-MA system with enhanced powder metallurgy properties is developed.