Abstract: The high velocity compaction process of Ti-6Al-4V powder is simulated by using two-dimensional multi-particle finite element method. The morphological features of pores among particles are quantitatively characterized. The change laws regarding the morphology and area filling of various typical pores during the compaction process are analyzed in detail. The powder densification mechanism is studied from the aspect of the evolution of microscale pores. The simulation results show that when the compaction pressure is lower than a critical value (about 1 500 MPa), pores are mainly filled by particle rearrangement and plastic deformation, so that the slope of the density-pressure curve is steep, and the green powder assembly is easily densified. Above that critical pressure, the slope of the density-pressure curve gradually decreases, and powder densification becomes difficult. Microscopically, at the stage of particle rearrangement and plastic deformation, there are many quadrilateral pores with large area-ratios and small compression angles, as well as pentagon pores with arched structures that are easily damaged. Since these pores can be transformed into other polygonal pores during compaction, they have high filling ratios, and play a major role in the early and middle densification stages. When the compaction pressure is higher than the critical value, most of the quadrilateral and pentagonal pores has been transformed into triangular shapes. Additionally, there are a small number of polygonal pores with special packing structure. These pores that are hard to be filled lead to the difficult densification in the later stage. The research results establish a qualitative relationship between the morphological evolution of different types of pores and the difficulty of powder densification, which would provide theoretical guidance for both the construction of the compaction constitutive equation and the optimization of the forming quality.

Key words: Ti-6Al-4V, high velocity compaction, powder densification, multi-particle finite element method, pore morphology