metallic porous structure formation via high speed collision

What is it about?

A new type of porous architecture is produced by high speed collision exhibiting an unusual feature of a porous template that consists of a hierarchical porosity made of nearly spherical pores. Dimensional analysis reveals that the porous structure has high porosity of 66% in the cross-section area, membrane structure including ultra-thin wall of 50 nm, and micron sized porosity including a significant proportion of sub-micron pores. The pores appear within a solidified structure where random nucleation of cavities occur. The spherical shape and the hierarchical organization of the porosity suggest a mechanism during the development of pores due to a cavitation phenomenon. Based on the thermodynamic considerations combined with computational simulation of the high strain rate collision, pores nucleation, growth and coalescence are explained as an ultra-fast isothermal and isochoric transition of a molten phase into a vapor phase. During these phenomena, cavities emerge due to a high rate of depressurization followed by a solidification at rapid cooling rate to produce the porous structure. An experimental comparison between cavitation onset and a fully developed cavitation allows to corelate the degree of cavitation with the depressurization intensity. The highly developed porous structure is favoured by the conditions corresponding to strong collision, i.e. high impact pressure followed by a significant depressurization. Together, those fast-dynamic phenomena represent a potential method for the manufacturing porous structures based on a micro-cavitation mechanism.

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Why is it important?

The increasing demand for the porous materials requires innovative methods to manufacture the porous structure. Recently, it was found that a ballistic collision enables a cavitation phenomenon that can produce a micro/nano-porous metallic structure . Thus, this work focusses to explore the detail of the porous structure formation, at an interface of a high-speed impact (HSI) welded joint. It is identified that HIS process enables to produce high porosity with thin membrane wall pours structure at an Al/Al welded interface.