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Can the porosity be reduced by adjusting the grain size?

The porosity in high-temperature titanium alloy foil can indeed be reduced to a certain extent by adjusting the grain size. The specific reasons and mechanisms are as follows:
The effect of grain size on porosity
1. Fine grain strengthening effect
The fine grain structure can improve the plastic deformation ability and toughness of the material, so that the material can disperse stress more evenly during hot working and service, and reduce the formation of holes and cracks caused by local stress concentration.
2. Promote gas diffusion and discharge
The fine grain structure has more grain boundaries. As diffusion channels, the grain boundaries are conducive to the diffusion and escape of gas elements (such as hydrogen, oxygen, nitrogen, etc.) during hot working, thereby reducing the risk of gas gathering inside the material to form holes. 3. Inhibit hole expansion
Small and uniform grains can hinder the expansion and connection of holes, reduce the size and number of holes, and improve the density and mechanical properties of the material. 4. Improve the uniformity of the organization
Fine grains help to form a uniform organizational structure and avoid local defects and holes caused by coarse and uneven organization.
Implementation method
• Grain refinement is achieved by controlling hot working process parameters (such as temperature, deformation rate, cooling rate).
• Add trace alloying elements (such as B, Si, Zr, etc.) to promote grain refinement.
• Use multiple thermomechanical treatments and appropriate heat treatment processes to optimize grain size and distribution.
Precautions
• Too fine grains may lead to a decrease in the high-temperature creep performance of the material, so a balance needs to be struck between grain refinement and maintaining high-temperature performance.
• Fine grain strengthening should be combined with other process optimizations (such as purification, heat treatment, surface strengthening) to significantly reduce the porosity.
Summary: Adjusting the grain size, especially achieving fine grain structure, is one of the important means to reduce the porosity of high-temperature titanium alloy foil. Fine grain strengthening and promoting gas diffusion can effectively reduce the formation and expansion of pores, improve the density and mechanical properties of the material, but it needs to be combined with other process parameters for comprehensive optimization to ensure that the overall performance of the material meets the requirements of high-temperature applications.