Corollary Spherical particles should not be cold pressed if they are to serve a structural function

Cold pressing of spherical powders does not result in significant mechanical bonding of particles and green strength is poor. With careful handling, cold pressing of spherical powder can be accomplished, followed by sintering to achieve particle bonding; P/M filters are an example.

Corollary: The particle surface quality directly effects the strength of the particle bond. Sintering is not effective in improving mechanical properties if particle surface contaminants such as carbides or oxides block diffusion of alloy species. Therefore, sintering requires clean surfaces or it must include a surface cleaning step such as deoxidation.

Corollary: The mode of densification affects the quality of the interparticle bonding. The strength of the bond between powder particles is improved by shear deformation in comparison to repressing or isostatic compaction. Shear plus pressure breaks up surface contaminants and promotes particle bonding. As surface cleanliness is improved toward being contaminant free, there is less difference between consolidation processes involving high or low amounts of shear.

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