Model experiment on the deformation behavior of porous sintered preforms

Abstract

To clarify the pore elimination processes in sintered preforms under static compressive stress, a model experiment is carried out.
Spherical copper particles with particle size between 10 and 12 mesh are sintered in a graphite mold at 1000°C for 1 hr. Sintered preforms with a relative density of 48% are then compressed in cylindrical dies at compacting pressures from 0.5 to 10 ton/cm² without any lubricant. Preform density after deformation is measured by means of size-weight measuring method and Archimedean method, and plotted against compacting pressure. Pore elimination due to deformation is examined by a scanning electron microscope.
The results obtained are summarized as follows:
1) Deforming process is separated into three characteristic stages. The transition from stage 1 to stage 2 occurs at the preform density of 74% theoretical, and the transition from stage 2 to stage 3 corresponds to the change from continuous to closed pore.
2) Plastic deformation occurs in all the three stages, in stage 1 transitional restacking takes place, in stage 2 local deformation at contacting regions and stage 3 overall deformation of the bulk material.
3) The volume of surface residual pore is about two-thirds of total pore volume.