Fractographic Analysis of Green Compacts of Metal Powders

Abstract

The paper examines the mechanisms that ensure the strength of green compacts prepared and tested in different thermal conditions (different homological temperatures of material made of Sn, Zn, Cu, Ni, and Mo powder particles compacted and tested in normal conditions). The role of powder particle shape is shown in simultaneous analysis of particle shape and fracture patterns of compacts using scanning electron microscopy. It is established that partial plastic fracture is found only in the Sn powder sample. When plastic powders with irregular branched particles (Cu, Ni) are compacted, the mechanism of adjusting particle surfaces to one another prevails and leads to all three components of mechanical interaction: interlocking, tangling, and jamming. When plastic powders with spherical particles are compacted, deformation of particles prevails. The ratio of the tensile strength of compacts (σ_в.н) determined with indirect method to the tensile strength of particle material (σ_в) shows a semilogarithmic dependence on the ratio of compacting pressure (Р) to the yield stress (σ_0,2) of the particle material. The dependence of the ratio of σ_в.н to the modulus of normal elasticity on the homological temperature of compacting and testing is divided into two linear dependences for spherical and nonspherical particles.