Rheology and Kinetics of Pressure Sintering

Abstract

The rheological viscous flow model of deformable, irreversibly compressible, porous body based on mechanics of continua, and creep theory of crystalline materials, is used to describe quantitatively the sintering of powder materials with pressure in isothermal and nonisothermal conditions. Densification of the porous body occurs under action of Laplace pressure, generated by surface tension, and applied pressure. The densification kinetics of porous metals and crystalline compounds in initial and intermediate stages of sintering with static external pressure represent nonlinear steady-state creep controlled by a climb dislocation mechanism in solid matrix forming porous material. Activation energies of this mechanism are consistent with the bulk diffusion. A diffusional creep controls the pressure sintering kinetics in a later stage. The rheological models of deformable viscoelastic bodies and the associated dynamic strain theory for viscoelastic irreversibly compressible bodies, based on the energy conservation law, enable a quantitative description of their densification under dynamic loading. At the same time it is taking into account the internal energy of deformable body. The solutions of dynamic systems involve the mechanical interaction of compacting machine with this body. The simulation of impact sintering of porous metals shows that the viscosity of the matrix, that forms the porous body, and the activation energy of viscous deformation dramatically decrease with increasing initial impact velocity. This promotes the compaction of the material to practically nonporous state and enhances its mechanical properties.