Densification and Deformation Behavior of a Porous Metal Strip during Hot Rolling

Abstract

The relationships between the longitudinal and thickness strains and between the apparent plastic Poisson's ratio and the relative density achieved during hot rolling of porous nickel strips of initial relative densities 0.36, 0.48, and 0.67 are experimentally determined. The experimental data have been found to agree well with the results predicted from analytical relationships. Hot rolling of such porous metal strips can be divided into three distinct stages. In stage I, the powder particles rearrange and restack as the rolling progresses and the longitudinal elongation and apparent plastic Poisson's ratio are negligibly low. The end of this stage is marked by the situation when no further densification without longitudinal flow is possible by hot rolling. In the present case, stage I continues until a relative density of 0.7 has been achieved in the strip, resulting into a predominantly orthorhombic pattern of particle arrangement. Stage II,i.e., densification from the relative density from 0.70 to 0.95, is associated with the continuous increase in interparticle contact area, longitudinal elongation, and apparent plastic Poisson's ratio as the hot rolling progresses. In this stage, the interconnected porosity changes to the isolated one. In stage III,i.e., densification beyond the relative density of 0.95, pore fragmentation and collapsing of the opposite pore surfaces take place until all the porosity has been eliminated.