Metric and Topological Characterization of the Advanced Stages of Loose Stack Sintering

Abstract

A quantitative stereological study, including serial sectioning analysis, has been carried out to determine the topological and metric properties of the pore and grain boundary networks in a series of samples prepared by loose stack sintering a 5-μm nickel powder at 1250 °C. The evolution of the structure is found to be determined by an interplay between the rates of three proceses: channel closure in the pore network, annihilation of isolated pores, and grain boundary migration. For the conditions of this study, this interplay produced a path characterized by isolation of pores from the starting network; these pores effectively pinned moving grain boundaries, arresting grain growth. The isolated pores, thus pinned in grain boundaries, then disappeared, so that at the end of the sequence, only network porosity remained. The traditional view that holds that isolated porosity is stable is thus found to be naive; a valid description of the geometry of the porosity cannot be obtained unambiguously without serial sectioning analysis.