Stresses Induced by Differential Sintering in Powder Compacts

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Abstract
Stresses created by differential sintering, due to differences in initial bulk density, were determined, to an order of magnitude, by an experiment which estimated the differential sintering phenomenon on a macroscopic level. The experiments entailed determining the shrinkage rates of a powder isostatically pressed to two bulk densities. Using this information, stresses were determined by forcing the slower‐densifying compact to shrink at the same rate as the faster‐densifying compact and measuring the resulting forces with a load cell. Maximum stresses (between 1 and 3 MPa) were observed to occur in the intermediate stage of densification. Despite larger differential strains at higher temperatures, stresses decreased to zero at the latter stage of densification. Viscoelastic experiments, of the stress‐relaxation type, were performed. Results showed that the sintering specimen was more rigid at lower temperatures and more fluidlike at higher temperatures. This explains the development of maximum stresses at intermediate temperatures.