Non—Isothermal Shrinkage of Compacts

On the basis of measurements of shrinkage, shrinkage rate, and defect density (determined by the method of mean positron lifetime) made on nickel and copper powder compacts, mechanisms are proposed to account for the intensive shrinkage observed during the non-isothermal sintering period when the compact is being heated to the isothermal sintering temperature. The influence of various process parameters is discussed. The unusually rapid material transport observed during both continuous and stepped heating is explained in terms of particle rearrangement and dislocation creep of material in the particle contact zones. Both processes are based on the conversion of specific vacancy configurations into dislocations that can move by climb. Their relative contributions to the overall shrinkage depend on the sintering and other process conditions obtaining. PMj0532