The effect of small additions of disperse alumina inclusions on some characteristics of sintered nickel

Summary

Materials containing 0.5, 1, 2, 3, 4, and 5 vol. % Al₂O₃ were obtained from mixtures of nickel oxide and alumina powder reduced with hydrogen. The apparent density of the reduced powder and the relative density of pressed compacts vary nonuniformly with increasing alumina content. The material with 1 vol. % Al₂O₃ has the maximum values of these characteristics. The sintering shrinkage and relative density of sintered specimens are minima for this composition. Disperse alumina inclusions appear to exert a dual effect on the shrinkage of contacts during sintering: On the one hand, they decrease shrinkage by disturbing contact between the nickel particles; on the other hand, they facilitate the evacuation of the water vapor forming during sintering. The disperse inclusions break up the nickel submicrograins and affect the microdistortions of the nickel lattice.