Activation of the sintering of iron powder by nickel, cobalt, and manganese additions. I

Abstract

1. The extent of the influence of activating additions on the strength characteristics of metal powder compacts during solid-phase sintering is essentially governed by two factors, viz., the influence of the additions on the densification process during sintering and on the strength of the metallic base material. 2. In the presence of various activating metal additions, correlation is not always observed between the course of the densification process of compacts during sintering and the final mechanical properties of the compacts. The alloying of the contact zones between powder particles by atoms of the metal introduced brings about a strengthening of the material, but the shrinkage process under these conditions may be inhibited. Consequently, the selection of the type of addition must be governed by the specific property requirements of each part. 3. Of the nickel, cobalt, manganese, and iron additions investigated, nickel and manganese were found to exert the strongest influence on the strength the characteristics. In the case of nickel additions, sintering in the temperature range 900–1000°C is particularly effective. Because of the suppression by nickel of the deleterious effect ofα-γ transformation, the shear strength of specimens of about 25% porosity sintered under these conditions is 5–6 daN/mm2 higher than that of pure iron. On the other hand, manganese additions adversely affect properties during sintering in this temperature range, but substantially raise the strength at higher sintering temperatures (1100–1200°C). 4. The highest strength may be attained by introducing nickel and manganese by the method of deposition from nickel or manganese nitrate solutions with subsequent reduction annealing. Even higher properties after sintering in the range 950–1150°C are secured by ferromanganese additions.