Changes in the density and structure of multi-component materials containing copper, silver, and nickel, generated while sintering them
Stanisław Gacek Akademia Górniczo-Hutnicza, Wydział Metalurgii i Inżynierii Materiałowej, al. Mickiewicza 30, 30-059 Kraków
Annals 2 No. 5, 2002 pages 287-291
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abstract Products containing copper, silver, and nickel may be transformed into materials that unite favourable properties of their individual components. It is possible to form the structure and properties of sintered products provided that we profoundly understand the processes taking place whilst sintering a given group of materials, and that we are able to define how various factors influence the manufacturing process of a final product with a pre-determined chemical composition. In the paper, selected results of investigations on the density and structure of copper, silver, and nickel profiles while sintering them are presented. Mixtures of elementary powders were investigated. The chemical composition and characteristics of initial powders differed (Fig. 1). The profiles of a density of 70% were sintered at 750, 800 and 850oC, the sintering duration times were 15, 60 and 120 minutes. Whilst warming up and during the first phase of isothermal sintering, sinters swell. Thereafter, sinters shrink. The intensity of changes in density depends on the chemical composition and sintering conditions (Figs 2, 3). The structures of sinters investigated are highly differentiated with regard to the phase size and chemical composition of two- and three-component phases involved (Fig. 4). The kinetics of sintering multi-component materials depends on diffusion processes that take place during the sintering procedure. Upon sintering in the solid phase at 750oC, diffusion processes caused that twocomponent solutions of copper and silver, and of copper and nickel were produced (Fig. 5a-c). While sintering at 800 and 850oC, i.e. above the temperature of eutectic conversion, diffusion processes cause solid solutions to be manufactured, as well as to a liquid by-product. Within the structure of a three-component profile of copper, silver, and nickel, two structural components appear upon completion of sintering at t = 850oC. If the sintering duration is prolonged, grains expand (Fig. 5d-j).