Investigation of the Sintering Process During Formation of Solid Solutions
The formation of nonideal solid solutions during sintering can influence the sintering process positively (by means of higher chemical diffusion) or negatively (by means of the Kirkendall effect). It remains to be established whether such results are also obtained in nearly ideal systems. Bodies of very fine (2–5 μ) cobalt- and nickel-powder mixtures over the whole concentration range, compacted at low and high pressures, were sintered at temperatures between 300 and 1100°C. Model experiments (Ni-rod with Ni-wire and intermediate Co-layers; Co-rod with Co-wire and intermediate Ni-layers) were also performed. Results- of the tests are as follows.
Bodies compacted at low pressure shrink more during the earlier stages of sintering and homogenization (low temperature) than do the individual components. At later stages, as well as with higher pressed compacts at all sintering stages, the bodies show less shrinkage than the individual metal powders.
Intermediate Ni-layers between Co-rod and Co-wire cause increasing neck growth; Co-layers between Ni-rod and Ni-wire cause the opposite effect. All results can be explained by diffusion and activities data. Diffusion coefficients are higher in Ni-rich alloys than in Co-rich ones.
The rapidly homogenizing mixtures of very fine powders react sensitively to small deviations from the behavior of an ideal mixture as well as the models with their point or line contacts. Normal chemical diffusion samples with plane contacts do not indicate such small effects.
KeywordsSolid Solution Sinter Behavior Chemical Diffusion Neck Width Excess Vacancy
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- 1.Eisenkolb, F., Fortschritte der Pulvermetallurgie, Vol. 1, F. Eisenkolb and F. Thümmler (eds.), Akademie-Verlag (Berlin), 1963, p. 425.Google Scholar
- 2.Thümmler, F., “Einfluß geringer mischkristallbildender Legierungsanteile auf das Sinterverhalten,” Planseeber. Pulvermet. 6: 2 (1958).Google Scholar
- 3.Brophy, J. H., L. A. Shepard, and F. Wulff, “The Nickel-Activated Sintering of Tungsten,” in: Powder Metallurgy, W. Leszynski (ed.), Interscience Publishers, Inc. (New York), 1961, p. 113.Google Scholar
- 4.Vacek, J., “Nove Poznatky o Slinovatelnosti,” Hutnicke Listy 10: 469 (1955).Google Scholar
- 5.De Dyk Man and A. N. Nesmeyanov, “Thermodynamic Investigation of Cobalt-Nickel Solid Solutions,” Izu. Akad. Nauk SSSR, Otd. Tekhn. Nauk, Met. i Toplivo (1960), p. 75.Google Scholar
- 7.Thümmler, F., “Auswertung und Erscheinungsbild von Sinterversuchen an Modellkörpern,” Wiss. Z. Tech. Hochsch. Dresden 4: 1045 (1954/55).Google Scholar
- 8.Seith, W., Diffusion in Metallen, Springer-Verlag (Berlin), 1955, p. 156.Google Scholar
- 9a.G. C. Kuczynski and P. F. Stablein, “Sintering in Multicomponent Systems,” International Symposium on Reactivity of Solids, Elsevier Publishing Co. (Amsterdam), 1961, p. 91.Google Scholar
- 10.Heumann, T., and A. Kottmann, “Über den Ablauf der Diffusionsvorgänge in Substitutionsmischkristallen,” Z. Metallk. 44: 139 (1953).Google Scholar