Teruhisa Watanabe: Mechanism of Pore-Formation during Sintering of Self Lubricating Fe-Cu Bearing

At temperatures over the aFe-yFe transformation point (910°C), the inherent pores in the compact grow slightly because of the partial shrinkage accompanying the phase change of iron powders. Over the melting point of copper (1083°C), the copper powders melt and spread into the inherent pores, leaving the new pores, "copper-off pores", at the site of the copper powders by the same mechanism of porc-fomation as the "tin-off pores" on Cu-Sn compact®. The shapes of these new pores are similar to those of the copper powders and their sizes increase to slightly larger than those of the copper powders by corrosive action of molten copper to iron powders. At the same time the copper powders melt spread in the inherent pores also enlarges the latter by the corrosive action. Finally, the inherent pores and the new pores grow still more as a results of expansion of the compact following the alloying of iron and copper, and the sintered Fe-Cu compact holds numbers of pore necessary for a better self-lubricating action. When the samples are kept at the final temperature for a long time, all the pores formed begin to shrink as a result of densification of the sintered Fe-Cu compact. © 2019 Journal of the Japan Society of Powder and Powder Metallurgy. All rights reserved.