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UBC Theses and Dissertations

Pore formation in metals Hirschfeld, Deidre Ann

Abstract

The formation of pores in castings is dependent on local solidification rates and the gas content in the liquid metal. Segregation of the gas in the interdendritic regions and the pressure drop due to solidification shrinkage contribute to the homogeneous nucleation of pores. Heterogeneous nuclei and other non-nucleating mechanisms are sufficient but not necessary for pore formation. These conclusions derive from experiments on pore formation in iron and aluminum. The formation of pores due to carbon monoxide in supercooled iron has been investigated as a function of the degree of supercooling and concentrations of carbon and oxygen in the melt. Pore formation in Al and Al + Cu alloys, due to hydrogen, has been investigated under a variety of solidification conditions. This includes directional solidification, directional casting, and casting into moulds at low and high temperatures. The size, distribution, and morphology of the pores has been measured as a function of hydrogen content and alloy composition, and related to the casting conditions. Experiments have also been conducted on Al containing Ag¹¹⁰ to investigate macrosegregation during directional solidification of Al alloys.

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