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. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

M.Sc. (Chemistry) / Please refer to full text to view abstract

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The elastic constants, phase stability, heat of formation and the Debye temperature of various noble metal compounds in the stoichiometry A3B (where A = Pt, Ir, Rh, Ru, Pd and B = Al, Hf, Zr, Sc) were studied using the ab initio Density Functional Theory - Projector Augmented Wave method. A total of 24 compositions was investigated, of which 16 compounds were predicted to be thermodynamically stable. The remaining eight compounds were found not energetically favorable, due to positive or low heats of formation. According to the Density of States studies, the L12 structure was predicted in 8 compounds while four compounds had the D024 structure. Among compounds with the L12 structure, the hardest phase predicted was L12-Ir3Hf. L12-Pd3Sc was predicted as the least hard and most ductile compound. In compounds with the D024 structure, Pt3Zr was predicted having highest hardness and highest melting point. In all the compounds, the strongest interaction was found between hafnium and the noble metals and least interaction was with aluminum. The melting points from ab initio and molecular dynamics calculations slightly over-predicted experimental values, but showed the same trends. Both the fracture toughnesses and the melting points deduced using the Sutton-Chen potentials had similar trends to ab initio results, suggesting that the Sutton-Chen potentials is adequate for simulating metallic phases.

Thesis (M.S. in mechanical engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Feb. 4, 2010). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 42-45).