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Date of Award
Campus Access Dissertation
Doctor of Philosophy in Materials Science and Engineering (PhD)
Administrative Home Department
Department of Materials Science and Engineering
Douglas J. Swenson
Committee Member 1
Timothy C. Eisele
Committee Member 2
Stephen A. Hackney
Committee Member 3
Paul G. Sanders
Gasars are directionally porous materials formed by the solidification of a gas-saturated melt. The pores are formed due to the change in gas solubility upon solidification of the melt. The porosity and pore size formed are affected by the direction and rate of solidification, soluble and inert gas partial pressures, and melt temperature. Gasars can be formed in many systems, including aluminum-hydrogen, copper-hydrogen, iron-nitrogen, magnesium-hydrogen, and nickel-hydrogen systems. Studies on gasar formation are largely qualitative, containing few if any sample replicates, and often lack quantification of key processing variables (such as solidification rate). This work was undertaken in an attempt to better understand the basic formation of gasars using the copper-hydrogen system at subatmospheric gas pressures (less than 91.2 kPa/0.9 atm). Samples were made using electrolytic copper which was saturated with hydrogen gas and tilt poured onto a water-cooled copper chill (in order to directionally solidify). For each set of processing conditions, three samples were cast. Solidification rate, porosity, pore size, and inter-pore spacing were measured for the samples. The solidification rate ranged from 1.0 to 4.1 mm/s depending on the sample diameter. Porosity was found to decrease with increasing solidification rate and experimental results and predicted porosities were in better agreement for samples with higher total applied pressure. Pore size was found to increase with decreasing solidification velocity, and the total applied pressure had the greatest effect on the pore size (with decreased pressure resulting in larger pores). Pore size distribution was found to be bimodal. Inter-pore spacing was found to increase with decreasing solidification rate and total applied pressure. Results were analyzed and compared with existing models (some of which were modified for use with the copper-hydrogen system) and comments on the effectiveness of the models are provided.
Rau, Helen J., "Formation of Copper Gasars at Subatmospheric Pressures", Campus Access Dissertation, Michigan Technological University, 2016.