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

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The thermodynamic properties of the copper-manganese system were determined by the measurement of the vapour pressure of manganese tagged with Mn⁵⁴, using the Knudsen effusion method. Manganese shows a positive deviation from Raoult's law over the entire composition range. Copper, although showing a strong positive departure from Raoult's law at low copper content, shows a slight negative departure in copper-rich compositions. The negative departure, which can be associated with an affinity of copper for manganese is greatest at compositions of about 35% manganese. The behavior of both copper and manganese is much more ideal at lower manganese compositions. The ideal behaviour of the manganese in the alloys of low manganese content and the affinity of copper for manganese at about 35% manganese appear to corroborate Myers interpretation of the electronic configurations of copper and manganese in this system. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Zinc-titanium alloys (0.07-0.6 wt.%Ti.) in the form of compacted powder and chill castings have been extruded at temperatures between 150°C and 350°C. The mechanical properties of these alloys have been studied as a function of temperature, strain rate, grain size and intermetallic (Zn₁₅Ti) distribution. Due to a high value of "k" in the Hall-Petch relationship, maximum strengthening is obtained by a reduction in grain size. However because of an increasing amount of grain boundary shear, this potential is not realized. The operation of dynamic recovery mechanisms at 20°C and higher also results in limitations upon the development of high strength. The use of powder metallurgical techniques gives rise to the formation of intermetallic distributions which inhibit these processes and results in high strength (>60,000 p.s.i.) and low strain rate sensitivity (m ∼ 0.02). The mechanical properties are not a function of initial powder size. The properties obtained using chill castings do not reach these levels due to the difficulty associated with forming a fine second phase on solidification. Such a distribution is required to obtain a small stable grain size during subsequent extrusion. To satisfy compatibility requirements deformation modes other than the two supplied by basal slip must be invoked. High strengths are observed when grain boundary shear and migration are inhibited by the distribution of the second phase or by orientation effects. Under such conditions, non basal slip and basal slip are the operative deformation mechanisms. Significantly lower strengths result if grain boundary shear and basal slip satisfy the conditions necessary for ductile behaviour. The strain rate sensitivity parameter at 20°C lies in the range 0.02-0.07. Varying amounts of grain boundary shear occur, nevertheless deformation is slip controlled. Increased strain rate sensitivities are observed at high temperatures, but failure by cavitation limits ductility. The strain rate sensitivity is not a function of titanium concentration. Under constant fabrication conditions the strength generally increases with increased Zn₁₅Ti content. The thermal stability of the intermetallic distribution prescribes the fabrication conditions which must be used to develop high strength, and the temperature to which the mechanical properties can be retained. The high strength microstructures appear to be stable up to at least 150°C for short periods of time. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

The dissolution rates of niobium and zirconium cylinders in liquid steel have been measured in a 'dynamic way', with the help of a data acquisition and process control facility. Two distinct periods were identified; the steel shell period and the free dissolution period. / Lower bath superheats allowed a reaction to take place at the steel shell/niobium interface while higher superheats didn't; the intermetallic compounds Fe$ sb 2$Nb and Fe$ sb 2$Nb$ sb 3$ were identified as the reaction products. Niobium dissolved relatively slowly in liquid steel and its dissolution speed was increased under dynamic conditions (i.e., inductively stirred baths). / In the case of zirconium, an exothermic reaction occurred at the steel shell/zirconium interface and the intermetallics Fe$ sb 2$Zr and FeZr$ sb 2$ were identified as the reaction products. This reaction was triggered at 1220 K by the formation of a liquid Fe-Zr (76 at% Zr) eutectic. For the experimental conditions under which this study was performed, the hydrodynamic conditions of the steel baths did not seem to influence the dissolution rates of zirconium. / A simplified mathematical model was used in order to simulate the coupled heat and mass transfer phenomena which take place during the two periods.

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Thesis (Ph. D.)--Lehigh University, 2004. / Includes vita. Includes bibliographical references (leaves 168-172).

Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Bibliography: leaves 133-144.