Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 1, 2009) Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [128]-134).

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 44)

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2007 Mar 24

Friction Stir Welding (FSW) is a solid state welding process invented and patented by The Welding Institute (TWI) in 1991, for joining ferrous and non-ferrous materials1. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joining dissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. This research work through material characterisation of the welded joints establishes a process window for the Friction Stir welding of 5754 Aluminium Alloy and C11000 Copper. Furthermore, preliminary studies83,85 on the FSW of aluminium and copper have revealed the presence of intermetallic compounds which are detrimental to the weld qualities. This research work is also aimed at establishing process parameters that will result in limited or no intermetallic formation in the weld. The joint integrity of the resulting welds will also be correlated with the input process parameters. Based on the preliminary investigations conducted, a final weld matrix consisting of twenty seven welds was produced by varying the rotational speed between 600 and 1200 rpm, and the feed rate between 50 and 300 mm/min using three different shoulder diameter tools – 15, 18 and 25 mm to compare the heat input into the welds and to achieve the best results. The welds were characterised through microstructural evaluation, tensile testing, microhardness profiling, X-Ray Diffraction analysis, electrical resistivity and statistical analysis – in order to establish the interrelationship between the process parameters and the weld qualities. viii Microstructural evaluation of the weld samples revealed that the interfacial regions are characterised by mixture layers of aluminium and copper; while 33 percent of the tensile samples are within the acceptable range (> 75 percent joint efficiency). High Vickers microhardness values were measured at the joint interfaces, which corresponded with the intermetallic compounds. The Energy Dispersive Spectroscopy analysis revealed the presence of thin layers of intermetallics in nanoscale at the interfacial regions. The diffractograms of the X-Ray Diffraction analysis showed small peaks for intermetallics in some of the welds. Low electrical resistivities were measured at the joint interfaces. The statistical analysis showed that the downward vertical force, (Fz) can significantly influence the resulting weld qualities. An overall summary of the analysis of the weld qualities - with respect to the shoulder diameter tools employed showed that the 18 mm shoulder diameter tool is most appropriate among the three shoulder diameters considered, and a process window of medium spindle speed of 950 rpm and low-to-medium feed rate between 50 and 150 mm/min is established for FSW of Aluminium and Copper. Welds produced at 1200 rpm and 300 mm/min with low heat input did not have intermetallics formed at the joint interface.

A study has been made of the elasticity associated with the martensite transformation in the polycrystalline β-phase alloy of composition Cu-33.6 wt. % Zn-4 wt. % Sn tested at room temperature. The mechanical properties of the material undergoing the stress induced martensite transformation have been examined. These properties are influenced by the elastic anisotropy of the bcc β-phase, the development, preferential distribution and morphology and the mechanical properties of the transformation product. The elastic shape change associated with the elastically accommodated, stress-induced martensitic transformation was always found to be accompanied by some plastic deformation. A relationship between the β-grain size, the sample thickness and the deformation response was observed. Specimens with grains extending through the sample thickness exhibited large reversible strains (∼2.5%), whereas specimens with a much smaller grain size/thickness ratio (<1) exhibited only limited transformation elasticity. The morphology of the thermal martensite and the Ms temperature was also found to be influenced by the ratio grain size/thickness (g.s./t). A lower Ms temperature was associated with a decreasing g.s./t ratio; only self-accommodating burst martensite was observed in very fine grained material. The Af temperature increased with a decreasing g.s./t ratio. Repeated loading (cycling) reduced the hysteresis of the stress strain curve for all g.s./t ratios tested, but was always accompanied by plastic deformation of the matrix and the development of non-reversible deformation martensite. The experimentally determined habit plane for the thermal and the stress induced martensite were in moderate agreement with the planes predicted by the phenomenological martensite theory (W.L.R.) assuming a {110} <1Ī0> microscopic shear. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Master of Science