Date of Award
Doctor of Philosophy
Materials Science and Engineering
Alan M. Russell
An Al-20vol.% Sn metal-metal composite was deformation processed by extrusion, swaging, and wire drawing to a total true strain of 7.4, resulting in a microstructure with Sn filaments in an Al matrix. Both the size and spacing of the Sn filaments decreased as deformation processing progressed. Immediately after deformation, the Sn second phase showed a convoluted, ribbon-shaped filamentary morphology, but the Sn filaments spheroidized during prolonged storage at room temperature. The driving force for spheroidization is chemical potential gradient due to curvature difference along Sn filaments. A critical wavelength of lambda crit = 2piR can be used to determine the spheroidization tendency of Sn cylinder. When lambda > 2piR, spheroidization is predicted to occur.;The strength of these composites increased exponentially with the reduction in spacing of the Sn filaments. The relationship between UTS and deformation true strain is UTS = 72.6 exp(0.20eta). A Hall-Petch relationship between strength and filament spacing has been observed. Strengthening results from the filaments acting as barriers for dislocation motion.;The primary shape instability modes are cylinderization of ribbons, boundary splitting, spheroidization of cylinders, and edge spheroidization of ribbons. The determining factors dictating which mechanism is active are grain boundary energy, interfacial energy, and ribbon cross section aspect ratio.;The fiber texture was determined by orientation imaging microscopy to be <100> for Al and <001> for Sn. The 290 MPa ultimate tensile strength of the composite was greater than the rule-of-mixtures prediction. Comparisons are made with Al-Nb, Al-Ti and Al-Mg deformation processed metal metal composites and to various strengthening models for metal-metal composites.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Xu, Kai, "Microstructure and strength of a deformation processed Al-20%Sn metal-metal composite " (2003). Retrospective Theses and Dissertations. 1476.