An electron microscopy study of tweed microstructures and premartensitic effects in high damping 53Cu45Mn2A1 alloy

• Main Author: Mayes, Larry Leroy.
• Other Authors: Perkins, Jeffrey Arthur
• Language: en_US
• Published: Monterey, California. Naval Postgraduate School 2012
• Online Access: http://hdl.handle.net/10945/23205

The evolution of tweed microstructure upon aging a 53Cu45Mn2Al alloy was studied in the transmission electron microscope (TEM). Characteristic (110) tweed contrast develops after the alloy is aged for 4 hours or longer at 400 C, which apparently is just within the miscibility gap, and is then cooled to room temperature. The microstructure evolved is proposed to consist of a small proportion of Mn-rich regions in a Cu-rich matrix. As the phase separation proceeds, the Neel temperature and the FCC-to-FCT transition temperature both rise within these Mn-rich domains, and as a result they begin to display incipient lattice instabilities when observed at room temperature. This takes the form of a 'flickering' effect in the TEM image. The flickering consists of consistent and repetitive contrast variations at specific locations in the microstructure. The significance of these microstructural features to damping is discussed. Keywords: High damping, Strain dependent damping, Copper alloys, Premartensitic effects, Flickering, Tweed microstructures, Manganese alloys, Theses. (mjm)