Stability of nanostructured : amorphous aluminum-manganese alloys

Nanocrystalline alloys have attracted interest for decades because of their improved mechanical strength without sacrificing ductility, but structural stability has always been an issue. In this work, bulk aluminum-manganese (Al-Mn) nanocrystalline alloys have been synthesized using room temperature ionic liquid electrodeposition, by which various nanostructures and dual-phase structures can be created by controlling the Mn solute incorporation level. The manganese exhibits grain boundary segregation in the Al-Mn solid solution in the as-deposited condition, which contributes to enhanced stability of the nanostructure. The grain boundary properties of the nanostructured alloys were studied via three dimensional atom probe tomography and aberration-corrected scanning electron microscopy. The segregation energies were calculated based on the experimental results and compared with the values calculated from a thermodynamic-based segregation model. Upon heating of the nanostructured and dual-phase alloys, a variety of complex phase transformations occur. A combination of X-ray diffraction, transmission electron microscopy, as well as differential scanning calorimetry were employed to understand the phase transformation mechanisms and grain growth processes. A Johnson-Mehl-Avrami-Kolmogorov analytical model was proposed as a descriptive method to explain the phase transformation sequence. Using the parameters extracted from the analytical model, predictive time-temperature transformation diagrams were constructed. The stability region of the alloy in time-temperature space is thus established, providing a simple way to evaluate nanostructure stability.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2016

Author dc:creator

• Huang, Ting-Yun Sasha

Advisor dc:contributor.advisor

• Christopher A. Schuh.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/104107

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/104107