Transformation-superplasticity of metals and metal matrix composites

The work covers transformation superplasticity of metals, alloys and metal matrix composites. Fundamental studies of transformation superplasticity in unreinforced metals, which either deform plastically or by creep, form the basis of further investigations in metal matrix composites. Experiments and analytical modeling are complemented by numerical analysis. The transformation superplastic behavior is related to microstructure and chemical composition. Based on an existing linear theory, a non-linear model is developed and applied to the experimental data. Numerical methods are used to model the stress-, strain and temperature evolution during the phase transformation. The results are in good agreement with the experiment and analytical predictions. First, transformation superplasticity of iron and iron-TiC composites is demonstrated with strains of 450% and 230% respectively. The reduction of the transformation superplasticity in the composites is attributed to the dissolution of TiC in iron and effect which is shown for iron-carbon alloys. Effects of transient primary creep, ratchetting and partial transformation through the ferrite-austenite phase field are examined. Second, transformation superplasticity of zirconium is demonstrated for the first time with a strain of 270% without fracture. Partial transformation resulting from high cycle frequencies is analyzed and related to material properties and cycle characteristics. Finally, nickel aluminide with unstabilized zirconia particulates shows significant higher strain rates upon thermal cycling as compared to the unreinforced matrix. Although, the fracture strain of 23% is below the superplastic limit, the composite shows a high strain rate sensitivity of m = 0.71, which is a necessary characteristic of transformation superplasticity.

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

1998

Author dc:creator

• Zwigl, Peter, 1963-

Advisor dc:contributor.advisor

• David C. Dunand.

• 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/1721.1/49665

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/49665