Grain size effects on the fatigue response of nanocrystalline materials

The resistance of metals and alloys to fatigue crack initiation and propagation is known to be influenced significantly by grain size. Based on a wealth of experimental results obtained from microcrystalline metals, where the grain size is typically greater than 1 um, it is widely recognized that an increase in grain size generally results in a reduction in the fatigue endurance limit. On the other hand, a coarser grain structure can lead to an increased fatigue threshold stress intensity factor range, as well as a decrease in the rate of fatigue crack propagation. The relevance of these trends to ultra-fine-crystalline metals (grain size between 100 nm and 1000 nm) and nanocrystalline metals (grain size less than 100 nm) is relatively unknown. Such lack of understanding is primarily a consequence of the paucity of experimental data on the fatigue response of metals with very fine grains. In this work, the fatigue behavior of electrodeposited, fully dense, nanocrystalline pure Ni, with average and total range of grain sizes well below 100 nm, was examined. The fatigue response of nanocrystalline Ni was also compared with that of ultra-fine-crystalline and microcrystalline Ni wherever appropriate. It was found that grain refinement to the nanocrystalline regime generally leads to an increase in resistance to failure under stress-controlled fatigue whereas a deleterious effect was seen on the resistance to fatigue crack growth. To explore the generality of the above trends, similar experiments were performed on additional ultra-fine-crystalline material systems, produced using alternate processing techniques such as cryomilling and equal channel angular pressing.

Department dc:contributor.department

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

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Hanlon, Timothy, 1977-

Advisor dc:contributor.advisor

• Subra Suresh.

• 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/1721.1/16635

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16635