{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/101560"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/101560","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Microstructure design of mechanically alloyed materials","abstract":"Nanocrystalline metals have exceptional mechanical properties that make them attractive for structural applications. However, these materials' properties tend to degrade due to grain growth when they are exposed to high temperatures; this makes producing bulk, nanocrystalline components particularly difficult as the most promising synthesis methods involve high temperature densification of powders or foils. Several alloy design strategies have been developed to overcome these thermal stability issues, but their efficacy depends on the spatial distribution of the stabilizing element in the feedstock materials, which are typically prepared using extensive plastic deformation or mechanical alloying. There is thus a need to predict the chemical mixity of mechanically alloyed materials, and this thesis seeks to address this need. To this end, phase strength effects are incorporated into a kinetic Monte Carlo simulation of a mechanically-driven, binary alloy, which can provide quantitative insight into the combination of processing and material parameters that dictate the steady state chemical mixity. Using such simulations, dynamical phase diagrams are generated that predict temperatures and compositions at which a couple with a given phase strength mismatch should chemically homogenize during mechanical alloying. Several of these dynamical phase diagrams are validated using mechanical alloying experiments, in which tungsten-transition metal couples with various phase strength mismatches are mechanically alloyed in a high energy ball mill. This thesis also describes an alloy design case study in which the insights from these simulations and experiments are used to develop a nanocrystalline W-based (W-7Cr-9Fe, at%) alloy powder that can be rapidly compacted to high relative densities while maintaining ultrafine grain sizes. Two-phase compacts made from the alloy exhibit microhardnesses of 13 GPa and dynamic compressive strengths in excess of 4 GPa. Furthermore, postmortem images of compressed micropillars machined out of these compacts suggest that this alloy deforms by shear localization. The penetration performance of this alloy is explored in sub-scale ballistic tests into concrete targets, and is found to be at least as good as current state-of-the-art penetrator materials.","abstract_html":"Nanocrystalline metals have exceptional mechanical properties that make them attractive for structural applications. However, these materials' properties tend to degrade due to grain growth when they are exposed to high temperatures; this makes producing bulk, nanocrystalline components particularly difficult as the most promising synthesis methods involve high temperature densification of powders or foils. Several alloy design strategies have been developed to overcome these thermal stability issues, but their efficacy depends on the spatial distribution of the stabilizing element in the feedstock materials, which are typically prepared using extensive plastic deformation or mechanical alloying. There is thus a need to predict the chemical mixity of mechanically alloyed materials, and this thesis seeks to address this need. To this end, phase strength effects are incorporated into a kinetic Monte Carlo simulation of a mechanically-driven, binary alloy, which can provide quantitative insight into the combination of processing and material parameters that dictate the steady state chemical mixity. Using such simulations, dynamical phase diagrams are generated that predict temperatures and compositions at which a couple with a given phase strength mismatch should chemically homogenize during mechanical alloying. Several of these dynamical phase diagrams are validated using mechanical alloying experiments, in which tungsten-transition metal couples with various phase strength mismatches are mechanically alloyed in a high energy ball mill. This thesis also describes an alloy design case study in which the insights from these simulations and experiments are used to develop a nanocrystalline W-based (W-7Cr-9Fe, at%) alloy powder that can be rapidly compacted to high relative densities while maintaining ultrafine grain sizes. Two-phase compacts made from the alloy exhibit microhardnesses of 13 GPa and dynamic compressive strengths in excess of 4 GPa. Furthermore, postmortem images of compressed micropillars machined out of these compacts suggest that this alloy deforms by shear localization. The penetration performance of this alloy is explored in sub-scale ballistic tests into concrete targets, and is found to be at least as good as current state-of-the-art penetrator materials.","abstract_has_math":false,"creators":["Cordero, Zachary C. (Zachary Copoulos)"],"institution":"Massachusetts Institute of Technology","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Materials Science and Engineering.","school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015","date_published":"2015","updated_at":"2026-07-22T22:21:49Z","subjects":["Materials Science and Engineering."],"languages":["eng"],"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."],"rights_urls":["http://dspace.mit.edu/handle/1721.1/7582"],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1721.1/101560","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. Department of Materials Science and Engineering."]},{"key":"dc:contributor.other","label":"Dc Contributor Other","values":["Massachusetts Institute of Technology. Department of Materials Science and Engineering."]},{"key":"dc:creator","label":"Author","values":["Cordero, Zachary C. (Zachary Copoulos)"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2016-03-03T21:09:01Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2016-03-03T21:09:01Z"]},{"key":"dc:date.issued","label":"Date","values":["2015"]},{"key":"dc:publisher","label":"Institution","values":["Massachusetts Institute of Technology"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Materials Science and Engineering."]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["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."]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://dspace.mit.edu/handle/1721.1/7582"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1721.1/101560"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.","Cataloged from PDF version of thesis.","Includes bibliographical references (pages 107-120)."]},{"key":"dc:description.abstract","label":"Abstract","values":["Nanocrystalline metals have exceptional mechanical properties that make them attractive for structural applications. However, these materials' properties tend to degrade due to grain growth when they are exposed to high temperatures; this makes producing bulk, nanocrystalline components particularly difficult as the most promising synthesis methods involve high temperature densification of powders or foils. Several alloy design strategies have been developed to overcome these thermal stability issues, but their efficacy depends on the spatial distribution of the stabilizing element in the feedstock materials, which are typically prepared using extensive plastic deformation or mechanical alloying. There is thus a need to predict the chemical mixity of mechanically alloyed materials, and this thesis seeks to address this need. To this end, phase strength effects are incorporated into a kinetic Monte Carlo simulation of a mechanically-driven, binary alloy, which can provide quantitative insight into the combination of processing and material parameters that dictate the steady state chemical mixity. Using such simulations, dynamical phase diagrams are generated that predict temperatures and compositions at which a couple with a given phase strength mismatch should chemically homogenize during mechanical alloying. Several of these dynamical phase diagrams are validated using mechanical alloying experiments, in which tungsten-transition metal couples with various phase strength mismatches are mechanically alloyed in a high energy ball mill. This thesis also describes an alloy design case study in which the insights from these simulations and experiments are used to develop a nanocrystalline W-based (W-7Cr-9Fe, at%) alloy powder that can be rapidly compacted to high relative densities while maintaining ultrafine grain sizes. Two-phase compacts made from the alloy exhibit microhardnesses of 13 GPa and dynamic compressive strengths in excess of 4 GPa. Furthermore, postmortem images of compressed micropillars machined out of these compacts suggest that this alloy deforms by shear localization. The penetration performance of this alloy is explored in sub-scale ballistic tests into concrete targets, and is found to be at least as good as current state-of-the-art penetrator materials."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph. D."]},{"key":"dc:title","label":"Title","values":["Microstructure design of mechanically alloyed materials"]}]}],"canonical_facts":{"dc:contributor.department":["Massachusetts Institute of Technology. Department of Materials Science and Engineering."],"dc:contributor.other":["Massachusetts Institute of Technology. Department of Materials Science and Engineering."],"dc:creator":["Cordero, Zachary C. (Zachary Copoulos)"],"dc:date.accessioned":["2016-03-03T21:09:01Z"],"dc:date.available":["2016-03-03T21:09:01Z"],"dc:date.issued":["2015"],"dc:description":["Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.","Cataloged from PDF version of thesis.","Includes bibliographical references (pages 107-120)."],"dc:description.abstract":["Nanocrystalline metals have exceptional mechanical properties that make them attractive for structural applications. However, these materials' properties tend to degrade due to grain growth when they are exposed to high temperatures; this makes producing bulk, nanocrystalline components particularly difficult as the most promising synthesis methods involve high temperature densification of powders or foils. Several alloy design strategies have been developed to overcome these thermal stability issues, but their efficacy depends on the spatial distribution of the stabilizing element in the feedstock materials, which are typically prepared using extensive plastic deformation or mechanical alloying. There is thus a need to predict the chemical mixity of mechanically alloyed materials, and this thesis seeks to address this need. To this end, phase strength effects are incorporated into a kinetic Monte Carlo simulation of a mechanically-driven, binary alloy, which can provide quantitative insight into the combination of processing and material parameters that dictate the steady state chemical mixity. Using such simulations, dynamical phase diagrams are generated that predict temperatures and compositions at which a couple with a given phase strength mismatch should chemically homogenize during mechanical alloying. Several of these dynamical phase diagrams are validated using mechanical alloying experiments, in which tungsten-transition metal couples with various phase strength mismatches are mechanically alloyed in a high energy ball mill. This thesis also describes an alloy design case study in which the insights from these simulations and experiments are used to develop a nanocrystalline W-based (W-7Cr-9Fe, at%) alloy powder that can be rapidly compacted to high relative densities while maintaining ultrafine grain sizes. Two-phase compacts made from the alloy exhibit microhardnesses of 13 GPa and dynamic compressive strengths in excess of 4 GPa. Furthermore, postmortem images of compressed micropillars machined out of these compacts suggest that this alloy deforms by shear localization. The penetration performance of this alloy is explored in sub-scale ballistic tests into concrete targets, and is found to be at least as good as current state-of-the-art penetrator materials."],"dc:description.degree":["Ph. D."],"dc:identifier.uri":["http://hdl.handle.net/1721.1/101560"],"dc:language.iso":["eng"],"dc:publisher":["Massachusetts Institute of Technology"],"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."],"dc:rights.uri":["http://dspace.mit.edu/handle/1721.1/7582"],"dc:subject":["Materials Science and Engineering."],"dc:title":["Microstructure design of mechanically alloyed materials"],"dc:type":["Thesis"]},"updated_at":"2026-07-22T22:21:49Z"}