{"385881":{"#nid":"385881","#data":{"type":"news","title":"Study helps understand why a material\u2019s behavior changes as it gets smaller","body":[{"value":"\u003Cp\u003ETo fully understand how nanomaterials behave, one must also understand the atomic-scale deformation mechanisms that determine their structure and, therefore, their strength and function.\u003C\/p\u003E\u003Cp\u003EResearchers at the University of Pittsburgh, Drexel University and the Georgia Institute of Technology have engineered a new way to observe and study these mechanisms and, in doing so, have revealed an interesting phenomenon in a well-known material, tungsten. The group is the first to observe atomic-level deformation twinning in body-centered cubic (BCC) tungsten nanocrystals.\u003C\/p\u003E\u003Cp\u003EThe team used high-resolution transmission electron microscope (TEM) and sophisticated computer modeling to make the observation. This work, published March 9 in the journal \u003Cem\u003ENature Materials\u003C\/em\u003E, represents a milestone in the in-situ study of mechanical behaviors of nanomaterials.\u003C\/p\u003E\u003Cp\u003EDeformation twinning is a type of deformation that, in conjunction with dislocation slip, allows materials to permanently deform without breaking. In the process of twinning, the crystal reorients, which creates a region in the crystal that is a mirror image of the original crystal. Twinning has been observed in large-scale BCC metals and alloys during deformation. However, whether twinning occurs in BCC nanomaterials or not remained unknown.\u003C\/p\u003E\u003Cp\u003E\u201cTo gain a deep understanding of deformation in BCC nanomaterials, we combined atomic-scale imaging and simulations to show that twinning activities dominated for most loading conditions, due to the lack of other shear deformation mechanisms in nanoscale BCC lattices.\u201d said Scott Mao, a professor in the Swanson School of Engineering at the University of Pittsburgh.\u003C\/p\u003E\u003Cp\u003EThe team chose tungsten as a typical BCC crystal. The most familiar application of tungsten is their use as filaments for light bulbs.\u003C\/p\u003E\u003Cp\u003EThe observation of atomic-scale twinning was made inside a TEM. This kind of study has not been possible in the past, due to difficulties of making BCC samples less than 100 nanometers in size, as required by TEM imaging. Jiangwei Wang, a graduate student at University of Pittsburgh, and Mao, the lead author of the paper, developed a clever way of making the BCC tungsten nanowires. Under a TEM, Wang welded together two small pieces of individual nanoscale tungsten crystals to create a wire about 20 nanometers in diameter. This wire was durable enough to stretch and compress while Wang observed the twinning phenomenon in real time using a high-resolution TEM.\u003C\/p\u003E\u003Cp\u003ETo better understand the phenomenon observed by Mao and Wang\u2019s team at the University of Pittsburgh, Christopher Weinberger, an assistant professor in Drexel\u2019s College of Engineering, developed computer models\u0026nbsp;that show the mechanical behavior of the tungsten nanostructure \u2013 at the atomic level. His modeling allowed the team to see the physical factors at play during twinning. This information will help researchers theorize why it occurs in nanoscale tungsten and plot a course for examining this behavior in other BCC materials.\u003C\/p\u003E\u003Cp\u003E\u201cWe\u2019re trying to see if our atomistic-based model behaves in the same way as the tungsten sample used in the experiments, which can then help to explain the mechanisms that allow it to behave that way,\u201d Weinberger said. \u201cSpecifically, we\u2019d like to explain why it exhibits this twinning ability as a nanostructure, but not as a bulk metal.\u201d\u003C\/p\u003E\u003Cp\u003EIn concert with Weinberger\u2019s modeling, \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/faculty\/t_zhu\u0022\u003ETing Zhu\u003C\/a\u003E, an associate professor in the \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/\u0022\u003EWoodruff School of Mechanical Engineering at Georgia Tech\u003C\/a\u003E, worked with a graduate student, Zhi Zeng, to conduct advanced computer simulations, using molecular dynamics to study deformation processes in 3-D.\u003C\/p\u003E\u003Cp\u003EZhu\u2019s simulation revealed that tungsten\u2019s \u201csmaller is stronger\u201d behavior is not without drawbacks when it comes to application.\u003C\/p\u003E\u003Cp\u003E\u201cIf you reduce the size to the nanometer scale, you can increase strength by several orders or magnitude,\u201d Zhu said. \u201cBut the price you pay is a dramatic decrease in the ductility.\u003Cbr \/\u003EWe want to increase the strength without compromising the ductility in developing these nanostructured metals and alloys. To reach this objective, we need to understand the controlling deformation mechanisms.\u201d\u003C\/p\u003E\u003Cp\u003EThe twinning mechanism, Mao added, contrasts with the conventional wisdom of dislocation nucleation-controlled plasticity in nanomaterials. The results should motivate further experimental and modeling investigation of deformation mechanisms in nanoscale metals and alloys, ultimately enabling the design of nanostructured materials to fully realize their latent mechanical strength.\u0026nbsp;\u003C\/p\u003E\u003Cp\u003E\u0022Our discovery of the twinning dominated deformation also opens up possibilities of enhancing ductility by engineering twin structures in nanoscale BCC crystals\u0022 Zhu said.\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332-0181\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003Es: Georgia Tech \u2013 John Toon (404-894-6986) (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) or the University of Pittsburgh \u2013 Joe Miksch (412-624-4356) (\u003Ca href=\u0022mailto:jmiksch@pitt.edu\u0022\u003Ejmiksch@pitt.edu\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: Joe Miksch, University of Pittsburgh\u003Cbr \/\u003E\u003Cbr \/\u003E\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EResearchers at the University of Pittsburgh, Drexel University and the Georgia Institute of Technology have engineered a new way to observe and study atomic-scale dislocation mechanisms in certain metals. In doing so, they have revealed an interesting phenomenon in a well-known material, tungsten.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have engineered a new way to observe and study dislocation mechanisms in tungsten."}],"uid":"27303","created_gmt":"2015-03-09 11:12:59","changed_gmt":"2016-10-08 03:02:55","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2015-03-09T00:00:00-04:00","iso_date":"2015-03-09T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"385831":{"id":"385831","type":"image","title":"Tungsten deformation","body":null,"created":"1449246262","gmt_created":"2015-12-04 16:24:22","changed":"1475894349","gmt_changed":"2016-10-08 02:39:09","alt":"Tungsten deformation","file":{"fid":"75410","name":"w_4.jpg","image_path":"\/sites\/default\/files\/images\/w_4.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/w_4.jpg","mime":"image\/jpeg","size":621988,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/w_4.jpg?itok=xIY5KOUo"}},"385851":{"id":"385851","type":"image","title":"Tungsten deformation research","body":null,"created":"1449246262","gmt_created":"2015-12-04 16:24:22","changed":"1475894400","gmt_changed":"2016-10-08 02:40:00","alt":"Tungsten deformation research","file":{"fid":"75412","name":"tungsten-twinning2559.jpg","image_path":"\/sites\/default\/files\/images\/tungsten-twinning2559.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/tungsten-twinning2559.jpg","mime":"image\/jpeg","size":1741320,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tungsten-twinning2559.jpg?itok=LKcj_h-X"}}},"media_ids":["385831","385851"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"531","name":"defect"},{"id":"120831","name":"dislocation"},{"id":"7082","name":"metal"},{"id":"92451","name":"Ting Zhu"},{"id":"120781","name":"tungsten"}],"core_research_areas":[{"id":"39431","name":"Data Engineering and Science"},{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39471","name":"Materials"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E(404) 894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}