| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
|
| Initial Amendment Date: | August 8, 2015 |
| Latest Amendment Date: | August 8, 2015 |
| Award Number: | 1536811 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Siddiq Qidwai
sqidwai@nsf.gov (703)292-2211 CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | October 1, 2015 |
| End Date: | September 30, 2019 (Estimated) |
| Total Intended Award Amount: | $340,000.00 |
| Total Awarded Amount to Date: | $340,000.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
4200 FIFTH AVENUE PITTSBURGH PA US 15260-0001 (412)624-7400 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
PA US 15213-2303 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Mechanics of Materials and Str |
| Primary Program Source: |
|
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
The metals used in mechanical components for small-scale devices at room temperature are normally of face center cubic character. Their mechanical behavior is generally well-known. However, at high temperature, these FCC metals become soft. Therefore, they are not suitable for high temperature application. In that case, body center cubic (BCC) nanostructured metals offer an alternative. These metals possess potentially desired high temperature strength. They are expected to serve in components in future high temperature device such as micro/nano electro-mechanical systems (MEMS/NMMS). Although the mechanical behavior of large-sized BCC metals is well-known, these macroscale properties cannot be directly used for nanometer-sized structures due to size effects. For the analysis of the small devices, it is necessary to know the mechanical behavior of BCC metals at small scales. However, there is lack of experimental data for the deformation process at small scales, and also there is no understanding of the deformation behavior of BCC metals at the nanometer scale. An in-situ mechanical testing approach inside a special high resolution transmission electron microscope (HRTEM) will be used in this research. This constitutes a new approach for studying the mechanical behavior at atomistic scale for nanometer-sized BCC metal specimens. The understanding of the mechanical behavior of nanometer-sized BCC crystals gained from this research will have direct impact on the design and fabrication of the high temperature MEMS/NEMS. The research on the in-situ HRTEM is expected to open a new approach to directly observe atomic-scaled deformation under mechanical stress. The results from the research are expected to contribute to the advancement of experimental mechanics and nanomaterials.
The research will employ an in-situ tensile technique utilizing the most advanced instrument of high resolution transmission electron microscope (HRTEM) to reveal the deformation process in nanometer-sized BCC metal specimens. Firstly, nanometer-sized high strength BCC metal specimens will be fabricated in-situ. Secondly, tensile/compression experiment in-situ in the HRTEM will be conducted on these BCC specimens to documents deformation behavior at room temperature and high temperatures; Thirdly, lattice disturbance, dislocation dipole nucleation and competition between slip and twinning in the deformation process will be observed. Molecular dynamics modeling on key issues with a) dislocation dipole formation; b) nucleation of twinning and dislocation and c) competition of twinning and slip as function of crystal orientation will be carried out. The experiments will be carried out via national user facilities at the Environmental Molecular Sciences Laboratory (EMSL), Pacific Northwest National Laboratory, Richland, WA. This collaboration will build national research infrastructure.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Body center cubic (BCC) nanostructures (especially refractory Groups) are expected to serve as significant component in future small scale structures such as high temperature MEMS/NMMS component due to their high temperature strength, while mechanical properties and deformation mechanisms in metallic face center cubic (FCC) nanostructures have been extensively studied. It is important to know the deformation behavior and mechanism in nanoscale BCC crystals, however, there is lack of such understanding on deformation mechanism, especially twinning deformation for nanoscale BCC crystals. This award supports research to acquire fundamental knowledge about the deformation mechanism for nano-sized BCC crystals at atomic scale through in-situ high resolution transmission electron microscope (HRTEM). The results attained in this research particularly enable rational design of nanoscale refractory BCC metals and alloys with high strength and ductility for high temperature MEMS/NMMS application in the future, and hence benefit the U.S. economy and society.
The intellectual merit: The research has lied in the novel experiment to employ an in situ tensile technique utilizing the most advanced instrument (HRTEM) with Cs correction to reveal the deformation process in nano-sized BCC crystals. We have fabricated high strength refractory BCC nanopilars of tungsten (W) and tantalum (Ta), and carried out the in-situ tensile/compressive experiments under Cs-corrected HRTEM; The in-situ HRTEM results from this research reveal that (1) Plastic deformation with mechanisms of dislocation slip, shear banding and twinning in the nanoscale BCC crystals is load-orientation dependent; (2) Deformation twinning in nanoscale BCC metals is nucleation-controlled. The size dependence of twinning mode (nucleation or growth) contributes to the size-dependent mechanical behaviors of the nanocrystals and (3) The twin stability and the detwinning process in nanoscale BCC crystals are strongly dependent on twin boundary type. Specifically, a unique structure of "inclined twin boundaries" has been found to play an important role in determining the stability of deformation twins, which is significant for the design and process of twin structures in nanoscale BCC alloys with prominent pseudoelasticity and self-healing behavior. The results from the research have been contributed to the advancement of in-situ mechanics and nanomaterials. The understanding on the mechanical behavior of the nano-sized BCC crystals is directly impacting on the design and reliability of the refractory BCC materials-based MEMS/NEMS for high temperature application.
Broader impact: The outcomes of the research have an impact on a broad range of fields (such as, experimental mechanics, nanoscale mechanics, nanoscale materials development, in-situ transmission electron microscopy and advanced MEMS/NMMS design) which employ nanoscale BCC metals/alloys to perform with high strength and ductility. The in-situ HRTEM approach developed from the research has been distributed in academic community and opened a new approach to directly observe atomic-scaled deformation. Furthermore, integration of research and education has been carried out through (1) training graduate students with their participation in DOE national laboratories, (2) graduate course development and (3) delivery of the movies on in-situ experiments to Pittsburgh Carnegie Science Museum for young students. The developed novel experimental technique has added new capabilities to the multi-user facilities at the University of Pittsburgh and Pacific Northwest National Laboratory. Twelve research articles have been published on peer-reviewed scientific journals, and multiple technical presentations have been delivered at national / international conferences. The research results on in-situ experiments have been added as teaching materials of graduate course. Through the entire life of the award, two PhD students received the research training in nanoscale experimental mechanics.
Last Modified: 10/01/2019
Modified by: Scott X Mao
Please report errors in award information by writing to: awardsearch@nsf.gov.
