It is well known that there exists a "banana" curve for the strength and ductility of metals and alloys, where a material is either strong or ductile, but rarely both at the same time. Both high strength and high ductility are desired for structural applications. Recently, we found that Ti with heterogeneous lamella (HL) structure can be made to possess both high strength and high ductility, avoiding the curse of the ����������������banana curve���������������. In this structure, the soft large-grained lamellae are surrounded by hard ultrafine-grained matrix, which is opposite to the conventional microstructure. Importantly, the addition of soft lamella to the ultrafine-grained hard matrix did not lower the global strength, which is against the principle that we know from textbook and literature. Furthermore, this unique structure has even higher strain hardening rate than coarse-grained Ti, which is again extraordinary. This high strain hardening ensured its high ductility. If this discovery can be applied to other metals and alloys, it has the potential to revolutionize the structural metals and alloys industry and related applications. It should be noted that the HL structure is very different from the conventional ����������������bi-modal��������������� structure. The HL structure has high density of lamella interfaces, which is a critical requirement for superior properties. Ti has a hexagonal close-packed (hcp) crystal structure, which has specific deformation texture and other characteristics from rolling. It is therefore important to study if metals and alloys with other crystal structures (e.g. fcc) can also be processed to produce the HL structure and superior properties. In this proposed Short Term Innovative Research (STIR) project, I propose to investigate if heterogeneous lamella structure can also be formed in fcc metals to produce a superior combination of strength and ductility. Metals with fcc crystal structure have abundant slip systems, and should deform very differently from hcp Ti. Nevertheless, it is my hypothesis that similar structure and properties can be produced in fcc metals and alloys. The objective of this research is threefold: 1) to verify the feasibility of producing HL structure in fcc metals, 2) to produce a combination of strength and ductility that is not accessible to corresponding conventional homogeneous fcc metals and 3) to probe fundamental science on how the HL structures are affected by processing parameters.

In support of this Air Force Phase I SBIR program, the PI at North Carolina State University and his group will perform the following tasks: 1. Fabricate and characterize carbon nanotube / copper composites in the shape of sheets, approximately 1��������������� wide by 12��������������� long with CNTs oriented along the width. 2. Provide carbon nanotube/copper composite prototypes to Triton. 3. Participate in teleconferences on at least a monthly basis with Triton and/or the Air Force. 4. Contribute to Triton������������������s technical progress reports to Air Force.

This projected is funded by Jianyin Xingcheng Special Steel Co. Ltd, China. We will use Surface Mechanical Attrition Treatment (SMAT) to produce a nano layer on the steel plate surface, and then evaluate the improvement in corrosion resistance, wear resistance and fatigue life. This is a cooperative project with active participation of the company.

The research work addresses the development of Fe-Cr alloys that have improved performance for nuclear energy applications. Alloy additions will be made to engineer the microstructures for this purpose. The goal is to achieve alloys that are stable to high temperatures and also have good strength properties and resistance to radiation damage. The processing routes that have been used in previous work are based on alloy additions that produce a fine-scale dispersion of nanometer size oxide particles in alloys with grain sizes well above the nanoscale (< 100 nm). The oxide particles increase strength and provide interfacial area that improves radiation resistance. Based on our current work for stabilizing a nanoscale grain size by adding appropriate solutes that segregate to grain boundaries and eliminate the driving force for grain growth at high tempertures (thermodynamic stabilization), we propose to combine this approach with concurrent alloy additions that produce nanoscale oxide dispersions. This is expected to have significant benefits to both strengthening and radiation resistance. A nanoscale grain size adds to the strength by the Hall-Petch effect and it will also substantially increase interfacial area to improve radiation resistance.

Carbon nanotubes have been shown to possess unique mechanical, thermal and electrical characteristics. Previous work by the P.I. and North Carolina State University on properties of carbon nanotube (CNT) tape uni-directional composites demonstrated not only superior mechanical and thermal properties, but also piezoresistive properties. The next property, which should be tested, is piezoelectric effects in CNT tape. This property along with the known piezoresistivity would open the way for a number of sensor applications beneficial to not only NASA, but DOD and commercial interests as well. Sensors such as gyroscopes (vibration) and accelerometers normally utilize silicon as the reactive electrical element. These silicon elements require expensive and time-consuming micro machining. The ease of manufacture and low cost of CNT tape gives these materials distinct advantages over silicon for these applications. It is planned in this research to first test the piezoelectric response of CNT tape. Polyvinylidine fluoride (PVDF) is a known piezoelectric material. To enhance any piezoelectric effect of the CNT tape, PVDF films will be sandwiched between layers of CNT tape. Since PVDF is thermoplastic, simple hot pressing will allow a sandwich structure to be obtained. The testing will be done in the Microfabrication Lab in the Aviation and Missile Research, Development, and Engineering Center (AMRDEC). Once the testing is complete, a prototype vibration gyroscope will be constructed and tested. Utilizing the piezoresistive nature of CNT tape it is also planned to construct a prototype accelerometer. Also, direct comparison of the strain sensitivity of CNT tape with a commercial strain gauge will allow us to determine if these tapes can be utilized for structural health monitoring sensors. The already demonstrated superior mechanical and thermal properties along with unique electrical characteristics and ease of manufacture make CNT tape an innovative material for proposed uses in various sensor technologies.

The light weight of Mg alloys make them very attractive for many structural applications including energy efficient vehicles and transportable bridges. However, Mg alloys have relatively low strength, ductility, and formability. Nanostructured Mg alloys have been studied in recent years to improve their strength and ductility, however, these are mostly done by trial and error approaches with limited success. It is critical to understand the fundamental deformation mechanisms of nanostructured Mg alloys so that we can effectively design them for high strength and good ductility. We have successfully carried out a Short Term Innovative Research Program (STIR) project, in which we activated the deformation twinning and a new slip system in the nanocrystalline Mg-Ti. Deformation twinning is rarely observed in nanocrystalline hcp metals due to grain size effect on the deformation mechanisms. In this proposed project, we will continue this effort to probe the deformation mechanisms in nanostructured Mg alloys. It is expected that new slip systems, new twinning mechanisms, and stacking faults on new crystal planes might be activated. The effect of new deformation mechanisms on the mechanical behaviors will be probed, and this study will help us design nanostructured Mg alloys for unprecedented strength and good ductility.

Producing unidirectional carbon nanotube (CNT) composites with a structural morphology identical to aerospace grade carbon fiber composites is a challenging task that no research groups have accomplished. This research team has recently demonstrated the ability to produce high volume fraction CNT composites with a high level of alignment, low level of CNT waviness and uniform distribution of polymer surrounding CNTs. This accomplishment has allowed for initial record breaking strengths higher than their carbon fiber composite counterparts. The research objective of this proposed work is to build on those accomplishments by replacing the polymer matrix with a carbon/graphite matrix. The resulting composites will resemble carbon-carbon composites utilized in the aerospace industry with a nanostructured architecture of aligned CNTs. Through high temperature heat treatments the carbon matrix will be bonded to the CNTs, producing a highly crosslinked, high elastic modulus, low density material.

Nanocrystalline (nc) materials have high strength but usually low ductility, which has been a major issue for their structural applications. Deformation twinning has been shown to be able to simultaneously improve both strength and ductility. In addition, twin boundaries have been reported to enhance the thermal stability and to retain better electrical conductivity than grain boundaries. Therefore, it is critical to understand the mechanisms of deformation twinning so as to design nc materials for superior mechanical and physical properties. However, our understanding of twinning mechanisms is still very limited. For example, we have experimentally observed both normal and inverse grain size effect on deformation twinning in nc fcc Ni. This phenomenon cannot be fully explained by our current understanding. In addition, there is no theoretical model to satisfactorily describe all of the experimental observations on deformation twinning in nc materials, in large part due to the lack of good understanding of the following issues: i) the mechanism of the grain size effect on the nucleation of deformation twins and stacking faults, ii) the effect of generalized planar fault energies (GPFEs) on the nucleation of twins and stacking faults, iii) effect of GPFEs on the spacing of twin boundaries. We propose a comprehensive study to investigate the above fundamental issues. Nanocrystalline fcc Al, Ni, and Cu films with controlled grain size and very narrow grain size distribution will be synthesized by self-assembly using pulsed laser deposition. These metals will also be processed to obtain a range of nano-grain sizes by the surface mechanical attrition technique. The systematic variation of grain size and GPFEs in these samples will enable us to fully probe the above fundamental issues. We will use high-resolution transmission electron microscopy to observe deformation twins and stacking faults. The fundamental mechanisms derived from these experiments will provide a basis for the analytical modeling that will take into account the effects of both grain size and GPFEs

This collaborative research project integrates the expertise at the Army Research Laboratory (ARL) and North Carolina State University (NCSU) on materials research and development of nanostructured metallic alloys to assess a new nanotechnology, Surface Mechanical Attrition Treatment (SMAT). It will develop a two-year collaboration between the two organizations through procurement of surface mechanical attrition treatment (SMAT) instrumentation, and its implementation for research projects of interest to both ARL and NCSU. The scope of the project is 1) Acquisition and installation of fully operational SMAT instrumentation for fabrication of nanostructured metallic surfaces. 2) Support current and future ARL mission programs in the area of nanostructured alloys through novel SMAT processing. 3) Characterization of wear, corrosion resistance and strength property enhancements as a result of SMAT processing.

The University of Delaware (PI: Prof. Tsu-Wei Chou) and the NC State University (NCSU) are submitting a joint proposal, entitled 'Multifunctional Flexible Composites Based on Continuous Carbon Nanotube Fiber,' to AFOSR. The proposed research aims to establish the scientific foundation for development of continuous carbon nanotube fiber-based multifunctional flexible composites for Air Force applications. It encompasses the following objectives: (1) Synthesize long spinnable carbon nanotube arrays, (2) Fabricate continuous carbon nanotube fibers, (3) Develop the processing science for thin, flexible composites reinforced with carbon nanotube fibers, (4) Characterize the physical and mechanical performance of the nanotube fiber, unidirectional lamina and flexible laminate, (5) Establish a comprehensive modeling/analysis capability for optimizing the composite multi-functionality through nano-, micro- and macro-structural design at the fiber, lamina and laminate levels, and (6) Construct composites multifunctional 'performance maps.' NCSU is responsible for (1) Synthesize long spinnable carbon nanotube arrays, (2) Fabricate continuous carbon nanotube fibers, and part of (4): Characterize the mechanical performance of the nanotube fiber.