The thermal stability and mechanical behavior of selected Ti-base nanostructured alloys will be studied. The alloys will be prepared by mechanical alloying. Both hcp and bcc stabilized Ti-base alloys will be synthesized and appropriate ternary solutes added that can produce thermodynamic and kinetic stabilization of nanoscale microstructures at high temperature. The thermodynamic stabilization model developed in our previous research is used to identify alloy compositions, solutes, and temperature ranges that are favorable for thermodynamic stabilization. Nanoscale yittria particles will also be introduced by mechanical alloying as an alternative kinetic stabilization and strengthening mechanism.

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.

The research objective of this proposal is to test the hypothesis that a coining process can be used to create nanometer scale features in a high-precision diamond turning machine. A variety of optical components are currently created as a diamond turned molds and then transferred into plastic in the form of reflective tape or micro-optical arrays. Sub-wavelength optical features can add significant functionality to these optical devices; for example, small spherical bumps can create a non-reflective surface much like the eye of a moth or sub-wavelength features that produce dichroic (wave length sensitive) response. The proposed process could be less expensive than the current method using many layers of sputtered films and could be applied in selected regions of the surface providing additional flexibility. The technique involves a small die (30 µm square) with thousands of features that is attached to the end of a vibrating tool. The die is pressed into contact with the workpiece by the motion of the tool whose speed is adjusted to the speed of the workpiece such that the registration of the features occurs. For the die geometry envisioned and the speed of the tool, 500x106 features can be created per second. The project will involve four phases: coining die design and fabrication using a focused ion beam, actuator design and testing, material selection and nano-feature fabrication. If successful, this innovation will extend the capability of diamond machining to efficiently create arrays of sub-wavelength features.

While partial success has been achieved in optimization of mechanical properties for some nanostructured metals, their poor thermal stability has limited the use of these materials for processing and applications. The proposed research on Fe-Ni-Cr alloys, an important class of engineering alloys, will use selected dopants such as Zr to stabilize nanocrystalline alloys to high temperatures. This occurs by means of a thermodynamic stabilization mechanism that reduces the effective grain boundary energy to zero. Preliminary results show that additions of 2-4 at% Zr will stabilize pure Fe to temperatures above 900C. This strategy will be used to stabilize selected Fe-Ni, Fe-Cr and Fe-Ni-Cr alloy powders for thermal stabilization studies, hot compaction and characterization of the important mechanical proeprties.

This proposal is for collaborative research with the University of Vienna and IFW-Dresden as the Materials World Network of NSF. The research will focus on the processing-structure-property relationships in ultra-fine grained and nanocrystalline Cu and Cu-Zn alloys to determine their mechanical behavior and deformation mechanisms as a function of grain size and stacking fault energy. The collaboration of the three institutions is needed to allow for producing artifact-free samples across the grain size range of 1000 to 10 nm and for special characterization and mechanical testing facilities.

This project will show how micrometer-amplitude vibration of the tool can reduce the forces, improve the surface finish and decrease the wear in a diamond turning operation. Vibration Assisted Machining (VAM) was first developed in the 70s and is seeing more commercial applications from grinding of glass optics to diamond turning stainless steel injection molding dies. By selecting the amplitude and frequency of this motion, the tool can separate from the workpiece during the vibration cycle leading to the reported improvements in the machining process. While researchers throughout the world have published papers extolling the virtues of VAM, the results have been empirical and have not addressed the basic science behind such improvements. In this project, the effect of changing the process parameters will be studied within the context of the chemistry and hardness of the workpiece material, the temperature of the tool and chip, the wear of the diamond tool and the surface finish of the machined surface. It will study the process in detail, quantify the improvements in surface finish and tool wear and elucidate the reasons why such improvements are possible. The plan for the research involves three main tasks: 1) 1-4 KHz machining experiments and characterization, 2) analysis and modeling and 3) 20 KHz machining experiments. These tasks will define and corroborate the operating conditions that are required to gain the promised benefits promised and define the best way to produce these conditions.

This proposal is a request for an REU supplement for one undergraduate student to participate in the research activities supported by NSF grant #DMR-0412583, "Effect of Alloying and Thermo-Mechanical-Treatment on Anisotropic Creep and Deformation of Ti-alloys." The start date of the current request is 5/15th.

The major objective of the proposed research is to develop strategies to optimize the stabilization of nanoscale microstructures by a combination of experimental and modeling studies. Such optimization is needed for successful consolidation of particulates to bulk nanostructured materials without significant coarsening of the nanocrystalline microstructure. The approach will comprise a systematic experimental study of grain growth kinetics, with and without applied pressure, and the factors that influence it in selected nanostructured metals and alloys prepared by mechanical attrition. Analysis and modeling will be employed to identify the thermodynamic and kinetic mechanisms that can inhibit grain growth as a function of grain boundary structure and chemistry. Consolidation of nanostructured powders to obtain theoretical density and complete inter particle bonding will use optimized processing routes based upon the grain growth studies. Evaluation of the effectiveness of the thermomechanical consolidation processes will be carried out by measurement of selected mechanical properties.

The amorphous layers produced by single-point diamond turning of Si will be characterized using cross-section transmission electron microscopy (TEM). The aim is to correlate the transformation-dislocation damage morphologies with machining parameters. The latter will include the depth-of-cut, feedrate, crystallographic orientations (surface plane and cutting direction) and tool geometry. Raman depth profiling will be done in parallel with the machining and TEM studies on Si. The Raman results contain information on the a-Si layer depth and also the residual stresses. The latter will reflect both the a-Si layer constraint and the residual dislocation substructure. Stress/fracture-based machining models developed previously for ductile- regime machining of brittle materials will be extended to include both the HPPT and dislocation plasticity mechanisms along with the requisite fracture mechanics.

In this acquisition proposal, we are requesting a state-of-the-art nanoindenter with an integrated atomic force microscope. This instrument is a stand-alone test platform for the quantitative mechanical characterization of materials at the nanoscale. The unique capabilities of the nanoindenter will bring together 16 faculty members from three different colleges at North Carolina State University (NCSU) with a broad range of interests and expertise relevant to materials science based research. General areas critical to the current and future research programs of NCSU will be enabled through this acquisition. They include: Bulk and Thin Film Nanocrystalline Materials, Semiconductors and Ceramics, Nanoscale Organic Materials, Biomaterials.