The Research Partnership

Eleven faculty (six from FAMU and five from CMU- MRSEC) will form five research teams with the focus on grain boundary engineering and magnetic processing. The research groups will meet regularly to discuss research progress, with the CMU faculty members participating through a video internet link. The research groups will submit biannual progress reports that will be reviewed by the PREM executive committee. The research groups/projects are summarized below:

		1 - The Role of Five-Parameter Grain Boundary Character in the Properties of Thin Film and Superplastic Materials, P.N. Kalu (FAMU) and A. Rollett (CMU)
		2 - Partnership in Magnetism and magnetic processing, Ke Han (FAMU), J. Schwartz (FAMU) and M. E. McHenry (CMU)
		3 - The use of Chiral Surfaces to Control Specific Polymeric Crystal Growth, R.G. Alamo (FAMU) and G. Rohrer (CMU)
		4 - Materials Improvement of Superconducting Electronic Devices, E. E. Kalu (FAMU), and P. Salvador (CMU)
		5 - Processing Model For Polycrystalline Micro and Nano Structured Materials, P.J. Gielisse (FAMU) and K. Barmak (CMU)

1- The Role of Five-Parameter Grain Boundary Character in the Properties of Thin Films and Superplastic Materials: P.N. Kalu (FAMU) and A. Rollett (CMU)

We propose to study the five-parameter grain boundary character of thin films and superplastic aluminum alloys for aerospace applications. The results will be used to optimize grain boundary engineering of these materials. The characterization of grain boundary character will be conducted using the state-of-the-art tools developed by the Mesoscale Interface Mapping Project that allow single plane sections to be used without the need for serial sectioning [Larsen, 2000a,b; Saylor, 2002]. The contribution of boundaries to superplastic deformation will be assessed through techniques such as measurement of displacements of fiducial lines on the surface. Correlations between the mechanical behavior of boundaries and their crystallographic type will be developed. Provided that a suitable formulation of the problem can be identified, a collaboration with the Materials Sensitive Design effort will be put in place to optimize microstructure with respect to superplastic response.
The proposed study will involve both orientation determination using Orientation Imaging Microscopy (OIM), and stereological analysis of boundary traces. Also, the project is expected to pose many practical challenges for the students. Some of the practical aspects of the project that deserves attention include (a) polishing techniques and (b) the choice of employing optical versus scanning electron microscopy in the imaging of the microstructures. Students from CMU and FAMU will work together on the various aspects of the problem. For example, John Conn, a Masters student at FAMU, spent the summer of 2002 at CMU learning some of the required techniques. Students from FAMU will therefore receive training in sample preparation, SEM operation, optical microscopy, stereology, interfacial crystallography and orientation imaging microscopy. It is anticipated that the knowledge gained in the work on aluminum alloys will be extended to other superplastic alloy systems.

2- Partnership in Magnetism and Magnetic Processing: Ke Han (FAMU), J. Schwartz (FAMU) and M. E. McHenry, CMU

The magnetic anisotropy of a material determines the variation of magnetic properties, such as permeability and susceptibility, with geometric direction. Anisotropy can be induced by annealing in the presence of a magnetic field. A key requirement is the presence of differing atomic species that form ordered atomic pairs aligned with the field. [Chikazumi, 1997]. The result of magnetic field annealing is a uniaxial anisotropy in the direction of the applied field.
An important application of induced anisotropy is linearizing the hysteresis loop. Applying the annealing field in a direction transverse to the magnetic path will shear the loop and result in a linear B-H relationship, as illustrated in Figure 1. The magnetization process is dominated by the rotation of moment vectors within domains, and domain wall motion is minimized. Power loss due to irreversible wall motion past defects is minimized.

Figure 1. Effect of field annealing on hysteresis loop of amorphous Metglas alloy. Figure from Honeywell web site.

Recently, a new class of nanocrystalline magnetic materials have been developed that are composed of a dispersion of 10-50 nm sized ferromagnetic grains embedded in a residual, amorphous, ferromagnetic matrix. The FINEMET [Yoshizawa, 1989] series of alloys contains DO3 Fe-Si grains and the NANOPERM [Makino, 1985] alloys contain A2 Fe grains. HITPERM [Willard, 1998] is an A2(B2) FeCo based alloy. These materials are produced by annealing an amorphous precursor which precipitates the nanocrystalline grains.
There are two possible field annealing routes for these alloys. In the first, a previously crystallized alloy is annealed at some temperature below that which the residual amorphous matrix decomposes into unwanted secondary phases. In the second, the amorphous precursor is field annealed and the nanocrystalline grains are precipitated in the presence of a field. In addition to pair ordering, the field crystallization technique holds potential for controlling the crystalline texture of the precipitated grains. This would allow magnetocrystalline anisotropy as well as induced anisotropy to be controlled.
HITPERM alloys are expected to have a stronger response to field annealing for two reasons. First, the presence of Co in addition to Fe may allow another pair ordering process to become active. Second, Co raises the Curie temperature of both the nanocrystalline grains and the amorphous matrix. Hence, the nanocomposite structure will be ferromagnetic at the annealing and crystallization temperatures. This will allow an anisotropy to be induced in the entire material, rather than in just the nanocrystalline grains.
In the first set of experiments, toroidal cores of HITPERM have been produced in the amorphous and nanocrystalline state. These cores are to be stacked in a superconducting solenoid to orient the applied field transverse to the magnetic path of the core. The proposed annealing profile is 20 T at 480 °C for 1 hour. This temperature will both crystallize the amorphous samples and field anneal the previously crystallized samples. The samples will be characterized at CMU and NASA Glenn Research Center. The second set of experiments will vary the annealing temperature to study the effects on crystallization kinetics. Higher fields (up to 32 T) will be attempted as they become available. Compositional variations will be attempted in the third round of experiments. Ni will be added to the Fe and Co to try to activate another pair ordering process.
Magnetic materials will be characterized by magneto-optical imaging. This technique facilitates real-time visualization of magnetic flux profiles via an optical microscope. A (Y,Bi,Pr,Lu)3(FeGa)5O12 indicator film is placed on top of the sample, within a small magnet, on the stage of an optical microscope. The polarization angle of the light is then modified by Faraday rotation, thus providing a mapping of the magnetic flux profile. This technique then gives quantitative results regarding the magnetic behavior of the samples. Furthermore, the magneto-optical imaging system at FSU has a unique in-situ tensile stage, which facilitates real-time imaging of the effects of tensile strain on the magnetic behavior.

3- The Use of Chiral Surfaces to Control Polymeric Crystal Growth: R.G. Alamo (FAMU) and G. Rohrer (CMU)

Nucleating agents are commonly used in processing isotactic polypropylenes and many other semi-crystalline polymers to increase the overall crystallization rate. This practice is used especially in the production of films and a diversity of injection molded parts that are used in automotive, microelectronics and biomedical industries [Foxley, 1996, Resins report.1998]. Semicrystalline polymers offer the combination of strength conferred by the crystalline regions and toughness provided by the finely dispersed non-crystalline regions. The most commonly observed crystallographic polymorph in isotactic polypropylene is the monoclinic or alpha form. The lamellar morphology associated with this crystallographic form is unusual. Transversal lamellae grow epitaxially from those initially formed, giving a mesh type crosshatched morphology [Brückner, 1991]. On a molecular basis, the branching is initiated on a lateral (010) face made up of chains of a given hand by the deposition of chains of the same hand, whereas the crystal structure of the alpha modification would call for chains of the opposite hand. Structurally this branching corresponds to a homoepitaxy and it is favored by a satisfactory interdigitation of the methyl groups of facing planes and by the near identity of the a and c parameters of the monoclinic unit cell of iPP, a = 6.65 Å, b = 20.96 Å, c = 6.5 Å, b = 99°. The thermodynamic and kinetic factors governing the formation and nature of the lamellar cross-hatching in iPP were studied for different types of polypropylenes. It was found that at the lower crystallization temperatures cross-hatching is profuse, while the characteristics of the lamellar branching were not uniform across the film surface [Huang, 2000; Bassett, 1984; Norton, 1985]. At the highest crystallization temperatures, a mesh-type crosshatching was not any longer formed. Instead, long thick radial lamellae crystallize first and thin short transversal ones were found to develop with increasing crystallization time and branch from the thick lamellae. In order to enhance uniformity in the geometrical arrays of lamellar branching during homoepitaxial crystallization, we plan to use chiral inorganic compounds available in Prof. Rohrer’s group as nucleating agents to provide a specific surface that may promote directional growth. Different types of substrates at low concentrations (typical of those used in industrial processes) will be tested. Growth and overall crystallization rates of the iPPs with and without the chiral compounds will be measured with standard optical microscopy and differential scanning calorimetry. The lamellar habits will be imaged by Atomic Force Microscopy.

A FAMU student will spend two months at the laboratory of Prof. Rohrer preparing the substrates and analyzing the initial lamellar morphology by OM and AFM. Further on, the linear growth rates and overall crystallization rates will be studied at the FAMU/FSU College of Engineering. The results may impact a number of technologically important areas because they will open the possibility of controlling diffusion in films and injection molded objects with well-defined nano-lamellar structures.

4- Materials Improvement of Superconducting Electronic Devices: E. E. Kalu (FAMU) and P. Salvador (CMU)

The synthesis and processing of high temperature superconductor thin films is key for the improvement of electronic devices. This project will focus on correlating the processing, microstructure, and electromagnetic properties of Hg-Ba-Ca-Cu-O, which has the highest critical temperature of any known superconductor. Only by relating the grain boundary chemistry to the superconducting properties, and subsequently developing synthesis and processing protocols that influence the grain boundary properties, will advances be possible.

Although the critical temperature of a superconducting material is the first indicator of its potential functionality in an engineering system, ultimately its transport current density in field and at temperature determines its utility. In high temperature superconductors, the critical current density is orthotropic, correlating to the highly aspected, orthotropic crystal structure. Furthermore, because the coherence length is significantly smaller than the typical grain boundary scale length, the grain-boundary chemistry and orientation relative to the crystallographic orientation often dominates the superconducting properties.

In this collaboration, the impact of synthesis, processing, substrate orientation, and substrate/superconductor lattice matching on grain boundary orientation will be explored using OIM and TEM. Furthermore, using the extensive superconducting property characterization facilities available at FAMU, the relationships between grain boundary chemistry and orientation and superconducting properties for the Hg-Ba-Ca-Cu-O superconductors will be established. These relationships will then drive subsequent approaches to synthesis and processing.

5- Processing Model for Polycrystalline Micro and Nano Structured Materials, P.J. Gielisse (FAMU) and K. Barmak (CMU)

The overall objective in the proposed effort is the generation of a processing model that would allow for the quantitative evaluation of the impact that material properties and processing parameters make on the performance of polycrystalline micro and nano structures of importance in microelectronic applications. The continuing increase in device density, along with penetration of control and communication electronics into high temperature industrial environments, (500°C and up) demand the availability of large area (300 mm diameter), high thermal conductivity surfaces (substrates) that can act as heat transfer and heat sinking media.

Current ceramic polycrystalline materials for these purposes are made up of individual macro grains bonded by a mostly amorphous phase forming the so-called grain boundaries. The nature and properties of the grain boundaries often remain unknown. One also encounters grain to grain (point, line, or surface) contacts as well as porosity within the grains and at the junctions of grains. These departures from perfection substantially lower the property values of the material such as the thermal or electrical conductivity, and the thermal shock resistance. The major stumbling block in the development of high quality polycrystalline substrates is the lack of a processing model, which would allow for the quantitative evaluation of the impact that various material properties and process parameters have on the performance of such structures. The initial research approach will involve a parametric study that will reveal the contribution of a variety of material and process parameters on the thermal conductivity of the polycrystalline material. The principal material is cubic boron nitride, a diamond analogue, which is well known for its high temperature stability, chemical inertness, and high thermal conductivity (1500 W/mK, single crystal). A basically amorphous material acts as the grain bonding phase. BN nanotubes participate in the densification of the overall structure. Characterization techniques will involve light and electron microscopy (SEM, ESEM, TEM) infrared and Raman spectroscopy, X-ray and electron diffraction, atomic force microscopy (AFM and related) and energy dispersive spectrometry (ESD).