Processing of Materials in Strong Magnetic Fields: Phase Stability in FeCo-Based Alloys

1. Processing of Materials in Strong Magnetic Fields: Phase Stability in FeCo-Based Alloys Michael McHenry and David Laughlin Carnegie Mellon University: DMR-0406220 FeCo-based alloys are studied as a phase in nanocomposite magnets requiring large saturation inductions. Thermomagnetic processing (annealing materials in magnetic fields) can help to optimize the properties of these materials. The effectiveness of the processing treatment depends on the phases which are stable during processing. The various phases obtainable in FeCo-based alloys have different crystal structures, degrees of chemical order, and magnetic properties. It is well known that the stable phase depends on both the composition and temperature of the material. In magnetic systems phase equilibria also depends on the strength of the applied magnetic field.(Work of P. Ohodnicki, Y. Hanlumyung, M. E. McHenry and D. E. Laughlin, to be presented at the 2005 MMM Conf. - San Jose, CA) In our research, we attempt to quantify the effect of strong applied magnetic fields on the stability of the various phases in the FeCo system. The black solid lines of the phase diagram shown here were calculated from data and models available in the literature. These black solid lines are boundaries separating the various stable phases (g, a, and a’) as a function of temperature and composition of the alloys for zero applied fields. The colored lines correspond to calculated phase boundaries in the presence of strong applied magnetic fields. These boundaries indicate that, because the magnetic properties of the various phases are different, applied magnetic fields will tend to stabilize the phase which exhibits the largest magnetization. It is believed that this investigation will aid in the design of thermomagnetic processing schedules to obtain materials with desired technical magnetic properties.

2. Pittsburgh: A Meal of Steel and a Taste of Aluminum Michael McHenry and David Laughlin Carnegie Mellon University: DMR-0406220 Work of N. Hayward, M. E. McHenry and H. W. Paxton, to appear in the MRS Bulletin 30, September 2005. Nicole Hayward is beginning her junior year at CMU. While Materials Science and Engineering has had a rich and enduring impact on society, the field is not widely understood by the public. One method for improving public perception is to explain the historical role of materials as an economic driving force. In the U.S. there is perhaps no better example than the evolution of the steel industry. We have coupled with the Materials Research Bulletin to write a walking tour of Pittsburgh from a materials science view. The article highlights the historic and economic value of wrought metal structures such as the Alcoa building, Steel Tower, Smithfield Bridge, old Bessemer Converter, Monongahela Incline, an authentic copper brewery, and more. By walking an MRS tour, an average citizen can learn of a materials-related industrial and historical developments in a region. By pointing out the historical context of materials, we intend to emphasize the broader role of materials in societal evolution. The MRS Bulletin article will be reprinted for attendees of the MS&T Conference in Pittsburgh in Sept. 2005.