High Temperature Magnetic Materials (278)
A national initiative, led by the Air Force Research Laboratory, Propulsion Directorate (AFRL/PR), is underway to develop and test a More Electric Aircraft (MEA). One particular design challenge involves the structural integrity of the rotating turbomachinery that may operate at stress levels in excess of 600 MPa at temperatures ~600°C.
The University of Dayton Research Institute has developed a process to produce soft magnetic materials for high temperature applications in the greater or equal to 600°C range. This process presents the theoretical as well as practical challenge of enhancing the high temperature mechanical performance without degrading the magnetic properties. The fundamental concept of this invention is that at temperatures greater than the transition temperature (Ttr), large-grain material is mechanically superior to small-grain material. For Fe-Co-V alloys, Ttr is lower than the operating temperature of advanced power components, and large-grain material is mechanically superior.
The basic concept of the approach described in this invention is to minimize grain boundary sliding at high temperatures (>Ttr) by significantly reducing the volume of grain boundaries in the Fe-Co-V alloy through grain coarsening. In a commercial Fe-Co-V alloy sheet, the average grain size is 2-3 µm. It is generally believed that obtaining grains larger than the thickness of the sheet is difficult in the sheet form of a material. However, by applying the very simple process proposed by this invention, it is possible to increase the grain size of the Fe-Co-V alloy to the range of millimeters or even centimeters. Thus, the volume of grain boundaries can be reduced by a factor of 106 to 109. Therefore, the creep resistance of an Fe-Co-V alloy sheet can be significantly improved. In addition, because grain boundaries, like any other crystal defects, impede domain wall movement, reducing the volume of grain boundaries will increase permeability and reduce coercivity and hysteresis loss of the Fe-Co-V alloy. Thus, this approach will simultaneously improve mechanical and magnetic properties.
U.S. Patent Application 09/476,664 filed January 3, 2000.
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