Magnetostriction of stress annealed Fe-Ga-Al and Fe-Ga alloys under compressive and tensile stress

The addition of Al and Ga to b.c.c. alpha-Fe increases the magnetostriction of Fe in the [100] direction (a factor of 12 for Fe81Ga19). Fe-based magnetostrictive materials are machineable, mechanically tough and relatively inexpensive. They can be used with tensile loading and saturate in fields of only a few hundred Oe, even under compressive loads up to -100 MPa. The effects of annealing single crystal Fe86.9Ga4.1Al9.0 and Fe86.9Ga8.7Al4.4 and polycrystalline Fe81.6Ga18.4 rods under stress were examined. Stress annealing allows the material to achieve most of its strain without applying a prestress, simplifying device design. Most importantly, it allows the materials to operate magnetostrictively under a tensile load. Annealing was performed in a vacuum furnace with a -100 MPa stress for 10 minutes. The Fe-Ga-Al samples were annealed at 700degreesC and the Fe-Ga samples at 625degreesC. The magnetostriction was determined before and after stress annealing using compressive stresses of -0.7 MPa to -28 MPa for the Fe-Ga-Al samples and from -0 to -97 MPa for the Fe-Ga samples. One of the stress annealed Fe81.6Ga18.4 samples was measured under tensile stresses up to 34 MPa. After annealing, all samples showed full performance at near-zero stresses and tensile stress up to +20 MPa.