Development of highly magnetostrictive iron-gallium and iron-gallium-aluminum alloys.

摘要

Magnetostrictive materials that exhibit high mechanical strength, good ductility, large magnetostriction at low saturation fields under both no-load and high-imposed loading conditions, and low cost are of great interest for use in numerous magnetomechanical sensors and actuators. The main purposes of this research are to (i) identify such alloys based on Fe and relatively inexpensive alloying elements, (ii) develop low cost processing of these alloys using directional solidification and thermomechanical processing, and (iii) develop an understanding of how alloying elements and crystal structures influence magnetostriction in Fe.; This work for the first time shows that BCC Fe-Ga based alloys show large low field magnetostriction. The magnetostriction values increase as Ga content increases and a preferred [001] crystallographic texture is approached. The values as high as 271 × 10−6 are obtained in the polycrystalline Fe-27.5 at.% Ga rod directionally grown at the rate of 22.5 mm/hour. These large values are obtained at very low applied fields (as low as 65 Oe) and with very small hysteresis. Alloys investigated here include Fe-x at.% Ga (x = 15, 20 and 27.5), Fe-y at.% Ga-(20-y) at.% Al (y = 0, 5, 10 and 15), Fe-13.75 at.% Ga-13.75 at.% Al, Fe-15 at.% Al, Fe-15 at.% Al-4 at.% Co, Fe-15 at.% Ga-4 at.% Co, Fe-15 at.% Mo, Fe-20 at.% Re, Fe-20 at.% Rh and Fe-10 at.% Sn.; A directional casting process involving solidification by rapid one-dimensional heat extraction produced rods with a weak [110] preferred orientation resulting in low magnetostriction. A directional growth process involving controlled crucible movement in a furnace down the temperature gradient resulted in rods with a preferred orientation approaching [001] direction and a large magnetostriction.; Orientation imaging microscopy study of texture evolution showed that a low-cost thermomechanical processing sequence of hot rolling, two-stage warm rolling reduction of about 60–65% with 900°C intermediate anneal, and a texture anneal at 1150°C can produce a [001] textured polycrystalline (Fe₈₅Ga₁₅)₉₉(NbC)₁ alloy. Rolled alloys exhibited tensile strengths of 576–588 MPa, yield strengths of 470–485 MPa and elongations of 28–29.5%.; Fe-Ga alloys possess an excellent combination of magnetostriction, magnetic and mechanical properties desirable in a magnetostrictive actuator/sensor material.