COMPOSITE MAGNETOSTRICTIVE MATERIALS FOR ADVANCED AUTOMOTIVE MAGNETOMECHANICAL SENSORS

摘要

Metal-bonded Co-ferrite composites have been fabricated. These have a combination of saturation magnetostriction in excess of 200 ppm and coercivity of about 8kA/m, which together give a high initial piezomagnetic coefficient, (partial derivλ/partial derivH)_σ of 1.3 x 10~(-9) A~(-1)m. This is comparable to polycrystalline Terfenol, and much larger than Terfenol-based composites consisting of 30 vol% Terfenol and 70vol% NaPO_3, which had (partial derivλ/partial derivH)_σ values of typically 2 x 10~(-10) A~(-1)m. The magnetomechanical effect under torsional stress measured at room temperature shows that the changes of surface axial magnetic field in response to applied torque were as large as 65 AN~(-1)m~(-2), with only a small hysteresis of +- 0.5 N·m. In addition, the metal-bonded composites are mechanically robust, corrosion-resistant, and can be brazed to shafts. Metal-bonded Co-ferrite composites therefore appear to be prime candidates for practical magnetomechanical torque sensors in the range of +-10 N·m, and for other magnetomechanical sensing and actuating applications. The temperature dependence of the magneto-mechanical effect under torsional strain in metal-bonded Co ferrite composite was investigated. The sensitivity changed from 78 AN~(-1)m~(-2) at -37℃ to 34.2 AN~(-1)m~(-2) at 90℃ while the magnetomechanical hysteresis decreased from +-1.8 N·m at -37℃ to negligible abc ve 60℃. The effects of temperature on magnetomechanical effect under torque at remanence can be described in terms of four processes: changing magnetostriction, changing anisotropy, changing spontaneous magnetization and releasing the pinning sites o domain walls. Metal-bonded Co ferrite composites show capacity for linear magnetomechanical response to torque which can be achieved by changing the temperature dependence of anisotropy through the use of metallic additives. These materials have been shown to have sufficient magnetoelastic response (specifically the dynamic range of response that is available as a result of it having greater than 200 ppm magnetotostriction, and the large strait derivative in excess of 1 x 10~(-9) A~(-1).m) for certain types of torque sensors and other nagnetostrictive sensing and actuating applications. In addition, the materials have adequate mechanical properties (fracture strength > 69MPa) and corrosion resistance for the application. However, little was known about the temperature dependence of the magnetomechanical response in these materials.