Abstract
Alnico 8-type alloys containing more than 5%Ti has been found to have very high coercive forces, particularly when the isothermal magnetic treatment is applied. In order to explore its cause, in this work the transformations, microstructures and magnetic properties were investigated on the specimens of Alnico 8-type alloys with various titanium contents. The critical temperatures of the transformations in solid state were determined as a function of titanium content. It may be reasonably concluded that a mechanism of magnetic hardening in the alloys is similar to that in Alnico 5-type alloys containing no titanium.It was shown that the coercive force of the alloys depends largely upon the temperature of the isothermal treatment, and slightly upon the treating time. For each specimen, the optimal temperature of the treatment was found to be about 50°C below the critical temperature of the immiscibility gap reaction, and it is lowered with increasing titanium content. In addition the magnetic anisotropy induced by the isothermal treatment in a magnetic field seems to decrease in magnitude with increasing titanium content. Furthermore, the electron-microscopic observation has revealed that the precipitate particles developed by the optimal treatment are likely to increase in both size and dimension ratio with increasing titanium content.
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