Structural changes in alnico alloys

The solid solution decomposition of Alnico 5 and Alnico 8 is studied by means of electron microscopy and X-rays. The following sequence of the decomposition process is found: Alnico 5: spherical zones-periodic modulated structure-rod-shaped particles of metastable tetragonal phases-final cubic phases; Alnico 8: the same sequence, but due to great importance of elastic energy at the decomposition, the three-dimensional modulated structure forms even during sharp quenching. The kinetics of modulated structure formation is studied. It is shown that the modulation wavelength increases according to a (time)ⁿlaw. The activation energies of the decomposition process are determined. The spinodal mechanism of decomposition of the alloys in question is discussed.