Structure of Alnico V

The microstructure and crystal structure characteristics of Alnico V in various conditions of heat treatment have been determined by electron transmission microscopy and by electron and x-ray diffraction. The $a_0$ values of the different cubic phases have been determined from the electron diffraction data by using an MgO smoke film as an internal standard. In the water-quenched condition this material is a single-phase bcc, with $a_0\text{\hspace{0.17em}=\hspace{0.17em}2.84\hspace{0.17em}}\mathrm{A}$ . Transmission electron micrographs of the material in the magnetic field cooled condition show a structure appearing to be comprised of a matrix phase and oriented precipitate particles whose size is dependent on the cooling rate. Corresponding transmission diffraction patterns of such micrographed regions indicate that the matrix and precipitate are both part of the same crystallographic entity having the same crystal symmetry and, within experimental error, the same lattice parameter as the water quenched material. Diffraction patterns of slowly cooled specimens indicate the presence of small quantities of another constituent, bcc, $a_0\text{\hspace{0.17em}=\hspace{0.17em}2.62\hspace{0.17em}}\mathrm{A}$ . In the fully heat-treated (i.e., field cooled plus coercive aged) condition, the same microstructural appearance and lattice parameters, within experimental error, prevail, although magnetic tests show that a marked increase in anisotropy has occurred. Diffraction patterns from regions consisting exclusively of (deliberately induced) “gamma phase” indicate a randomly oriented, fine grained $\text{(5–6\hspace{0.17em}}\mathrm{grains}{\mathrm{/\mu }}^2)$ bcc structure $a_0\text{\hspace{0.17em}=\hspace{0.17em}2.84\hspace{0.17em}}\mathrm{A}$ .