Age-Hardened Gold Permalloy and Gold Perminvar
This work is an extension of previous work which showed that the addition of gold to Permalloy caused the precipitation of a gold-rich phase and thereby permitted the control of the coercive force by heat treatment. This addition of a second phase to Permalloy greatly improved the switching speed of the alloy. Some compositions of gold Permalloy had switching speeds four times faster than that of the standard composition. In the present work, some of the details of the precipitation process were studied. It was found that for some specimens annealed at 650°C, the precipitation of the gold-rich phase depended strongly upon cold working. When some alloys containing gold were quenched from the solution temperature and annealed at 650°C for 2 hr, there was little increase in coercivity and the electron micrographs showed practically no precipitation of particles of 1000-A diameter or larger. However, when the material was quenched from the solution temperature, drastically cold rolled and annealed at 650 °C, the coercivity was increased substantially and the electron micrographs revealed the presence of many particles having a diameter of 1000 A. Seven percent gold was also added to the Perminvar composition of 43% Ni-34% Fe-23% Co. The alloy behaved in a manner somewhat similar to the gold-Permalloy compositions. Age-hardening appeared in the vicinity of 600°C and square hysteresis loops were obtained. However, the threshold for rapid rotational flux reversal was substantially higher than the coercive force. Consequently, these alloys appeared less desirable for switching applications than Permalloy.