Enhancing magnetic properties of amorphous alloys by annealing under stress

#This invention relates to amorphous metallic alloys. More particularly, it relates to the enhancement of the magnetic properties of amorphous metallic alloys.

#Amorphous metallic alloys, also sometimes referred to as "glassy metals", result when certain component materials are quenched from the molten state to the solid state at extremely high rates. For example, quenching at the rate of 10.sup.5 degrees per second has been found to result in an alloy which is substantially homogeneous and amorphous in form. That is, the rapid cooling prevents formation of a crystalline structure in the alloy material.

#Until rather recently, the only known technology for the production of amorphous alloys utilized techniques such as vacuum evaporation, sputtering, electrodeposition, and the like. Also, the materials produced by those processes were not of convenient size or shape for extensive further development for some purposes, and any attempts to alter the shape destroyed their amorphous, homogeneous character.

#FIG. 1 shows a plot of remanence versus load for the example set forth hereinafter;

#FIG. 2 shows a plot of coercive field versus load for the example set forth hereinafter; and

#FIG. 3 shows exemplary hysteresis loops for the example set forth hereinafter.

#A ribbon shaped amorphous alloy sample 10cm long by 1.5mm wide by 35 micrometers thick, composed of nickel, 40 atomic percent; iron, 40 atomic percent; phosphorous, 14 atomic percent; and boron, 6 atomic percent; was placed under a tensile stress of 36 kilograms per square millimeter. The stressed amorphous alloy material was elevated to a temperature of 200.degree. C. in air, and held at that temperature for two hours. Thereupon, the heat was removed and the sample was cooled, and the stress was then removed.

#FIG. 1 depicts the effect of remanence on the sample annealed as set forth above, as compared with the remanence as a function of stess for the same sample prior to the annealing process. Remanence is set forth on the ordinate as a fraction of saturation magnetization, and load is depicted on the abscissa in kilograms per square millimeter. Most noteworthy, the annealing process is seen to have the effect of conferring residual enhanced mangetization upon the amorphous alloy sample. Whereas in the unloaded state, the material prior to annealing had a remanence of 35%, the remanence after annealing has been improved to 70%, which is equivalent to the remanence of the material prior to annealing under approximately a four kilogram per square millimeter load. Thereupon, as the annealed alloy sample is loaded, the remanence further increases, reaching a value of 94% at approximately 6 kilograms per square millimeter loading. The remanence of the annealed product thereupon asymptotically approaches the same limiting value as it did prior to annealing.

#In FIG. 2, the variation of coercive field with load of the annealed product is compared with its same characteristics prior to annealing. Coercive field is plotted on the ordinate in Oersteds and load is plotted on the abscissa in kilograms per square millimeter. Annealing may be seen to reduce the unloaded coercivity from 0.065 to approximately 0.058. Thereupon, subsequent loading further lowers the coercivity, down to a minimum of approximately 0.025, beyond which the coercivity remains fairly constant. From FIG. 2, it may be seen that not only is the attainable coercivity lower for the annealed samples than for the same samples prior to annealing, but furthermore the range in which the greatest change in coercive field occurs is considerably compressed. That is, for the annealed sample, the substantial reduction in coercive field occurs between no load and a load of 6 kilograms per square millimeter, whereas for the same sample prior to annealing, the entire reduction occurs over a much broader load range.