Some effects of composition on preparation of amorphous alloys

Abstract

In the preparation of amorphous alloy ribbons by the chill block casting technique, we have observed that some alloys are easily quenched to the amorphous state while others, similar in composition and similarly treated, may not be completely amorphous or may even be completely crystalline. These differences have been correlated with the constitution of the alloys used to prepare the amorphous ribbon. As an example, in the iron—boron system, the rangw over which completely amorphous ribbon may be made at cooling rates in excess of 10 6K/sec, extends from about 14% to 21% boron. Alloys with less or more boron consist of a higher melting temperature phase in conjunction with the eutectic matrix. The higher the temperature at which this phase forms on cooling the liquid, the more difficult it is to make a completely amorphous ribbon. Alloys of iron and phosphorus, when quenched, experience a marked undercooling; ribbons of this and similar composition are completely crystalline. Features of the ribbon indicate that it is formed in the amorphous state and subsequently reheated and crystallized. Examination of the crystallographic characteristics and cooling curves of the starting alloys, used to make the amorphous ribbons, enables one to predict the degree of amorphousness obtainable in most alloys.