THE EFFECTS OF BORON AND BERYLLIUM ON THE MICROSTRUCTURE OF RAPIDLY QUENCHED FE-PT ALLOYS

The effects of boron and beryllium on the microstructure of rapidly qu enched Fe-Pt alloy systems were investigated. A polytwinned structure derived from the nucleation and growth process with an order-to-disord er transformation is well revealed in annealed Fe60Pt40 alloy ribbons. Polytwinned clusters embedded in the dominant ordered tetragonal gamm a(1) matrix (granular shape) of the as-quenched Fe50Pt50 and (Fe0.6Pt0 .4)(100-x)B-x alloy ribbons are observed in samples with x greater tha n or equal to 6. The FeB precipitates cause an increase in the Pt cont ent of the ordered gamma(1) matrix in the ternary alloys, and act as p inning sites retarding the growth of matrix grains in both the as-quen ched and annealed states. The result is that the high-temperature gamm a phase is difficult to obtain in the as-quenched state and the grain size of the gamma(1) matrix decreases. The shape of the FeB precipitat es changes from planar to columnar with increasing boron content. The formation of the BePt phase observed on the grain boundaries of the di sordered gamma phase in the as-quenched state causes the difficulty in formation of the ordered gamma(1) phase during the annealing process. Grain size refinement in the Fe-Pt-Be system is weaker than in the Fe -Pt-B system. Moire fringes are observed in both binary and ternary al loys.