GLASS-TRANSITION BEHAVIOR OF FE-AL-B-SI AMORPHOUS-ALLOYS

Amorphous Fe-Al-B-Si alloys have been found to exhibit a glass transition phenomenon before crystallization. The composition range in which the glass transition is observed extends from 3 to 20%Al and 25 to 28%(B+Si) for Fe(100-x-2.8y)Al(x)B(y)Si1.8y, and 12 to 23%B and 7 to 16%Si for Fe(93-x-y)Al7B(x)Si(y). The glass transition temperature (T(g)) increases from 793 to 836 K with increasing B and Si contents and there is no distinct change in T(g) with Al content. The largest values of the temperature span DELTA-T(x) ( = T(x) - T(g)) between crystallization temperature (T(x)) and T(g) and the change in specific heat by the glass transition (DELTA-C(p,s) --> 1) are 36 K for Fe65Al10B16Si9 and 12.8 J /mol.K for Fe65Al7B18Si10. The appearance of T(g) for the Al-containing alloys implies an increase of the stability of the supercooled liquid against the precipitation of crystalline phases. The increase of the thermal stability is inferred to originate from the development of a more homogeneously mixed disordered structure through an optimization of the atomic size ratio resulting from the existence of Al with the largest atomic size.