Effect of additional elements (M) on the thermal stability of supercooled liquid in Fe(72-x)Al(5)Ga(2)P(11)C(6)B(4)M(x) glassy alloys

The dissolution of 2 at%Nb, 5%Mo, 4%Cr or 6%Co for the Fe(72-x)Al(5)Ga(2)P(11)C(6)B(4)M(x) glassy alloys was found to be effective for the extension of the supercooled liquid region defined by the difference in the glass transition temperature (T-g) and crystallization temperature (T-x), Delta T-x(=T-x-T-g). The Delta T-x, value is 60 K for the Fe-Al-Ga-P-C-B alloy and increases to 66 K for M=2%Nb, 62 K for 4%Mo, 61 K for 4%Cr or 6%Co. The increase in Delta T-x is due to the increase in T-x exceeding the degree in the increase in T-g. The crystallization of the glassy alloys with Delta T-x above 60 K takes place through a single stage of amorphous (Am)-alpha-Fe+Fe3P+Fe3C+Fe3B and no appreciable change in the crystallized structure with M elements is seen. On the other hand, the addition of 2%Cu or 2%Ni causes the disappearance of the glass transition phenomenon before crystallization, accompanying the change in the crystallization process to the two stages of Am-->Am'+alpha-Fe-->alpha-Fe+Fe3P+Fe3C+Fe3B. It is therefore concluded that the appearance of the wide supercooled liquid region is due to the retardation of crystallization resulting from the redistribution of the constituent elements on a long range scale which is required for the simultaneous precipitation of the four crystalline phases. The effectiveness of additional Nb, Mo or Cr element is presumably because the redistribution of the constituent elements leading to the crystallization becomes difficult.