GLASS-FORMING ABILITY OF ALLOYS

New amorphous alloys exhibiting a wide supercooled liquid region before crystallization were found to form by melt spinning in wide composition ranges of La-Al-M, Mg-Y-M and Zr-Al-M (M = Ni or Cu) systems consisting of the constituent elements with significantly different atomic sizes. The temperature span between glass transition temperature, T(g), and crystallization temperature, T(x), DELTAT(x) (= T(x) - T(g)) is > 50 K in the compositional ranges around La2AlM, Mg6Ln3M and Zr3AlM and the largest DELTAT(x) reaches 126 K. The critical cooling rate for the glass formation, R(c), is as low as 87-115 K/s and T(g)/T(m) is > 0.6 in the composition range where DELTAT(x) > 50 K. There is a clear tendency for R(c) to decrease with an increase of DELTAT(x) and T(g)/T(m). The crystallization of the alloys with large DELTAT(x) occurs through the simultaneous precipitation of several compounds. Based on these results, it is presumed that the large glass-forming ability for these alloys is due to a combined effect of the difficulty of long-range atomic redistribution required for the precipitation of the compounds, the rapid increase of viscosity with decreasing temperature and the large liquidus-solidus interfacial energy which originates from the optimally bonding and packing states resulting from large negative heat of mixing and large atomic size ratios.