Effect of B Addition on the Extension of Supercooled Liquid Region in Zr–Cu–Al Base Amorphous Alloys

Abstract

The replacement of Al by B for Zr 65 Cu 27.5 A1 7.5 - x B x amorphous alloys was found to cause an extension of the supercooled liquid region before crystallization. The largest value of the supercooled liquid region(ΔT x ) defined by the difference between crystallization temperature (T x ) and glass transition temperature (T g ) is 100 K for Zr 65 Cu 27.5 B 4 Al 3.5 . The Δ T x value is much larger than that (72 K) for the Zr 65 Cu 27.5 Al 7.5 alloy. The increase is due to the significant increase in T x by the addition of B exceeding the degree of the increase in T g . The crystallization from the supercooled liquid takes place through a single exothermic reaction in the B concentration range less than 4 at%. The crystallized structure consists of Zr 2 Cu, Zr 2 Al and Zr 5 Al 3 for the Zr-Cu-Al alloy and changes into more multiple phases of Zr 2 Cu, Zr 2 Al, Zr 3 Al, Zr 5 Al 3 and ZrB 2 for the Zr 65 Cu 27.5 B 4 Al 3.5 alloy. Besides, the temperature dependence of the storage and loss moduli (E' and E) in the supercooled liquid also changes from the single stage for the Zr-Cu-Al alloy to the two stages for the Zr-Cu-Al-B alloy. The first-stage changes in the E'(T) and E(T) fit between both alloys and the second-stage change for the B-containing alloy takes place in the temperature range above T x of the Zr-Cu-Al ternary alloy. It is therefore concluded that the generation of Zr-B atomic pair with stronger bonding nature and longer relaxation time by the addition of B causes the increase in the thermal stability of supercooled liquid region through the retardation of the crystallization reaction. Furthermore, this is the first evidence on the synthesis of the amorphous alloy with the large Δ T x above 100 K for the Zr-Cu-B-Al alloy containing higher B content as compared with Al content.