Phase Stability and Transformations in the Zr2Ni x Cu1−x Amorphous System

Abstract

Since Ni and Cu differ by only one valence electron, yet have nearly identical atomic sizes (1.27 vs 1.28 Å for Cu and Ni, respectively), the amorphous Zr 2 Ni x Cu 1-x system is ideal for isolating the effects of electronic structure on short-and medium-range order and the concomitant influence of both the structure and order on devitrification pathways. Thermal analysis, timeresolved high-energy X-ray diffraction (HEXRD), and transmission electron microscopy (TEM) were used to follow metastable and stable crystalline phase formation during devitrification. Using HEXRD, we observed that the first devitrification product in the Zr 2 Ni system is the C16 structure, if oxygen is kept sufficiently low, while the Zr 2 Cu system forms the C11b structure. For x = 0.25, the initial devitrification involves forming coexisting C11b and C16 phases. When Ni is increased to x ‡ 0.50, the initial devitrification only involves the C16 structure. These results are in complete accord with electronic structure calculations showing that the enthalpy of formation for the C11b phase is favored for x = 0, while enthalpies for C11b and C16 are nearly identical for x = 0.25; the C16 phase has the most negative enthalpy for all compositions in which x > 0.25.

Applications of an extended Miedema's model for ternary alloys

“…A more negative Zr-Ni interaction parameter should result in the enthalpy minimization routine favoring a relatively greater phase width for the c16 (Zr 2 Ni) structure as compared to the c11b (Zr 2 Cu) structure. This has already been verified experimentally by Kramer et al [45]. This indicates that at least in this system, the electronic structure plays an important role in GFA, a fact ignored in other parameterization schemes.…”

“…Experimental studies on crystallization behavior of Zr 2 Cu 1−x Ni x metallic glasses have shown that the Zr 2 Ni (c16) based phase crystallizes for x ≤ 0.625 [45,46]. In the range 0.625 ≤ x ≤ 0.375, both Zr 2 Cu and Zr 2 Ni based phases can be observed, while for x ≤ 0.375 Zr 2 Cu (c11b) is the preferred phase.…”

Short- and medium-range order in Zr80Pt20liquids

“…Studies of simpler Zr-based binary alloys have been more successful, providing important insights into the role of local atomic structures in dictating the transformation pathways and supercooling potential for a liquid. 11 It has been reported that Zr 80 Pt 20 can be quenched into the amorphous state by meltspinning 12,13 and that the X-ray diffraction patterns of the glassy ribbons show a pre-peak near 1.7 Å -1 . 14 Studies of Zr x Pt 100-x (73 ≤ x ≤ 77) glasses 15 show that the intensity of the pre-peak increases with increasing Pt concentration, suggesting that it arises from Pt-Pt correlations.…”

Structural evolution and thermophysical properties of ZrxNi100−x metallic liquids and glasses

“…These alloys also form the basis of more complex alloys with better GFA. Zr-Ni liquids and glasses have been extensively studied by X-ray [20][21][22][23][24] and neutron scattering [13,22,[25][26][27][28][29][30], as well as through simulations [21,[31][32][33]. The results from these studies have attracted attention because of the evidence for significant chemical ordering in both the liquid and glass [21,22,31,33].…”