Formation of Metastable Phases and Their Effect on the Glass-Forming Ability of Cu-Hf Binary Alloys

Abstract

In this work, the glass-forming ability (GFA) of Cu-Hf binary alloys was systematically studied and some metastable phases were observed in the rapidly quenched samples. The microstructure of a Cu 50 Hf 50 as-cast rod between the surface and the central region was carefully examined, and the composition of the unknown metastable phase was identified to be about Cu 42 Hf 58 . The formation mechanism of metastable phases and their effect on the GFA of Cu-Hf binary alloys was also investigated. Taking the metastable phases into account, the parameter à was revised, and its prediction of the GFA of Cu-Hf binary alloys was found to be roughly in accordance with the experimental results.

Electronic structure and glass forming ability in early and late transition metal alloys

“…As seen in Fig. 3, and as found previously for Cu-Hf and Cu-Zr alloys [1], the variation of (Δχexp/χa) with Cu-content in Cu-Ti alloys agrees reasonably well with variations of dc [44] and γ * = ΔHamor/(ΔHinter-ΔHamor),where ΔHamor and ΔHinter are the formation enthalpies of glasses and intermetallic compounds [16], respectively, which reflect the GFA in these alloys [20,44]. In particular, |Δχexp/χa|, like γ * and dc, suggests the largest GFA around x = 60.…”

“…1 we show XRD patterns of selected Cu-Hf, Cu-Ti and Cu-Zr crystallized samples. As noted earlier [1,38], the crystallization of Cu-Hf MGs becomes more complex with increasing Cu content (which may contribute to the enhancement of GFA [17,20,21] observed at higher Cu-contents [1,16,37]). In particular, the XRD pattern of the Cu40Hf60 sample shows almost pure body centered tetragonal (bct) CuHf2 phase, whereas that of the Cu50Hf50 alloy already shows a complex mixture of bct CuHf2 and the orthorombic (o) Cu10Hf7 phase.…”

“…However, our γ * seems to underestimate the GFA of alloys around equiatomic composition and predicts maximum GFA close to x = 65. We note however that the variation of γ * with composition is very sensitive to which intermetallic compounds are included in calculation of γ * [16]. Thus the choice of intermetallic compounds from Cu-Hf system in [20] may have affected the agreement between γ * and dc , i.e.GFA, in Fig.…”

“…The correlation between the ES and GFA showed up best for Cu-Zr and NiZr2 alloys where direct data for the change in ES (ΔES) upon crystallization are available. The applicability of the Δχexp (ΔES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metalmetal MGs (including ternary and multicomponent bulk MGs) is briefly discussed.These empirical or semi-empirical criteria for high GFA are mostly based on thermodynamic parameters [3,4,9], characteristic temperatures (such as the reduced glass transition temperature Trg [13] and other similarly constructed parameters [14,15]), as well as enthalpies [16] and free energies or entropies [13,17]. The atomic size mismatch, which destabilizes the crystalline lattice [15,18] and the effective valence Zeff , which is expected to stabilize the amorphous phase [19], were also proposed to correlate with GFA.…”

Glass formation in the Ti–Cu system with and without Si additions

“…All equilibrium phases must be considered but a controversy still exists about the necessity to also include metastable phases in the calculations. Xia et al [35] have demonstrated that the consideration of the Cu 42-Hf 58 metastable phase in the calculation for the Cu-Hf system can improve the predictability of the c * criterion. On the other hand, the martensitic CuZr phase, which can be formed during rapid solidification [36], has not been considered in the c * and k+(Dh) 1/2 criteria calculations so far and the experimental results correspond well with the predictions for the Cu-Zr system [31,32].…”