The glass forming ability of Cu-rich Cu–Hf binary alloys

Abstract

We studied the glass forming ability (GFA) of Cu-rich Cu–Hf binary alloys and found that some of the alloys can be prepared as bulk metallic glasses with maximum diameter up to 2 mm by a conventional Cu-mould casting. The best glass former within the compositional range studied is off-eutectic Cu65Hf35 alloy, which is markedly different from the prediction from the multicomponent and deep eutectic rules. The GFA, thermal stability, kinetics of the glass transition and crystallization for Cu65Hf35 glassy rods were studied. The glass formation mechanism for binary Cu–Hf alloys was investigated from the thermodynamic point of view. It is suggested that the better GFA of off-eutectic Cu65Hf35 alloy could be due to its higher value of the parameter γ*, which is defined as the ratio between the driving force for glass formation and the resistance of glass formation to crystallization.

Thermodynamic Approach for Amorphous Alloys from Binary to Multicomponent Systems

“…The small difference in the experimental and predicted compositions was attributed to the fact that the entropy term was neglected in the calculations. Similar work on Cu-Hf alloys (Xia et al, 2006b) and Cu-Zr alloys (Xia et al, 2006c) have confirmed that this method is practical for predicting the best glass-forming compositions, at least in the studied binary alloy systems.…”

“…The predicted glass-forming composition range in the Ni-Ti system is 24 -77 at.% Ni, which is in well agreement with the experimental glass-forming composition range (28 -72 at.% Ni) prepared by mechanical alloying. Recently, by combining with a new glass-forming ability parameter, the Miedema's model has been used as a guide to searching for the best glass-forming ability composition in binary alloy systems (Xia et al, 2006a(Xia et al, , 2006b(Xia et al, , 2006c. It is argued that the formation of a metallic glass should involve two aspects (Xia et al, 2006a).…”

Study on crystallization kinetics of binary alloys through model colloidal mixtures

“…The size ratio (q) of small to large particles in the present binary colloid system is 0.69, which is quite similar to the atomic size ratio of Cu-Hf binary alloy (0.6971). It is interesting to find that there are two best glass-forming compositions reported up to now, Cu 55 Hf 45 [9] and Cu 65 Hf 35 [7,8] with the corresponding mixing ratios of 1.22 and 1.86, respectively. The agreement between the colloid mixtures results and the experiment data of binary bulk metallic glasses supports the present experimental design, and gives a direct evidence for the validity of topological factor in determining the glass-forming ability in binary metal liquid.…”

“…r small /r large Cu-Zr [10][11][12] 0.7039 Cu-Hf [7][8][9] 0.6971 Ni-Nb [13] 0.7525 Ca-Al [14] 0.6082 that q ranges from 0.55 to 0.80. Here, we use a binary colloid system to simulate the situation of binary BMGs with large particle (d = 2.9 m) and smaller particles (d = 2.0 m).…”

“…This compositional complexity makes it extremely difficult for different atoms to rearrange their spatial positions so that they are frozen directly into a disordered glassy structure upon cooling. Recently, binary BMG forming alloys have also been developed in a few alloy families [6][7][8][9][10][11][12][13][14], and their GFA is found to be very sensitive to the minor change of chemical composition [15,16]. These further confuse the criterions of GFA in metallic alloys.…”