High glass formability for Cu–Hf–Ti alloys with small additions of Y and Si

Abstract

The effects of small substitutions of Si and Y on the glass forming ability of a Cu 55 Hf 25 Ti 20 glassy alloy are reported and discussed. Fully glassy rods with diameters up to 7 mm and 6.5 mm, were produced for Cu 54.5 Hf 25 Ti 20 Si 0.5 and Cu 55-x Hf 25 Ti 20 Y 0.3 alloys, respectively. The addition of Si enlarged ∆T x (=T x-T g , where T g and T x are crystallisation and glass transition temperatures, respectively) considerably from 25 to 53 K for the Cu 54 Hf 25 Ti 20 Si 1 alloy. However, the results showed that the parameters obtained from thermal analysis, such as T rg , ∆T x and γ[=T x /(T g +T l)] are not reliably correlated with the glass forming ability (GFA), at least for these bulk glass forming alloys. The scavenging effects of the Y and Si, in particular the possibility of Y reducing the oxides, could be responsible for enhancing the GFA. It is proposed that the effectiveness of small additions of Si in enhancing the GFA may be the result of the possible formation of HfSiO 4 having a very large negative enthalpy of formation and, as a strong network former, it would form glassy particles which would be ineffective as nucleating agents.

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

“…12. As was discussed before, a similar optimum in GFA was obtained for other TiCu-based alloys with minor additions of Si in the range 0.5-1 at.% Si [7,17,18]. In addition, we have previously reported an optimum GFA with addition of 0.5 at.% Si to the quaternary alloy Ti 42.5 Cu 42.5 Zr 7.5 Ni 7.5 [18].…”

“…Additions of Si up to 1 at.% have been used to significantly improve the GFA of various TiCu-based alloys [7,17,18]. The reasons for this enhancement in GFA are still not completely understood but it has been associated with an increase of the short-ranging ordering [16], which results in more viscous/more densely packed liquids [19], and with a scavenging effect by the reduction of possible heterogeneous nucleation sites [17,20].…”

A study of mechanical homogeneity in as-cast bulk metallic glass by nanoindentation

“…The inability to generate larger sections is considered to originate from sensitivity to impurities acting as heterogeneous nucleation agents; the large negative enthalpy of formation of Ce 2 O 3 (−1823 kJ/mol [11]) will drive the reaction of Ce with dissolved oxygen, increasing the number density of nucleation sites, with these potentially acting to promote crystal formation and thereby reducing the glass forming ability of the alloy. Whilst the large negative enthalpy of formation of rare-earth oxides can act as oxygen scavengers when added in small amounts to base glass forming alloys, improving critical diameters [12], as Ce 70 Al 10 Cu 10 Ni 10 is the glass forming composition it may exhibit strong sensitivity to impurities with respect to glass formation. After casting, BMG rods were sectioned on a slow speed precision diamond cut-off saw and cold mounted in resin parallel to the cut surface for subsequent grinding and polishing, giving a high quality mirrored finish.…”

Glass Formation of Null-Matrix Cu-Hf-(Zr, Ti) Alloys

“…In addition, the glass formation and mechanical properties in the Cu-Zr-Hf-Ti, Cu-Zr-Ti and Cu-Hf-Ti systems for certain compositions were studied in detail 4,5 . On the other hand, it has been reported that additions of small amounts of B, Y and Si increased the GFA in these alloys 6,7 . Certainly, there is a compositional range in the Cu-Hf-Ti system in which BMG can be produced, thus, it is very important to propose a method for predicting the formation of BMG in specific compositions to facilitate the study of these materials.…”