High glass formability for Cu-Hf-Ti alloys with small additions of Y and Si
Résumé
The effects of small substitutions of Si and Y on the glass forming ability of a CuHfTi glassy alloy are reported and discussed. Fully glassy rods with diameters up to 7 mm and 6.5 mm, were produced for CuHfTiSiand CuHfTiY alloys, respectively. The addition of Si enlarged ΔT (=T-T, where T and Tare crystallisation and glass transition temperatures, respectively) considerably from 25 to 53 K for the CuHfTiSi alloy. However, the results showed that the parameters obtained from thermal analysis, such as Tand ΔT 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 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.
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