2015 Volume 56 Issue 11 Pages 1834-1841
The successful fabrication of bulk metallic glasses (BMG) through suction casting based on the existing literature is a difficult task due to the sensitivity of glass-forming ability (GFA) to small changes in processing variables. We report processing challenges and process modifications required in the successful and consistent production of Zr-Cu-Al-Ni BMGs by arc melting and suction casting. Focus was placed on homogenization methods, elemental yields, and the effect of argon purge gas and Zr purity on GFA. A “cut and re-cast” homogenization method used to reduce oxidation produced good overall homogeneity but resulted in the entrainment of an oxide-rich surface layer into the bulk of the alloy. Homogenization by multiple melting iterations and prolonged melting times was ultimately found to be the most effective method. Zr loss was observed in the bulk of the samples post-production. This has been attributed to the formation of a Zr/ZrO2 surface layer during melting. Using X-ray diffraction and isochronal DSC, both argon gas purity and Zr purity were shown to markedly affect GFA. GFA was optimized within a specific oxygen concentration range. The highest GFA was obtained when using high purity argon (Grade 6.0) and low Zr purity (99.5%). The optimization of GFA in Zr-based BMGs at a critical oxygen concentration has not been shown in previous work.
