Development of a drop-casting fixture to improve microstructure repeatability and data pedigree of arc cast alloy research

Abstract

Arc cast samples made for alloy development research using a conventional water-cooled copper hearth often exhibit columnar microstructures and some amount of unmelted material, the extent of which may vary from sample to sample or operator to operator. To increase consistency and in turn comparability across different samples and operators, a drop-casting fixture for a non-consumable electrode arc casting furnace was developed to provide repeatable solidification conditions. In comparing the use of the new fixture to a conventional hearth, pure molybdenum castings exhibited more equiaxed microstructures evidenced by circularity measurements of grain cross-sections improving from 0.51 ± 0.03 to 0.67 ± 0.004, and a set of Mo-MoRe alloys showing an average circularity of 0.75 ± 0.008, indicating that an additional benefit is more homogenous, isotropic samples. The equiaxed microstructure repeatability was verified across multiple molybdenum samples and multiple dilute MoRe alloys.