Compositional Approach to Designing Fcc High-Entropy Alloys that Have an Enlarged Equiaxed Zone

2018 Metals  
A compositional approach to designing alloys that have an enlarged equiaxed zone is suggested in this study. The partitioning of elements during the solidification of CoCrFeMnNi high-entropy alloy (HEA) was confirmed through a directional solidification quenching experiment. Several HEAs were designed to maximize the effects of constitutional and thermal undercooling by considering factors including solute enrichment at the columnar front and the melting temperatures and thermal conductivities
more » ... mal conductivities of the individual elements. The newly designed HEAs were shown to have successfully enlarged equiaxed zones, and improved anisotropic properties. An equi-atomic CoCrFeMnNi HEA called Cantor alloy was prepared by pilot-scale VIM using high-purity elements. The details of pilot-scale casting (Y-block shape, 60 × 110 × 150 mm 3 ) are described in a previous report [7] . The HEA round bar (length: 100 mm, diameter: 4.8 mm) for the directional solidification quenching (DSQ) experiment was machined from the ingot. A DSQ experiment was carried out using a Bridgman-type directional solidification (DS) furnace. The specimen was heated to above its melting temperature. Afterwards, the temperature was lowered by the downward movement of the furnace with a thermal gradient. The solidification rate was 0.5 µm/s, and the specimen was quenched with liquid metal (Ga-In-Sn alloy) after 60 mm of growth. The details of the DSQ experiments are described in previous papers [11, 12] . The microstructures of the HEAs were analyzed using optical microscopy (OM) after mechanical polishing and etching with Kalling's solution. The chemical compositions of the DS specimens were characterized by an electron-probe micro-analyzer (EPMA, Cameca SX100, Gennevilliers, France) at the solid/liquid interface. The macrostructure and tensile properties of the newly designed HEAs were investigated in small-and pilot-scale vacuum induction melted castings. The cylinder-type tensile specimens (gauge length: 10 mm, gauge diameter: 2.5 mm) were prepared along three different loading directions on the pilot-scale Y-block ingot. These specimens were tested at a strain rate of 0.001 s −1 by a universal testing machine (model: Instron 5982, Norwood, MA, USA).
doi:10.3390/met8010054 fatcat:w362zmsqzbghblzw3dzk7tmzxe