Possibility for As-Cast Application for Cold Crucible Levitation Melted Co-Ni-Al Alloys with <i>γ</i>+<i>β</i> Dual Phases, and Their Mechanical and Oxidation Properties

Nine Co-Ni-Al alloys with the γ+β dual phases were designed by varying two electronic alloying parameters, Bot and Mdt, and the ingots were prepared by cold crucible melting. The phase boundaries of the γ, β, and γ+β regions in the Co-Ni-Al system were specified using the Bot-Mdt diagram. The microstructures of the nine Co-Ni-Al alloys consisted of primary γ or β phases and the eutectic of γ+β, and their volume fractions and phase stabilities were evaluated on the basis of the Bot-Mdt diagrams. The as-cast application possibility of Co-40Ni-28Al could be suggested in the view of the tensile and hardness properties as macro properties, and the segregation degree of solute elements as micro one. Similar tensile behaviors were shown on the as-cast experimental alloys with similar microstructural characteristics. The Hv and Young's modulus values depended on the mass ratios and degree solid solution strengthening in both the γ and β phases, which resulted from the Bot and Mdt values. The maximum n value and minimum yield ratio were observed for both the Co-23Ni-23Al and Co-23Ni-18Al alloys, which indicated an inverse relationship between the Hv or Young's modulus behavior and n or yield ratio behavior. Their alloys consisting of γ or β, and eutectic γ+β were on the equivalent vector of Ni and Al in the Bot-Mdt diagram. The oxidation curves consisted of an initial acceleration stage followed by a subsequent arrest stage, and similar oxidation behavior was observed for all experimental alloys. The high-performance Co-Ni-Al alloys with the γ+β dual phases can thus be designed within the Bot-Mdt diagram, which can be used to predict phase stability, mechanical and oxidation properties.