Crystallization behavior of ternary γ–γ′ Co–Al–W alloy

In the investigation, crystallization behavior of ternary γ – γ ′ alloy based on Co–Al–W system was analyzed. The alloy with nominal composition Co–9Al–9W (at.%) was prepared via vacuum induction melting. Solidification characteristics of the investigated superalloy were obtained by a method of thermal analysis based on temperature measurement of metal solidifying in a mold. After casting, obtained metallic materials were investigated by differential thermal analysis in order to determine characteristic temperatures and compare results with those of obtained in the first thermal analysis. Furthermore, a description of primary microstructure was performed for ingots solidified with two different cooling rates. The analysis was made using X-ray diffraction, optical microscopy and scanning electron microscopy. The crystallization path of alloy was investigated. The solidification range of alloy was narrow. The crystallization in a sand mold resulted in the dendritic microstructure containing γ single phase. The as-cast microstructure after solidification with higher cooling rate was comparable; however, observed crystals were mostly columnar, while sand cast was characterized by equiaxed crystals structure.