On the microstructural evolution and partitioning behavior of L12-structured γ′-based Co-Ti-W alloys upon Cr and Al alloying. (January 2019) - Yoo, Boryung
Abstract: We report on the effects of Cr and Al on the microstructure and elemental partitioning behavior of γ/γ′ forming Co-Ti-W-based alloys. Additions of Cr to a Co-15Ti-3W (at.%) base alloy at the expense of Ti led to a decrease in γ′ volume fraction, whereas Al additions at the expense of Co led to substantially increased γ′ volume fractions. Such alloy modifications resulted in reduced γ/γ′ lattice misfits. Using atom probe tomography, we could show that Ti and W strongly partitioned to the γ′ phase, whereas Al and Cr partitioned to γ. While Cr appeared to have only minor effects on the partitioning behavior of the other alloying elements, Al enhanced partitioning of Ti and in particular W to γ′, thus causing the observed increases in γ′ volume fraction. Highlights: A two-phase γ/γ′ microstructure was observed for Cr and Al-added Co-Ti-W-based alloys. W was found to partition to γ′, reducing the γ/γ′ lattice misfit and increasing the γ′ volume fraction and solvus temperature as compared to the previously reported Co-Ti alloy. Cr and Al additions caused further reduction of the γ/γ′ lattice misfit and increases in γ′ volume fraction and solvus temperature. Al enhances partitioning of Ti and in particular W to γ′.