Microstructure of a newly developed γ′ strengthened Co-base superalloy

The microstructure of a newly developed Co-base superalloy with enhanced high-temperature strength has been investigated using transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) techniques. It mainly consists of a typical γ/γ′ (FCC/L12) structure and a plate-shaped AB3-type (Ni,Co,Cr)3(Ti,Al)(Ni,Co,Cr)3(Ti,Al) intermetallic compound with hexagonal structure (a∼5.1 Å and c∼12.5 Å). γ′ is formed with a bimodal distribution and fine γ′ has a cuboidal morphology. Cr and Co are enriched in the γ phase, while Ti, Al and Ni are enriched in the γ′ phase. W and Mo are more or less uniformly distributed in both γ and γ′. Chemical composition analysis by 3DAP suggests that the plate-shaped phase has a higher Ti and lower Al content compared to that of γ′ phase, and the concentration of Ti, Co and Ni has a periodic variation along c-axis with a period of 12.5 Å in the plate-shaped phase.