Abstract:

In order to understand the effect of Ti on the carbides and topologically close-packed phases(TCP) in a high-temperature cast nickel-based superalloy, samples with different Ti content after heat treatment and different aging time were investigated by optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results show that the microstructures of as-heated alloy with different Ti content are the same and all are composed of γ, γ′, MC, and M23C6 carbides. With increasing Ti amount in the alloy, the volume fraction of carbides gradually increased. The carbide is mainly TaC when there is no Ti in the alloy, and the carbide gradually changes to (Ta,Ti)C with the addition of Ti. By examining the microstructures of alloys aged at 900 ℃ for different time, it has been found that the TCP phase segregated easily after addition of Ti in alloy. When the alloy with 2.7% mass fraction of Ti aged at 900 ℃ for 500 h, it shows that the σ phase contains a lot of Cr, W and Mo, indicating that it is necessary to control the amount of Ti in order to obtain an excellent phase stability of the alloy.

Key words: titanium, aging, carbide, TCP phase