The evolution of η phase in Ni–Co base superalloys

The evolution of a η phase (Ni3Ti) in Ni–Co base superalloys with different Co and Ti content has been investigated. The results showed that the η phase existed in the samples with 23.1 wt.%Co and 5.4 wt.%Ti (TMW-3) and also the samples with 28.6 wt.% Co and 7.4 wt.%Ti (TMW-5) heat-treated at the temperature ranges of 1100–1140 °C, but not in the samples with 26.3 wt.%Co and 6.0 wt.%Ti (TMW-4). Even in TMW-3 and TMW-5, higher solution temperature (1180 °C) can fully reduce the formation of the η phase. The evolution of the η phase is complicated and may be related to the Ti content, Ti/Al ratio and alloy's composition.