Effect of ti content on the microstructure and high-temperature creep property of cast fe-ni-based alloys with high-al content

The cast Fe-Ni-based austenitic heat-resistant alloys with 4.5 wt% Al and varying Ti content were developed for high-temperature application. With increase in Ti content, strength of model alloys increased gradually at 700^◦C and 750^◦C. At 750^◦C, alloys with 35Ni–(2~4)Ti composition showed a significant increase in creep rupture life compared to 30Ni–1Ti alloy, attributed to the increase in γ’-Ni₃ (Al,Ti) precipitates due to higher Ni and Ti content. Among the 35Ni–(2~4)Ti alloys, increasing Ti content from 2 to 4 wt% gradually increased the creep rupture life in the as-cast condition. The creep rupture life was improved after solution annealing treatment, however, the beneficial effect of higher Ti content was not evident for 35Ni–(2~4)Ti alloys. After solution annealing, interdendritic phases were partially dissolved, but coarse B2-NiAl phases were formed. The size and amount of coarse B2-NiAl phases increased with Ti content. In the creep-tested specimens, creep void nucleation and crack propagation were observed along the coarse B2-NiAl phases, especially for high-Ti alloys. Therefore, the beneficial effect of the increase in γ’-Ni₃ (Al,Ti) precipitates for high-Ti alloys on creep property was limited due to the detrimental effect of the presence of coarse B2-NiAl phases.