Microstructures of a Ni-9.6 at.% Ta-16.6 at.% Cr alloy after aging up to 1000 hours from 600 to 1,000°C

The effects of aging of a Ni-rich Ni-Ta-Cr alloy on the microstructure (using optical and scanning electron microscopy) and hardness are presented. In the solution-annealed condition (1280°C, 4 h) the microstructure consisted of a face-centered cubic matrix and about 10% of a Ni₃Ta type phase, which contained some Cr; the hardness was about 530 DPH. No change in the microstructure nor significant change in hardness occurred upon aging at 600°C for 1,000 h. Aging from 700 to 1000°C produced a significant decrease in hardness, to about 330 DPH after 1000 h. A lamellar product formed, usually initiating at the secondary particles present in the solution-annealed condition. At longer times and higher temperatures, a coarser lamellar product formed. The results of qualitative EDS analysis of the phases are reported.