Hot workability study of fine-grained iron-nickel based superalloys

P. A. Rosenthal, and B. London
Material Engineering Department
California Polytechnic State University
San Luis Obispo, CA.

D. Hardwick
Rockwell International Science Center
Thousand Oaks, CA.

Samples of two Fe-Ni based superalloys A-286 and RIM-D1 were compression tested at elevated temperatures using the Gleeble HAZ 1000 thermo-mechanical testing apparatus to simulate a forging operation. Samples were tested at temperatures of 1550, 1650 and 1700°F (843, 899, and 927°C) and at strain-rates of 0.05, 0.01, and 0.001s^-1 in order to determine their hot workability, or how the alloys deform as a function of temperature and strain-rate. In particular, the stability of the main strengthening precipitate g' (fcc, Ni₃(Ti,Al)) was explored, as this precipitate has a strong tendency to transform to the deleterious eta (h) (hcp, Ni₃Ti) phase either during processing, or while in service. g' is stable in the A-286 samples upon testing under these conditions, as no h was observed. However upon aging for 85 and 168 hours at 1480°F (805°C), h was observed but did not decrease the hardness of the samples. g' was less stable in the RIM-D1 samples as h formation was observed in all as-tested samples, forming primarily at the grain boundaries. In the RIM-D1 samples, the two samples tested at the lowest temperature (1550°F) and at 0.05 and 0.01s^-1 maintained their hardness (61 RA) as compared with the as-received sample (62 RA), while all other RIM-D1 samples in the test matrix (Table IV) showed a significant decrease in hardness upon testing (56 RA). Upon aging under the same conditions as the A-286 samples, the as-received and aged RIM-D1 samples showed a decrease in hardness (57 RA) compared to the as-received sample (61 RA), while the tested then aged RIM-D1 samples showed only a slight decrease in hardness (58.5 and 55 RA) as compared to the as-tested samples (61 and 56 RA respectively).