EFFECTS OF STRAIN-RATE AND TEMPERATURE ON DEFORMATION-BEHAVIOR OF IN 718 DURING HIGH-TEMPERATURE DEFORMATION

The hot deformation characteristics of a wrought IN 718 alloy were investigated by compression testing at constant strain rates in the range of 0.1 to 5 x 10(-3) s-1, and testing temperatures in the range of 950 to 1100-degrees-C using a 200 ton capacity microprocessor controlled Fielding hydraulic press. Examination of the microstructures was carried out by optical microscopy and TEM. The flow stress of the compression tests showed a single peak in the flow stress-strain curves, and indicated that a dynamic recrystallization transition took place during the hot compression. The relationship between the peak stresses (sigma(p)) and the Zener-Hollomon parameter (z) can be expressed by sigma(p) = 0.5Z0.17. ''Necklace'' microstructures were observed at testing temperatures below 1050-degrees-C, for strain of 0.7. The fraction of recrystallized grains increased with the increasing temperature and strain, and decreasing strain rate. Fully recrystallized microstructures were observed at temperatures 1050-degrees-C or greater, with a strain of 0.7.