EFFECT OF 900-1150 DEGREES-C AGING ON THE MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF A DS CASTING NI3AL-BASE ALLOY IC6

The effect of high-temperature aging at 900-1150 degrees C on microstr ucture and mechanical properties of a recently developed directional-s olidification (DS) casting Ni3Al-base alloy has been studied in the pr esent investigation. The microstructure change during aging in the tem perature range 900-1150 degrees C for periods of 25 to 4400 h has been examined by optical microscope, SEM and TEM. The tensile and stress r upture properties of the specimens after aging at 900, 1000 and 1100 d egrees C for periods of 25 to 1000 h have been determined. The experim ental results showed that the mechanical properties slowly deteriorate d with aging time. The deterioration of properties was attributed to t he microstructure changes during aging, which include a volume fractio n decrement of the main strengthening phase gamma-Ni (Mo) solid soluti on due to the formation of gamma-Ni Mo phase by the reaction of gamma- ->Y-NiMo+gamma', the coalescence and growth of both gamma and gamma' p hase and a solution-hardening decrease due to the homogenization of Mo distribution in the gamma and gamma' phases.