The influence of three different ageing treatments (R1: 1100C/2h, air cooling+870C/32h, air cooling, R2: 870C/32h, air cooling and R3: 1060C/2h, air cooling+870C/32h, air cooling) upon the stress rupture properties of Ni3Al-base single-crystal alloy IC21 was investigated. The results indicate that ageing heat treatments have obvious effects on stress rupture properties of IC21 at 850C and 500MPa. After R3 ageing treatment, IC21 alloy exhibited the longest rupture life and the smallest ellipticity and elongation compared to those after the other two ageing treatments. Microstructure examination shows that the mean size of γ′ precipitate was about 0.44μm after R3 ageing heat treatment (1060C/2h, ac + 870C/32h, ac). Transmission electron microscopic study on the rupture samples illustrates that after R1 and R2 ageing heat treatments, the density of stacking faults increases and the length was larger compared to that after R3 heat treatment. Meanwhile the shearing of γ′ precipitates were more severe. The appropriate γ′ phase size and γ channel width after R3 treatment promote homogenous deformation by <110>{111} slip in the matrix, and facilitate the formation of finer dislocation networks on the γ/γ′ interface, which could restrain the shearing of γ′ phase by dislocations.

Influence of Ageing Treatments on Stress Rupture Properties of Ni3Al-Base Single-Crystal Alloy IC21 at 850°C. Li, H., Li, F., Li, S., Zhang, H., Gong, S.: Materials Science Forum, 2013, 747-748, 659-64