MECHANISMS OF HIGH-TEMPERATURE CRACK-GROWTH IN NICKEL ALUMINIDE

Nickel aluminides, based on Ni3Al, exhibit high strength at elevated temperature. However, they may be prone to low ductility intergranular crack growth in the presence of oxygen. It has been found empirically that the presence of chromium improves high temperature tensile ductility. A detailed study of oxidation and crack growth mechanisms in the absence of chromium has provided evidence to suggest that fracture is controlled by the internal diffusion of oxygen along grain boundaries in front of the crack tip. The current work considers the effect of chromium on crack growth and oxidation at crack tips in nickel aluminide. Some of the major results of a more extensive study are summarised, showing crack growth rates as a function of stress intensity and temperature, together with characterisation of the role of chromium in microstructure and crack tip oxidation, using a variety of analytical techniques. © 1990 Maney Publishing.