Local chemistry played an important role in determining the cohesive strength of grain boundaries in Ni3Al. Doping with B increased the room temperature ductility and changed the fracture mode from intergranular to transgranular, while doping with Zr increased the ductility but left the fracture mode predominantly intergranular. Electron energy loss spectroscopy and energy dispersive X-ray spectroscopy were used to probe the changes in local bonding (and hence the cohesive strength) produced by changes in local chemistry at large angle boundaries in Ni3Al. In addition, small angle tilt boundaries were studied to correlate structure with Ni-enrichment at the interface. B segregation to Ni-rich grain boundaries was shown to make the bonding similar to that of the bulk, thereby increasing their fracture resistance. The Ni-enrichment did not occur in the presence of Zr segregation to grain boundaries. Ni-enrichment to antiphase boundaries in small angle tilt boundaries lowered the antiphase boundary energy by reducing the number of high energy Al-Al interactions across the interface. Ni-enrichment to large angle boundaries was expected to produce a similar effect on energy.

Local Chemistry and the Cohesive Strength of Grain Boundaries in Ni3Al. Subramanian, S., Muller, D., Silox, J., Sass, S.L.: Acta Metallurgica Sinica A, 1995, 8[4-6], 309-18