The Effects of Segregation on Grain Boundary Cohesive Energies in Ni3-xAIl+x 1L Najafahadi?,

The structure and properties of grain boundaries in the intermetallic alloy Ni3A1 have received considerable attention in the past several years due to their interesting mechanical properties. The aim in many of these studies [1-13] was to explain the increase in ductility that occurs when polycrystalline Ni3AI is doped with boron. Experimental observations [1-7] have shown that there is a strong correlation between nickel enrichment at grain boundaries and the ductilization of boron-doped polycrystalline Ni3AI. This grain boundary nickel enrichment has only been observed in Nirich Ni3-xAll+x (i.e., x<0). Some experimental studies have shown that grain boundary nickel enrichment also occurs in Ni-rich, boron-free polycrystalline Ni3-xAll+x [3,7]. Two models have been proposed [14,15] to explain the observed ductilization of polycrstalline Ni3AI. In the first model [e.g. 14], an increase in grain boundary cohesive energy has been attributed to nickel enrichment at the grain boundaries, while in the other model [15], it is suggested that the transmittal of slip across the grain boundary becomes easier in chemically disordered grain boundaries, where the disorder is induced by the nickel enrichment at grain boundaries. While these two purported effects of nickel segregation are not necessarily exclusive, experimental studies have been unable to conclusively validate either.