Grain boundary cohesion and fracture in ordered intermetallics

Abstract

This paper reports that there is indirect experimental evidence (based on the unusual segregation behavior of boron), as well as direct theoretical evidence, to support the notion that increases GB cohesion in Ni{sub 3}Al. Whether that is enough to account for the dramatic ductilizing effect of boron is still unclear, although it is worth remembering that embrittling impurities can have similarly large effects on fracture mode and ductility (in the opposite direction) through changes principally in the interfacial energies. There is also indirect evidence (based on the lowering of the Hall-Petch slope by boron) to support the notion that boron facilitates slip transfer across GBs. However, as discussed in the text, there are factors other than the presence of boron which could affect the magnitude of the Hall-Petch slope, making its interpretation uncertain. Even if boron really does facilitate slip transfer, the details of exactly how this happens are still unclear. Of the two mechanisms suggested so gar, the one which suggests that boron facilitates slip transfer by increasing the mobility of GB dislocations appears to have been discounted recently by TEM experiments.