Effect of interfaces of grain boundary Al2CuLi plates on fracture behavior of Al-3Cu-2Li

Transmission electron microscopy (TEM) and density functional theory (DFT) calculations were employed to investigate the interfacial characteristics and fracture behavior of Al-3Cu-2Li containing plate-like Al2CuLi (known as the T1 phase) precipitates at grain boundaries. TEM studies showed that T1 plates form at grain boundaries, with a coherent interface on one side parallel to the {1 1 1} planes of the matrix and a non-coherent interface with no preferred orientation relative to the grain on the other side. The low energy of the coherent interface leads to a serration of the grain boundaries due to the growth of the grain boundary T1 phase. Under tensile loading, the intergranular T1 phase leads to the formation of nanopores at the non-coherent side, and fracture mostly through the non-coherent grain boundary T1/matrix interface for under-, peak- and overaged conditions. DFT simulations showed that, under tensile loading, fracture is most likely to take place at the T1/Al interface, and the non-coherent side of the grain boundary is weakest as the decohesion energy is 25% lower than that of the coherent interface.