HETEROGENEOUS NUCLEATION OF DELTA' ON DISLOCATIONS IN A DILUTE ALUMINUM-LITHIUM ALLOY

The nucleation of delta' on dislocations with small undercooling in bi nary aluminum-lithium alloys has been examined. The study of related m icrostructures was performed using transmission electron microscopy (T EM), which demonstrates that delta' preferentially nucleates on disloc ations with a strong edge character and locates at the side where the stress field is compressive without destroying the dislocation core st ructure. This qualitatively justifies the theoretical prediction by La rche on coherent heterogeneous nucleation on edge dislocations. Follow ing the evaluation of the volume free energy change for the binary sys tem by the ideal solution model and the mean-field model by Khachatury an, the nucleation barrier and the nucleation rate were calculated and compared with experimentally determined data based on Larche's model. Specifically, the back-calculated interfacial energies from the exper imentally determined nucleation rate data are in good agreement with t he interfacial energy temperature dependence predicted by the related interfacial energy model. The effects of misfit strain, volume diffusi on, interfacial energy, and nucleation sites are discussed.