The role of incoherent interface in evading strength-ductility trade-off dilemma of Ti_2AlN/TiAl composite: A combined in-situ TEM and atomistic simulations

摘要

The strength-ductility trade-off dilemma has inhibited the applications of many structural materials, TiAl alloys in particular. Here we report a new insight into the potential for increasing the ductility of Ti2AlN/TiAl composite without lowering its strength by tuning the interface with a unique incoherent atomic structure. The insitu TEM nanoindentation tests indicate that the Ti2AlN(10 (1) over bar3)//TiAl(111) incoherent interface micro-region possesses high compressive strength and good compressive ductility, because this incoherent interface can simultaneously play the role of softening and hardening in the process of compression due to the interfacedominated nucleation and annihilation of dislocations. The first-principles calculation and MD simulation results reveal that the reason why this incoherent interface displays a distinct compressive deformation behavior is that it has unique atomic structure, bonding character and interface-dislocation interactive mechanisms. By using first-principles calculations, it is found that this incoherent interface possesses a hierarchical atomic structure in the direction normal to the interface, the interface bonding characteristics are multiple and inhomogeneous depending on local atomic configurations, forming both the strong and weak interface interactive regions. The MD simulations indicate that the weakest interface interactive regions, i.e. incoherent regions in the Al2 atomic arrays of Ti2AlN(10 (1) over bar3) plane at the interface, could provide the preferred nucleation source for primary dislocations, incepting the plastic deformation. After the deformation achieves a certain extent, the local disordered interface regions generated by internal stress shearing could act as sinks to annihilating the secondary dislocations propagated from Al1 atomic layer of Ti2AlN(0001) plane, resulting in strain hardening.