Enhanced mechanical properties of polycrystalline Cu-Al-Ni alloy through grain boundary orientation and composition control

By combined martensitic transformation calculation based on phenomenological theory and in-situ tensile tests, it was demonstrated that the mechanical properties of polycrystalline Cu-Ni-Al alloys can be enhanced by changing the stress state and improving the strength of grain boundaries. The experimental results indicated that, compared with ordinary hot-rolled Cu-Al-Ni alloys, controlled grain growth by continuous unidirectional solidification can change the stress state of grain boundaries and restrain intergranular cracks caused by local stress concentration, thereby making a significant tensile strain increase of 21.3% and superelasticity strain increase of 15.2%. Minor addition of B can enhance the bonding strength of grain boundary and reduce the formation possibility of intergranular cracks, resulting in a maximum tensile strain and superelasticity strain increase to be 3.1% and 2.0% respectively. These results would provide a theoretical and experimental foundation for enhancing mechanical properties of polycrystalline Cu-Al-Ni alloys by grain boundary control.