High tensile ductility of Ti-based amorphous matrix composites modified from conventional Ti-6Al-4V titanium alloy

Three Ti-based amorphous matrix composites containing ductile dendrites were fabricated by adding alloying elements of Ti, Zr, V, Ni, Al and Be into a conventional Ti-6Al-4V alloy, and the deformation mechanisms related to the improvement of tensile ductility were investigated by focusing on how the effective size of ductile dendrites affected the initiation and propagation of deformation bands or shear bands. The composites contained ∼73-76 vol.% dendrites ∼63-103 μm in size, and had excellent tensile properties with a yield strength of over 1.3 GPa and an elongation of over 7%. In the composite containing very large dendrites, deformation bands were formed at dendrites in the same direction. In the composite containing small dendrites, however, many deformation bands were actively formed inside dendrites in the several directions, and cross each other to form widely deformed areas. This wide and homogeneous deformation in both dendrites and amorphous matrix enhances the tensile ductility, resulting in high strength and elongation occurring simultaneously. In order to theoretically explain the enhanced tensile ductility, a finite-element method (FEM) analysis based on the real microstructures considering dendrite crystal orientations was performed. The FEM simulation results of deformation bands or shear bands were in good agreement with the experimental findings. The reasons for such a good match between the simulation and experimental results are discussed in detail.