Tensile deformation behavior of two Ti-based amorphous matrix composites containing ductile β dendrites

In this study, two Ti-based amorphous matrix composites containing Nb and Ta contents were fabricated by a vacuum arc melting method, and deformation mechanisms related to improvement of strength and ductility were investigated by observing the initiation and propagation of deformation bands, shear bands, or twins occurring at ductile dendrites and hard amorphous matrix. The two composites contained 60-66 vol.% of coarse dendrites sized by 42-73 mu m had excellent tensile properties of yield strength over 1 GPa and elongation over 5%. In the composite having higher Ta content, shear bands were formed first at the amorphous matrix, while dendrites were hardly deformed. With further deformation, dendrites were deformed in a band shape as a considerable number of twins were formed inside some dendrites. According to the EBSD analysis result of this composite, parts of beta phases were transformed to alpha phases during the tensile deformation, and twins were formed at phase-transformed a phases. In this composite mixed with a and beta phases, beta phases could play a role in interrupting the twin formation at alpha phases, which resulted in the increase in stress required for the twin formation and consequently the increase in yield and tensile strengths. (c) 2012 Elsevier B.V. All rights reserved.