Microstructure and tensile properties of high-strength high-ductility Ti-based amorphous matrix composites containing ductile dendrites

Abstract

In the present study, two Ti-based amorphous matrix composites containing ductile dendrites dispersed in an amorphous matrix were fabricated by a vacuum arc melting method, and deformation mechanisms related to the improvement of strength and ductility were investigated by focusing on how ductile dendrites affected the initiation and propagation of deformation bands, shear bands or twins. Ti-based amorphous matrix composites contained 70-73 vol.% coarse dendrites of size 90-180 mu m, and had excellent tensile properties of the yield strength (1.2-1.3 GPa) and elongation (8-9%). The Ta-containing composite showed strain hardening after yielding, and reached fracture without showing necking, whereas necking occurred straight after yielding without strain hardening in the Nb-containing composite. The improved tensile elongation and strain hardening behavior was explained by the homogeneous distribution of dendrites large enough to form deformation bands or twins, the role of beta phases surrounding alpha phases to prevent the formation of twins, and deformation mechanisms such as strain-induced beta to alpha transformation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.