Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites

摘要

A series of TiZr-based bulk metallic glass matrix composites (BMGMCs) with distinguished mechanical properties are successfully fabricated by adding different volume fractions of Ta (Ti38.8Zr28.8Cu6.2Be16.2Nb10 as the basic composition, denoted as Ta-0.0-Ta-8.0). Along with the growth of precipitated phase, typical dendritic morphology is fully developed in the TiZr-based BMGMCs of Ta-8.0. Energy-dispersive spectrometry analysis of the dendrites and glass matrix indicates that the metallic elements of Nb and Ta should preferentially form solid solution into dendrites. The chaotic structure of high-temperature precipitate phase is trapped down by the rapid cooling of the copper-mould. The detected lattice distortions in the dendrites are attributed to the strong solid solution strengthening of the metallic elements of Ti, Zr, Nb, and Ta. These lattice distortions increase the resistance of the dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Dendrites create a strong barrier for the shear band propagation and generate multiple shear bands after solid solution strengthening, thereby providing the TiZr-based BMGMCs with greatly improved capacity to sustain plastic deformation and resistance to brittle fracture. Thus, the TiZr-based BMGMCs possess distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta-0.5 possesses the largest plastic strain (epsilon(p)) at 20.3% and ultimate strength (sigma(max)) of 2613 MPa during compressive loading. In addition, the sample of Ta-0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680 MPa during the tensile process, and then progressively softens until it fractures at a strain of 10.2%. (C) 2014 Elsevier B.V. All rights reserved.