beta-type Ti-based bulk metallic glass composites with tailored structural metastability

摘要

Bulk metallic glass composites (BMGCs) containing an in-situ formed metastable beta phase (beta-type BMGCs) being capable of transforming to martensites, are a promising class of alloys. Nonetheless, the influence of the structural metastability of b phases on the deformation mechanisms of BMGCs remains largely unclear. This, however, is crucial for understanding and optimizing plastic deformability. In this study, three Ti-based beta-type BMGCs with nominal compositions of (Ti0.505Zr0.353Fe0.028Be0.114)(100-x)Cu-x (x = 1, 5, 8) have been developed, in each of which the beta-Ti phase has a different metastability. For x = 8, the b phase precipitates exclusively and does not transform martensitically during deformation. At the lowest Cu content (x = 1), however, the b phase contains a high density of fine u phase upon quenching, which hinders the deformation-induced martensitic transformation. b phases in both BMGCs deform plastically by dislocation glide. Only when x = 5 does the b phase undergo the martensitic transformation to alpha ''-Ti due to an appropriate degree of metastability. The reversible phase transformation between b and alpha '' followed by twinning in alpha '' on continuing deformation leads to a "double yielding" behavior and results in strong work-hardening capability as well as superelasticity during compression (cyclic loading) tests. (C) 2017 Elsevier B.V. All rights reserved.