Enhanced mechanical properties of Ti-based metallic glass composites prepared under medium vacuum system

The Ti48Zr20Nb12Cu5Be15 bulk metallic glass composites were prepared by copper mold casting under medium vacuum conditions (0.15 Pa-25 Pa). The addition of impurity elements neither induces the phase transformation of beta-Ti -> alpha-Ti, nor changes the microstructure of the Ti-BMG composites when the oxygen level is low. However, some tiny alpha-Ti crystals separate out from the interface between the dendritic second phases and glassy matrix when the oxygen content is 7500 ppm. The impurity elements concentrated in the BMGs lead to a sharp decrease of GFA when the average oxygen level is above 4500 ppm. The impurity elements absorbed in the beta-Ti phase can induce a significant solid-solution strengthening effect, which results in an enhanced strength. With the average oxygen level further increases, the higher shear modulus and hardness of beta-Zr phase, because of the excessive solid-solution hardening effect of oxygen, may lose the ability to arrest the shear bands. The brittle tiny a-Ti crystals can deteriorate the mechanical property of the composite. (C) 2015 Elsevier B.V. All rights reserved.