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

• The BMGCs contenting 1700 ppm and 2600 ppm oxygen exhibit more excellent mechanical properties than those without oxygen.
• The impurity elements in the β-Ti phase can induce solid-solution strengthening effect, which result in an enhanced strength.
• The hardened β-Zr phase and the brittle α-Ti crystals deteriorate the mechanical properties of BMGC with high oxygen level.

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 β-Ti → α-Ti, nor changes the microstructure of the Ti-BMG composites when the oxygen level is low. However, some tiny α-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 β-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 β-Zr phase, because of the excessive solid-solution hardening effect of oxygen, may lose the ability to arrest the shear bands. The brittle tiny α-Ti crystals can deteriorate the mechanical property of the composite.