Modulating the microstructure and mechanical properties of β-Ti-reinforced bulk metallic glass composites by carbon addition

The effects of carbon addition on the microstructure modifications and mechanical response of Ti48Zr20Nb12-Cu5Be15 BMGCs are investigated. With increasing carbon content from 0.1 at.% to 0.3 at.%, the evolution of morphology and solid solution strength is not obvious, and the ductile-brittle transition is presented due to the large changes of the sub-Tg relaxation enthalpies, Delta H-rel, in the glass matrix when the interstitial C content increasing to 0.5 at. %. Once the C content excess this threshold value, a large melting area and open cracks are mainly related with the size and number of carbide particles and the magnitudes of free volume in the glass matrix, which indicates the appearance of large-sized vermicular-like structure is the cause of instability of composite material. In addition, when C exceeds its limit solute concentration, harder beta-Ti-reinforced dendrites and precipitate phases can suppress the initiation of shear bands, and the transfer ability of the concentrated stress to the surrounding glass becomes weaker, which promotes the formation of cracks, resulting in brittle failure.