Boron-induced microstructure evolution and mechanical properties of in situ Ti-based bulk metallic glass composites

The effect of boron(B) on the glass-forming ability (GFA), microstructure evolution and mechanical properties of (Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅)_100-xB_x bulk metallic glass composites (x = 0, 0.3, 0.5, 1.0 and 3.0 at. %) alloys was investigated. With increasing boron content to 0.3 at.%, the dendrite size is refiner than that of the other alloys, the B0.3 alloy presents good ductility and high strength at ambient temperature, which is mainly attributed to the strong interaction between dislocations, shear bands and the dendrite/glass interface. When the boron content is lower or higher than the critical value of 0.3 %, multiple slide steps decrease. Once the B content exceeds its maximum solid solubility, the phase instability of β-Ti dendrites and the glass matrix decreases, and more needle-like TiB₂ phases and irregular block-like ZrB₂ phases within and between the dendrites suppress the initiation of shear bands, resulting in brittle fracture.