Synthesis And Properties Of Ti-based Bulk Metallic Glasses And Ti-containing High-entropy Bulk Metallic Glasses

Owning to their excellent properties such as high strength and good corrosion resistance, Ti-based bulk metallic glasses（BMGs） are regarded as outstanding lightweight structural materials. However, the developed Ti-based BMGs exhibit relatively low glass-forming ability（GFA）, which limits their application prospect. Thus, it is of great importance to find out the key factors affecting the GFA of Ti-based BMGs, and then to develop the Ti-based alloys with large GFA.In this study, the GFA, thermal stability, and mechanical properties of the ternary Ti-Zr-Be BMGs have been improved obviously by Ag, Cu and Ni alloying. The developed quaternary Ti41Zr25Be34-x Agx, Ti41Zr25Be34-x Cux, Ti45Zr20Be35-x Cux, Ti41Zr25Be34-x Nix and Ti45Zr20Be35-x Nix alloys have relatively large GFA. Meanwhile, the critical diameter for forming fully amorphous structure of some Ti-Zr-Be-Ni alloys is raised to 20 mm, which is the largest size in the reported quaternary Ti-based BMGs to date. Moreover, the developed Ti50Zr16Be24Ni10 BMG possesses a high specific strength of 3.86 × 105 N·m/kg, and a large compressive plasticity of 5.7 ± 0.1 %, which is the first centimeter-scale BMG with Ti content more than 50 at. %. In addition, the effects of atomic size difference δ, electronegativity difference Δx and negative mixing enthalpy ΔHmi x on the GFA of all the developed and reported Ti-based BMGs have been investigated. The centimeter-scale Ti-based BMGs with large GFA have large atomic size differences（0.1176 ≤ δ ≤ 0.1333）, relatively large electronegativity differences（0.1194 ≤ Δx ≤ 0.1837） and more negative mixing enthalpies（-23.81 k J/mol ≤ ΔHmix ≤-33.15 k J/mol）. The above results could be served as an effective empirical rule in the alloy design for the newly Ti-based alloys with large GFA.The developed pseudo-quinary Ti-containing Ti₂₀Zr₂₀Hf₂₀Be₂₀（Cu20-x Nix） high entropy bulk metallic glasses（HE-BMGs） have large GFA, and their critical diameters for forming fully amorphous structure are all larger than 12 mm. In particular, the Ti₂₀Zr₂₀Hf₂₀Be₂₀（Cu7.5Ni12.5） alloy can be produced in BMGs with diameter up to 30 mm, which is the largest HE-BMG hitherto, and the Ti₂₀Zr₂₀Hf₂₀Be₂₀Ni20 alloy with the critical diameter of 15 mm, which has the largest GFA in the reported quinary HE-BMGs. The developed Ti-containing HE-BMGs have high yield strength and relatively large compressive plasticity. Meanwhile, the developed HE-BMGs with higher Ni content exhibit strong crystallization resistance and good thermal stability. Due to the high mi xing entropy and low Gibbs free energy difference, the Ti₂₀Zr₂₀Hf₂₀Be₂₀（Cu7.5Ni12.5） HE-BMG has the largest GFA in the developed Ti-containing HE-BMGs.