Effects of Zr and Si on the Glass Forming Ability and Compressive Properties of Ti-Cu-Co-Sn Alloys

To succeed in finding novel Ti-based bulk metallic glasses, which are free from Be, Ni, and noble metallic elements, a comprehensive study was performed on the effects of Zr and Si on the microstructural evolution, glass-forming ability (GFA), and mechanical properties of Ti₄₆Cu_44−x Zr _x Co₇Sn₃ (x = 0, 5, 10, 12.5, and 16 at. pct) and Ti₄₆Cu_31.5Zr_12.5−x Co₇Sn₃Si _x (x = 0.5, 1, and 1.5 at. pct) alloys. It is shown that with the increase of Zr, the sequence of phase formation is β-Ti + α-Ti + (Ti, Zr)₃Cu₄ ⇒ β-Ti + α-Ti + TiCu ⇒ β-Ti + Ti₂Cu + glass ⇒ glass ⇒ β-Ti + Ti₂Cu + TiCuSn. The quinary Ti-Zr-Cu-Co-Sn alloy with 12.5 pct Zr exhibits the best GFA. The addition of 1 pct Si results in the improvement of the critical size of glassy rods up to 3 mm in diameter. The yield stress and Young’s modulus of Z-series alloys increases, and the plastic strain decreases with the addition of Zr. The yield stress and ultimate compression stress of Ti₄₆Zr_11.5Cu_31.5Co₇Sn₃Si₁ glassy alloy reach 2477.9 and 2623.3 MPa, respectively. It was found that the addition of Si promotes the generation and multiplication of shear bands, resulting in certain plasticity in these kinds of glassy alloys.