Co–B–Si–Ta bulk metallic glasses designed using cluster line and alloying

The formations of Co-based Co–B–Si–Ta bulk metallic glasses, as well as their mechanical and corrosion properties have been explored in this work. The alloy compositions were designed by using the cluster line approach and the alloying strategy, where the cluster line referred to a straight composition line linking a specific binary cluster to the third element in a ternary alloy phase diagram. The base ternary compositions in the Co–B–Si ternary system were first determined by the intersection points of two cluster lines, Co–B cluster to Si and Co–Si cluster to B. Then these basic ternary compositions were a small amount of Ta alloyed to further improve the glass-forming abilities. Experimental results revealed that good glass formers with 4 mm in diameter occurred at Co62.2B26.9Si6.9Ta4, obtained by Ta alloying of the base intersection compositions of Co7B3–Si with Co9Si–B. This bulk metallic glass have not only high thermal stabilities with high Tg and Tx values, but also exhibit high fracture strength of about 4760 MPa, high Vickers hardness of about 1460, a Young's modulus of 198 GPa, and good corrosion resistances in 1 mol/L HCl and 3 mass% NaCl solutions.