Optimum Zr–Al–Co bulk metallic glass composition Zr53Al23.5Co23.5

Composition criteria based on conduction electron concentration (e/a) have been applied for the bulk metallic glass (BMG) formation in the Zr–Al–Co system. In the phase diagram, three e/a-constant phases AlCo, ZrAlCo and pure Zr constitute a straight line with constant e/a=1.5. Three e/a-variant lines were constructed by linking three specific compositions, Zr78.5Co21.5, Zr70.5Al29.5 and Zr9Co4, to the third elements. The former two compositions correspond to deep eutectics of the binary subsystems while the latter to the basic icosahedral cluster composition of the Ti2Ni-type Zr2Co phase. Easy BMG formation was found in the e/a-constant and the (Zr9Co4)–Al e/a-variant alloy series, while the alloys in the two deep eutectic related composition lines have weaker glass forming abilities (GFAs). BMGs with diameter of 3 mm are obtained along the (Zr9Co4)–Al composition line within an e/a span of 1.3–1.5, and their thermal stabilities and GFAs increase with the e/a ratios. This e/a-variant line intersects the e/a-constant line at the composition Zr53Al23.5Co23.5, which has the highest thermal stability and GFA, characterized by thermodynamic parameters Tg=783 K, Tx=849 K, Tg/Tl=0.590 and γ=0.404.