Formation and thermal stability of Ni-based bulk metallic glasses in Ni-Zr-Nb-Al system

An Al element was selected as an alloying metal to improve the glass-forming ability (GFA) of Ni-Zr-Nb alloys. The thermal stability and glass-forming ability of Ni-Zr-Nb-Al alloys were investigated. It was found that the partial substitution of Nb by Al led to significant shift of the onset crystallization temperature Tx and the liquidus temperature Tl, while the glass transition temperature Tg was less composition sensitive. The supercooled liquid region, ΔTx (=Tx-Tg), the reduced glass transition temperature (Tg/Tl) and γ=Tx/(Tg+Tl) increased with increasing Al content up to 5 at%. The best GFA was found at Ni60Zr20Nb15Al5 with a critical diameter of 3 mm. The characteristic parameters are: ΔTx=54 K, Tg/Tl=0.615 and γ=0.405. The maximum values of ΔTx and Tg/Tl were 72K and 0.617, respectively, at Ni60Zr25Nb10Al5. The compression tests showed that the Ni60Zr20Nb15Al5 BMG possessed high fracture strength of 2900 MPa, Young's module of 152 GPa, and plastic elongation of 2.5% at room temperature. (author)