Strategy for Tailoring Thermoplastic Forming Process in Bulk Metallic Glasses

The technical interest in bulk metallic glasses (BMGs) has grown over the past few decades due to their potential for new applications based on thermoplastic forming (TPF), previously unattainable with conventional crystalline alloys. However, the difficulty in controlling the TPF process due to the metastability of the amorphous phase has posed a barrier to widespread commercial use. This study provides practical guidelines for tailoring the TPF process, incorporating the influence of process variables in BMGs.<br/>Firstly, a practical indicator of the ideal thermoplastic forming ability (TPFA) of metallic glasses (ΔT_F = T_l - T_x) is proposed by comprehensively considering flow instability and phase stability. Using this indicator, it is possible to select superior glass-forming alloy systems with excellent TPFA easily.<br/>Secondly, we accurately identify the TPF window and TPFA according to the heating rate, in a wide range from 10^-1 to 10⁴ K/s, by constructing the continuous heating transform (CHT) diagram with iso-viscosity contours. These approaches enable the selection of customized TPF processes for each amorphous alloy, providing guidelines for tailored TPF processes.<br/>Finally, as an example of a TPF process, we demonstrated excellent thermoplastic formability (TPFA) in Be-free Zr-based MGs with T_g below 350 °C and a wide TPF window over 70 K, which is comparable to advanced engineering plastics like Polyimide, expanding the TPF process to MGs. The findings indicate that even marginal MGs have an advantage in manufacturing micro-to-nano scale products at ultra-fast heating rates, akin to advanced engineering plastics. This work inspires further exploration of MGs as practical materials for industrial applications.