On the adhesion between metallic glass and dies during thermoplastic forming

Thermoplastic forming (TPF) is an efficient process for the fabrication of metallic glass (MG) components. However, the MG-die adhesion has been one of the crucial issues in the TPF production. This paper presents comprehensive experimental and theoretical studies on the adhesion between two typical MGs (La-based and Zr-based) and various die materials including electroless Ni-P, Si, polytetrafluoroethylene (PTFE), sapphire and SiC. It was found that of the above die materials investigated, PTFE and sapphire were the best in preventing adhesion followed by SiC, electroless Ni-P and Si. Further theoretical prediction also indicated that the work of adhesion of PTFE and sapphire are the lowest among the employed dies, which agrees very well with the experimental results. However, the low melting point of PTFE makes it not a suitable die material for the TPF of some MGs. By considering a number of forming requirements and conditions, this study concluded that sapphire is the best die material for the thermoplastic forming of MG components.