The Crystallization Mechanism of Zr-Based Bulk Metallic Glass during Electron Beam Remelting

Abstract

Bulk metallic glasses (BMGs) are promising for multifunctional and structural application in different industries. However, the limited size of BMGs hinders their further application. The welding of BMGs has shown the possibility of getting rid of the casting size limitation. The heat-affected zone (HAZ) and fusion zone (FZ) often undergo severe crystallization during the welding process. It is still unclear whether the crystallization occurs during the heating process or the cooling process. To figure out the crystallization mechanisms of Zr-based BMGs during the electron beam welding process, the Zr-based BMGs with the composition of Zr41.2Ti13.8Cu12.5Ni10Be22.5 were remelted by electron beam. The microstructures of the HAZ and the remelting zone (RZ) were analyzed. The thermal field of the electron beam welding was obtained by the finite element method (FEM). The critical conditions for crystallization during the heating and cooling processes were obtained by differential scanning calorimetry (DSC) and the Kissinger equation. The results show that the Zr41.2Ti13.8Cu12.5Ni10Be22.5 in the HAZ undergoes severe crystallization, while the Zr41.2Ti13.8Cu12.5Ni10Be22.5 in RZ keeps amorphous state after the remelting process. The low cooling rate in the HAZ is responsible for its crystallization.

Keywords

• electron beam remelting
• BMGs
• microstructures
• critical cooling or heating rate
• FEM