Evolution of crystalline phase during laser processing of Zr-based metallic glass

Understanding the crystallization behavior of metallic glasses (MGs) during laser processing is important in additive manufacturing of MGs, which would overcome the limitation of section-thickness. Experiments were conducted to study the crystalline phase evolution, particularly in the heat-affected zone (HAZ), during laser processing of LM105 (Zr52.5Ti5Al10Ni14.6Cu17.9 (at.%)) MG plates. Three regions with distinct degree of crystallization in HAZ were found, which were caused by different thermal histories. The crystallization can be suppressed, however, by increasing the laser scan speed (100 mm/s in this study) while the laser power is fixed (100 W in this study). A complete model integrating the heat transfer and the classical nucleation/growth theory was developed to calculate the thermal history and the evolution of crystalline volume fraction. Modeling predictions on the depth of fusion zone (FZ) and thickness of HAZ for different laser processing parameters were validated by comparing with the experimental measurements. This study has demonstrated that at a specific location in the MG material, the use of critical cooling rate alone is not adequate to determine if the material is crystallized; instead the thermal history that the material experienced during both the laser heating and cooling processes is the key factor affecting the final crystallization. The model provides comprehensive understanding of the crystallization behavior during laser-MG interaction.