Vaporization of alloying elements and explosion behavior during laser powder bed fusion of Cu–10Zn alloy

Abstract

Vaporization of alloying elements is an important phenomenon during laser powder bed fusion (LPBF), especially in the laser interaction with difficult-to-form materials containing the volatile element as main alloying element, which has a significant effect on the chemical composition, microstructure and mechanical properties. However, the mechanisms of the typical phenomenon in vaporization, such as the explosion, and its influence on the forming quality are not fully understood. Here, based on the in situ high-speed high-resolution imaging, we observe the explosion of the molten pool with temporal scale of ~101 μs and spatial scale of ~101–102 μm during LPBF of Cu–10Zn. This micro-explosion can be attributed to the drastic augment of the saturated vapor pressure of Zn component in the molten pool. Theoretical calculations of vaporization amount in the explosion process by Miedema's model and Langmuir's equation, are agreed well with the experimental results of volume increment for vaporization-induced inflation of the droplet spattering. Moreover, we also reveal a new defect formation mechanism, explosion-induced crater, which is detrimental to the forming quality in LPBF. The explosion-induced crater defect can be mitigated by increasing the lifetime of the molten pool, thus improve the continuity and flatness of the melt track. This study is expected to provide the scientific basis for LPBF of difficult-to-form materials to achieve stable forming with fewer defects.