Volatile alloying elements modulate laser-induced arc stability: A material-dependent interaction mechanism

It is generally known that a laser can stabilize an arc. However, some numerical studies suggested that the laser-induced metal vapor decreased the temperature and electrical conductivity of arc plasma in hybrid laser-arc processing.In this study, the effects of volatile alloying elements on the interaction between laser and arc in hybrid laser-gas metal arc welding (GMAW)-based directed energy deposition (DED) were investigated based on experimental observations and theoretical calculations. The generation of metal vapor reduces the molten pool temperature through the thermal effect, while enhancing plasma conductivity through the electrical effect. The combined action of both determines the stability of the arc. Although the boiling point and first ionization energy of Al were significantly lower than those of Ti, its much lower content reduced its activity and vapor pressure, leading to weaker evaporation in hybrid laser-GMAW-based DED of Ti6Al4V alloy. Owing to its lower boiling point and ionization energy, slightly lower content, the evaporation and ionization of Cr were dominant in hybrid laser-GMAW-based DED of 316L stainless steel. The laser-induced Ti and Cr vapors could provide stable conductive channels for the arc in hybrid laser-arc processing.