Partial Melting and Resolidification of Single-Component Metal Powder With a Moving Laser Beam

Abstract

Partial melting and resolidification of single-component metal powders with a moving laser beam is investigated numerically. Since laser processing of metal powder is a very rapid process, the liquid layer and solid core of a partially molten powder particle may not at thermal equilibrium and have different temperatures: the temperature of the liquid part is higher than the melting point, and the temperature of the solid core is below the melting point. Therefore, the local temperature of regions with partial molten particles is within a range of temperature adjacent to the melting point, instead of at the melting point. The partial melting of the metal powder is also accompanied by shrinkage that drives out the gas in the powder bed and the powder structure is supported by the solid core of the partially melted powder particles. Melting with shrinkage and resolidification are described using a temperature transforming model. The convection driven by capillary and gravity forces in the melting liquid pool is formulated by using Darcy’s law. The effects of laser beam intensity and scanning velocity on the shape and size of the heat affected zone and molten pool are investigated.