Absorption coefficient characterization in Ti-6Al-4V laser additive manufacturing

Abstract

In order to accurately model the laser deposition of Ti-6Al-4V aerospace components, the interaction of the laser and metal powder feedstock has been investigated. One of the key modeling parameters, the absorption coefficient of the material, is often unknown for material in powder form. It has been shown that the absorption coefficient of powdered material is higher than solid material due to trapping and re-reflection of the laser energy within the powder bed. The current work focuses on determining the absorption coefficient of liquid Ti-6Al-4V irradiated usinga 1.1 and 4.4kW CO2 laser. Ti-6Al-4V samples containing a known mass of spherical Ti-6Al-4V powder were irradiated using a high energy CO2 laser. Knowing the equilibrium temperature as well as the transient response from thermocouple data at three locations, the laser’s absorbed energy can be found. Each sample, though similar, receives a different irradiation time. Combining the results of multiple samples, values of absorption coefficients are determined versus irradiation time. The absorption coefficients of the powder feedstock are on average, significantly greater than the absorption coefficient of a solid (machined) surface.