An Investigation into Metallic Powder Thermal Conductivity in Laser Powder Bed Fusion Additive Manufacturing

This study investigates the thermal conductivity of metallic powder in laser powder-bed fusion (LPBF) additive manufacturing. The intent is to utilize a methodology combining laser flash testing, finite element (FE) heat transfer modeling, and an inverse method to indirectly measure the thermal conductivity of nickel-based super alloy 625 (IN625) and titanium alloy (Ti64) powder used in LPBF processes. A hollow test specimen geometry was designed and built with LPBF enclosing the un-melted powder to mimic the powder bed conditions. The specimens were then flash heated in a laser flash system to measure their transient temperature response. Next, a developed FE model and a multi-point optimization algorithm were applied to inversely analyze the thermal transient, and extract the thermal diffusivity and conductivity of the powder enclosed in the specimens. The results indicate that the thermal conductivity of IN625 powder used in LPBF ranges from 0.65 W/(m·K) to 1.02 W/(m·K) at 100 °C and 500 °C, respectively. On the other hand, Ti64 powder has a lower thermal conductivity than IN625 powder, about 35 % to 40 % smaller. However, the thermal conductivity ratio of the powder to the respective solid counterpart is not much different between the two materials, about 4 % to 7 %, which is largely temperature independent.