Effect of real-time cooling rate on microstructure in Laser Additive Manufacturing

An infrared thermal imaging system is developed to compare the effects of cooling rate and melt pool temperature on the microstructure of 316L stainless steel produced by Laser Additive Manufacturing (LAM) with injected powder melting. The system captures the real-time cooling rate to provide online monitoring and control of the microstructure at the onset of solidification. Further study is conducted to evaluate cooling rate effects on grain size, phase transformations and hardness. Cooling rate changes are also studied with respect to the traveling speed, in order to identify a suitable controlling action for a microstructural controller. The study provides a strong experimental justification of the current theories in solidification and microstructural evolution during the LAM with injected powder melting process.