Controlling heat accumulation through changing time per layer in laser powder bed fusion of nickel-based superalloy

Feedforward/feedback control of laser powder bed fusion (L-PBF) was proposed over a decade ago but remains challenging. Despite numerous parameters involved, most studies have attempted to control the process by changing laser power only. On the other hand, previous studies have shown that reducing the time per layer ($\mathrm{TPL}$) increases the heat accumulation during the process. Thus, this feasibility study aimed to validate $\mathrm{TPL}$ as a potential parameter to control the top surface temperature of a nickel-based superalloy sample during L-PBF. First, a part-scale finite element thermal analysis with feedback control was performed to verify the temperature control strategy. Then, the sample was experimentally fabricated with the temperature control by changing $\mathrm{TPL}$. The measured temperature was successfully maintained at target values (400, 500, and 700 °C), which were switched every 100 layers. In the as-fabricated IN738LC sample with the temperature control, the cellular microstructures coarsened by more than 0.5 μm and the hardness increased by approximately 50 HV as the target temperature was set higher. While demonstrating the potential of $\mathrm{TPL}$ for temperature control, its limitations in practical manufacturing were also discussed.