Abstract
A method to find the optimum process parameters for manufacturing nickel-based superalloy Inconel 738LC by laser powder bed fusion (LPBF) technology is presented. This material is known to form cracks during its processing by LPBF technology; thus, process parameters have to be optimized to get a high quality product. In this work, the objective of the optimization was to obtain samples with fewer pores and cracks. A design of experiments (DoE) technique was implemented to define the reduced set of samples. Each sample was manufactured by LPBF with a specific combination of laser power, laser scan speed, hatch distance and scan strategy parameters. Using the porosity and crack density results obtained from the DoE samples, quadratic models were fitted, which allowed identifying the optimal working point by applying the response surface method (RSM). Finally, five samples with the predicted optimal processing parameters were fabricated. The examination of these samples showed that it was possible to manufacture IN738LC samples free of cracks and with a porosity percentage below 0.1%. Therefore, it was demonstrated that RSM is suitable for obtaining optimum process parameters for IN738LC alloy manufacturing by LPBF technology.
Highlights
Laser powder bed fusion (LPBF) is an additive manufacturing technology in which a laser melts successive powder layers in order to build the final part [1]
Using the porosity and crack density results obtained from the design of experiments (DoE) samples, quadratic models were fitted, which allowed identifying the optimal working point by applying the response surface method (RSM)
It was demonstrated that RSM is suitable for obtaining optimum process parameters for Inconel 738LC (IN738LC) alloy manufacturing by laser powder bed fusion (LPBF) technology
Summary
Laser powder bed fusion (LPBF) is an additive manufacturing technology in which a laser melts successive powder layers in order to build the final part [1]. Some of the LPBF process parameters are laser power (P), hatch distance (h), laser scan speed (v), layer thickness (t), baseplate preheating temperature and laser scan strategy (θ). The latter refers to the rotation of successive layers during the manufacturing process. Compared with conventional manufacturing processes (cast and wrought), LPBF technology offers some advantages, such as design freedom, reduced weight of parts, processing of complex parts, manufacturing of near-net-shape components and reduction of waste material [3] Despite these advantages, the presence of defects such as pores and cracks in the manufactured final parts is a drawback for the implementation of this technology in the industry [4]. The existence of porosity is attributed to different mechanisms: insufficient energy density, porosity in raw material, Materials 2020, 13, 4879; doi:10.3390/ma13214879 www.mdpi.com/journal/materials
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