Additive manufacturing of crack-free large IN738LC parts through tailored substrate designs

Abstract

Additive Manufacturing (AM) is revolutionizing industrial production by enabling the direct fabrication of intricate geometries, far beyond the capabilities of traditional manufacturing methods. However, stress-induced cracking remains a significant challenge in AM, especially in hard-to-weld metallic materials like the Ni-based superalloy IN738LC. To address this issue, a novel substrate design has been developed for Laser Directed Energy Deposition (L-DED) to mitigate stress and prevent crack formation. This innovative substrate allows for more unrestricted thermal expansion and contraction of the deposited layers, a key factor in preventing stress accumulation that typically leads to cracking. To validate its effectiveness, IN738LC components were fabricated using both standard and designed substrates. In-situ temperature and displacement measurements were recorded throughout the L-DED process, and the data were used to calibrate a specialized thermo-mechanical finite element model tailored for AM. The simulations identified areas of high stress concentrations and potential cracking sites. With the standard substrate, cracks were observed to initiate, propagate and self-seal during the L-DED process. In contrast, the designed substrate completely eliminated stress accumulation, preventing any cracking. This novel approach successfully enabled the production of large-scale (over 220 mm) crack-free IN738LC components without the need for preheating, additional equipment, or modifications to the alloy composition—requirements that were previously considered essential. Moreover, the mechanical properties of the fabricated components were significantly improved, achieving a tensile strength of 1152.7 MPa and an elongation of 16.1 %, demonstrating the potential of this substrate design to advance the fabrication of industrial components.