Characterization an‎d Investigation of the Microstructure an‎d Mechanical Properties of Nickel-Based Superalloy IN738 Coated with IN625 Using selec‎tive Laser Melting

11/1/2025 12:00:00 AM

Nickel-based superalloys are widely used in gas turbine components due to their high-temperature properties. However, their high strength, high melting point, an‎d poor machinability make manufacturing an‎d repair costly an‎d challenging. Additive manufacturing (AM), especially for repairing components with complex geometries, offers an effective solution. While most previous studies have focused on Directed Energy Deposition (DED), in this research the non-weldable IN738 substrate was repaired using the Powder Bed Fusion (PBF) process with the weldable IN625 alloy. The PBF method provides much higher precision compared to DED, though it has been rarely investigated for such applications. This study concentrated on depositing the first four layers of IN625 (30 µm thickness each) on IN738, since this region is most susceptible to defects an‎d cracks. To reduce crack sensitivity caused by precipitate phases, the substrate was heat-treated prior to the process, which reduced the γ′ phase fraction from 35% to 3.3% an‎d carbides from 2.7% to 0.8%. The influence of process parameters, including laser power (100, 150, an‎d 200 W) an‎d scan speed (100–2700 mm/s), was then eva‎luated. Results showed that increasing power promoted elemental homogenization an‎d reduced cracking, whereas increasing scan speed led to elemental segregation behind the melt pool interface, thereby promoting crack formation. A direct relationship between microhardness an‎d cracking was identified, with a critical microhardness threshold of HV0.2 256 required for crack-free deposition. Based on these findings, an optimal processing window was determined: 200 W at 140 mm/s an‎d 163 W at 100 mm/s. Microstructural analysis revealed that changes in solidified sub-grain size an‎d an increased width-to-depth ratio (w/d) of the melt pool played an important role in preventing pore formation. Finally, tensile tests at room an‎d elevated temperatures confirmed the integrity of the repair: the joint achieved up to 95% of IN625 strength an‎d 89% of IN738 strength, while maintaining 79–83% of the substrate’s tensile strength under turbine operating conditions. These results demonstrate that successful repair of the non-weldable IN738 substrate by LPBF is possible without preheating.

ساخت افزايشي بستر پودر , ترك , حفره , IN738 , IN625

Laser Powder Bed Fusion (LPBF) , Crack , pore , IN738 , IN625

Amirhossein Riazi

Dr. Seyed Hossein Razavi, Dr. Alireza Khavandi