Effects of increasing powder layer thickness on the microstructure, mechanical properties, and failure mechanism of IN718 superalloy fabricated by laser powder bed fusion

• Published in: International journal of advanced manufacturing technology 2022, Vol.118 (5-6), p.1703-1717
• Main Authors: Badrossamay, Mohsen, Rezaei, Ali, Foroozmehr, Ehsan, Maleki, Ali, Foroozmehr, Ali
• Format: Article
• Language: English
• Subjects: CAE) and Design; Coalescing; Computer-Aided Engineering (CAD; Crack initiation; Creep life; Diameters; Electron backscatter diffraction; Emission analysis; Engineering; Failure mechanisms; Field emission microscopy; High temperature; Industrial and Production Engineering; Mechanical Engineering; Mechanical properties; Media Management; Microstructure; Nickel base alloys; Optical microscopes; Original Article; Powder beds; Rapid prototyping; Room temperature; Rupture tests; Superalloys; Tensile properties; Tensile tests; Thickness
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-021-07719-7

Increasing powder layer thickness could undoubtedly raise the productivity of the laser powder bed fusion (LPBF) process. On the other hand, it may cause some microstructural side-effects, which in turn influence the mechanical properties of the final part. In this work, the effects of increasing powder layer thickness from 30 to 50 μm were studied on the microstructure, tensile, and creep life of LPBF Inconel 718 (IN718). Microstructural investigations were done by optical microscope, field emission scanning electron microscope, and electron backscatter diffraction. Tensile tests were conducted at room temperature as well as 650 ֯C, and stress-rupture tests were performed in standard incremental mode. The results showed that by using 66% thicker powder layers, the intercellular spacing increased from 480 to 1000 nm and diameter of columnar grains enlarged from 38.6 to 69.3 μm. Also, coarser intercellular particles precipitated in continuous form. These microstructural changes led to slight variations in tensile properties at both room and high temperatures. On the other side, significant changes were observed in the creep life of the samples produced with different layer thicknesses. It was discovered that although the specimens produced with 30 μm layer thickness had 0.82% lower relative density, they exhibited 1.7 times longer creep life compared to those fabricated by 50 μm powder layer thickness. Furthermore, fractography showed the lack-of-fusions(LOFs) were the main crack initiators during the tensile tests, while intergranular cracking due to coalescence of spherical cavities caused the high-temperature failure during creep.