The influence of pulsed laser powder bed fusion process parameters on Inconel 718 material properties

Abstract

In this work, the effect of pulsed laser used during the powder bed fusion (L-PBF) additive manufacturing (AM) process on Inconel 718 (IN718) material properties has been investigated. Argon gas atomised (AGA) IN718 powder is characterised in terms of flow, density, particle size distribution and morphology. Powder shows mostly spherical morphology with Hausner ratio of 1.17 indicating good flow characteristics. Density optimisation trials are carried out by varying laser power and exposure time. Fabricated samples are characterised in terms of porosity by area fraction analysis using light microscopy and volume fraction analysis using X-ray microcomputed tomography (micro-CT). Minimum porosity of 0.16% is achieved for laser power of 200 W and exposure time of 110 μs＀ Microstructural analysis using the Electron Backscatter Diffraction (EBSD) technique shows limited columnar grain structure in the Z direction and more equiaxed type grains in the XY direction (normal to the Z direction). Tensile test results show 754 MPa yield strength, 1070 MPa ultimate tensile strength and ~24% elongation. Finally, hole drilling residual stress measurements show increase from ~0 MPa to over 450 MPa in tensile stress up to a depth of 1 mm from the top surface of the as-build L-PBF IN718 sample. It has been found that laser pulsing produces higher homogeneity in grain structure and better mechanical properties than that by the continuous laser method.