• Effect of element wall thickness on the homogeneity and isotropy of hardness in SLM IN718 using nanoindentation

      Abo Znemah, Reem; Wood, Paul; Gunputh, Urvashi Fowdar; Zhang, Cheng; Louisiana State University, Baton Rouge, LA; University of Derby; Medtronic Inc., Tempe, Arizona, US (Elsevier, 2020-07-28)
      In this paper the homogeneity and isotropy of the mechanical hardness of thin-walled Inconel 718 (IN718) alloy samples manufactured by Selective Laser Melting (SLM) were examined using nanoindentation testing. SLM-produced honeycombed samples with wall thicknesses of 0.8, 0.6 and 0.4 mm respectively were studied by measuring the hardness across the wall thickness, and on the planes parallel and perpendicular to the build direction over the range of depths of 10-2000 nm. The average hardness values close to the edges were 4.0-6.5% lower than the areas away from the them. Interestingly the average hardness dropped by 15.2% with reduction in the cell wall thickness from 0.8 mm to 0.4 mm. Average hardness values were reported to be higher on the plane perpendicular to the build direction compared to the parallel plane. A variable material length scale was proposed in this work to describe the size effects of the microstructure. It was evaluated using the nanoindentation hardness test results and a computational model developed in previous studies by the first author and his co-workers.