PSI - Issue 19

Lloyd Hackel et al. / Procedia Structural Integrity 19 (2019) 452–462 Valentin LOURY--MALHERBE/ Structural Integrity Procedia 00 (2019) 000–000

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compressive stress for this process is represented by the filled triangles in Figure 2 where we see that, except for a thin layer near the surface where the stress has dropped to 280 MPa (40 ksi), fully 75% of the original stress has been retained to the 1 mm depth. Using a diffusion argument for the annealing process, full retention of stress deeper than 1 mm after the 48 hour exposure at 760oC would reasonably be anticipated. As it will be shown, extended variants of LP+TME prove to be beneficial to fatigue lifetimes.

5. Additively Manufactured In718 test samples: The AM Inconel 718 fatigue test samples of a design for testing in 4-point bending analyzed in this work were fabricated by means of direct metal laser sintering (DMLS, MBFZ Toolcraft GmbH, Germany). A layer thickness of 30 μm was employed throughout the fabrication process. As-built specimen dimensions were measured to be 120 mm in length, 11 mm wide, and 21 mm in height. A 2.5 mm radius was incorporated into the component’s geometry to simulate the leading edge of a turbine blade. In the processing specific samples were either shot peened, dual shot peened, laser peened, polished or some combination of these parameters. Selected samples were polished using abrasive paper of successively decreasing grit of 600, 100, and 3000 to ensure a smooth and uniform surface, and to avoid potential stress concentration as a result of significant topographical dissimilarities. The shot peening was performed using 0.3 mm shot size with a “medium” intensity (A scale) process and the dual shot peening was first done with the “medium” process followed by a “high” intensity (C-scale) process. Variants of the LP + TME process were also evaluated. The tests were focused on demonstrating fatigue enhancement of In718 after 350 hours exposure at 600oC regarding jet engine turbine applications.

Figure 3. AM In718 fatigue test samples manufactured for 4-point bend testing. The 4-point bend test configuration provides uniform stress across a wide range of the gauge section.