PSI - Issue 56

Sapam Ningthemba Singh et al. / Procedia Structural Integrity 56 (2024) 11–18 Sapam Ningthemba Singh et al./ Structural Integrity Procedia 00 (2019) 000–000

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LSP PBF SLM SEM

laser shock peening powder bed fusion selective laser melting

scanning electron microscope

2. Methods and materials The fatigue samples were prepared in the Meltio M450 DED machine according to the ASTM E-466/22 standard with the process parameters given in Table 1. Ti6Al4V wire alloy of 1 mm diameter was supplied for an average layer thickness of 1.2 mm during the deposition process. Constant Argon gas was supplied to prevent immediate oxidation during the deposition process. Air conditioning was also maintained in the printing chamber. An initial periphery deposition around the fatigue samples was adopted and then an alternate 45 0 deposition pattern was used in between the layers. The fabricated samples were separated from the substrate by using wire-cut electrical discharge machining (wire-cut EDM). The surfaces were machine and polished with grit sizes ranging from 100 to 2200 to obtain a crack free, flat polished surface before the fatigue test and LSP process. Fig. 1(a) shows as-printed samples, Fig. 1(b) shows the machined surface and Fig. 1(c) shows the polished samples. One set of samples was subjected to the LSP process. The fatigue samples were peened two times on both sides using a Litron Nd:YAG laser of 1064 nm wavelength with a laser diameter of 0.8 mm, and a spot overlapping of 60%. A pulse width of 6 ns and repetition rate of 10 Hz with a maximum energy of 370 mJ was applied. To provide the maximum possible pressure, an overlay of water was provided. A sacrificial layer of black tape was provided to minimize material ablation on the Ti6Al4V alloy. Fig. 2 shows the LSP setup where a focusing lens is used to focus the laser from the deflecting lens on the samples, as shown in Fig. 2(a). The sample is kept inside a tray controlled by CNC. A constant stream of water is supplied, as seen in Fig. 2(b). The LSPed samples are shown in Fig. 2(c). The fatigue test was conducted on both sets of samples: (a) LDED only and (b) LDED+LSPed samples under the load of 650 MPa and a load ratio -1 with 5 Hz frequency for sample numbers 1, 2, and 4. For sample no. 3, different frequency ranges (5 Hz, 10 Hz, and 15 Hz) were used to test the reaction of the samples under different frequencies. The fractured surfaces were analyzed using a scanning electron microscope (SEM) to study the fractography and microstructural details. . Table 1. Process parameters used during the LDED process. Dataset no. 1 2 3 4 Power (W) 800 850 900 950 Speed (mm/s) 10 10 13 13 Layer thickness (mm) 1.2 Wire diameter (mm) 1 Deposition pattern Alternative 45 0 deposition with initial periphery deposition