| YU Yan-qing,ZHOU Liu-cheng,GONG Jian-en,FANG Xiu-yang,ZHOU Jie,CAI Zhen-bing.Microstructure and Fretting Fatigue Behaviour of GH4169 Superalloy after Laser Shock Peening[J],51(10):38-48 |
| Microstructure and Fretting Fatigue Behaviour of GH4169 Superalloy after Laser Shock Peening |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.10.005 |
| KeyWord:GH4169 superalloy laser shock peening microstructure fretting fatigue fracture morphology crack propagation |
| Author | Institution |
| YU Yan-qing |
School of Mechanical Engineering, Southwest Jiaotong University, Chengdu , China |
| ZHOU Liu-cheng |
Science and Technology on Plasma Dynamic Laboratory, Aeronautics Engineering College, Air Force Engineering University, Xi’an , China |
| GONG Jian-en |
School of Mechanical Engineering, Southwest Jiaotong University, Chengdu , China |
| FANG Xiu-yang |
School of Mechanical Engineering, Southwest Jiaotong University, Chengdu , China |
| ZHOU Jie |
School of Mechanical Engineering, Southwest Jiaotong University, Chengdu , China |
| CAI Zhen-bing |
School of Mechanical Engineering, Southwest Jiaotong University, Chengdu , China |
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| Abstract: |
| To improve the fretting fatigue lifetime of GH4169 Ni-based superalloy, in this paper, laser shock peening (LSP) was performed on the surface of GH4169 dovetail structure. The laser energy of 5 J, the pulse duration of 20 ns, the spot diameter of 2.2 mm, the overlap rate of 50%, the repetition of 1 Hz, and the scan number of 1 cycle were adopted in this study. The laser scanning confocal microscope (LSCM) was used to obtain the 3D surface morphology and 2D profile after LSP. The X-ray diffractometer (XRD) was evaluated to analyze the phase composition change before and after LSP. The micro-hardness and residual stress were measured by the vickers hardness tester and X-ray stress analyzer, respectively. The fretting fatigue performance of GH4169 superalloy was performed on the high-frequency fatigue testing machine with a maximum load of 20 kN and stress ratio of 0.1. The fretting fatigue lifetime and crack propagation were collected to analyze the difference before and after LSP. The optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the fracture morphology. The results indicate that the surface hardness of LSPed sample is increased by 17.3% compared to the untreated sample. The hardened layer is about 0.63 mm. The surface compressive residual stress is 331.5 MPa. The surface roughness (Sa) is increased from 1.62 μm to 13.89 μm after LSP. The grain size of LSPed sample in the deformed layer has no obvious refinement, which indicates the formation of dislocation rather than the motion of dislocation in the surface layer of GH4169 superalloy under the action of the laser shock wave. Similar to the untreated sample, the fracture mechanism changes from the quasi-cleavage fracture to the ductile fracture with a fatigue stripe along with the crack propagation. However, after LSP, the number of crack sources decreases from multiple fatigue sources to single fatigue sources. Besides, the crack initial site is also changed from the surface to the sub-surface, which is 234 μm from the surface. The overall fatigue lifetime of LSPed sample is increased by 827% compared to the untreated sample under the maximum load of 22 kN, which is primarily provided by the enhancement of crack initiation lifetime. The formed hardened layer can improve the surface wear resistance and reduce the micro-crack initiation probability. The formed compressive residual stress field can reduce the average stress. Therefore, LSP can significantly increase the initial resistance of GH4169 superalloy. However, the propagation lifetime of the untreated sample accounts for about 54.4% of the overall lifetime, while that of LSPed sample accounts for about 0.3% of the overall lifetime. The spacing of fatigue stripe is also increased from 0.50 μm to 1.01 μm after LSP. The spacing of fatigue stripe represents the distance of a single cycle, indicating that a shorter spacing leads to a faster propagation rate. The faster propagation rate after LSP may be ascribed to the sudden change and relaxation of residual stress below the compressive residual stress field. The fretting fatigue performance of GH4169 superalloy dovetail structure is significantly improved under the combined action of hardened layer and compressive residual stress field induced by LSP. |
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