Finite Element Simulation of the Stress Evolution of the Laser Shock Peening Metallic Bond Coat in High Temperature Thermal Cycles

The work aims to investigate the effect of laser shock peening (LSP) on the stress distribution of thermally grown oxide (TGO) surface and TGO/BC interface during high temperature thermal cycles. Based on the real TGO morphology, the experimentally obtained TGO thicknesses for different times during thermal cycles were fitted, the material transformation method was used to simulate the thickening process of TGO during thermal cycles, a finite element model was established, and two forms of failure in the hazardous area of LSP-modified (LSPed) and non-LSP-modified (Non-LSPed) specimens were analyzed from the perspective of stress evolution. Then, the residual stress test of the oxidized metal bond coats was performed by Raman spectroscopy (RFS). The overall compressive stress on the surface of the TGO increased with the number of thermal cycles and the stress distribution of the TGO exhibited corresponding fluctuations with the topography. The maximum compressive stress on the upper surface of the TGO occurred at the peak, the compressive stress decreased and gradually changed to a tensile stress from the peak to the valley. After 10 thermal cycles, the maximum value of S11 compressive stress on the TGO surface of the LSPed specimen was greater than that of the Non-LSPed specimen, and after 50 thermal cycles, the maximum value of TGO compressive stress on the TGO surface of the LSPed specimen was much smaller than that of the Non-LSPed specimen. As the number of thermal cycles increased, the difference between the S11 stress values at the TGO/BC interface of the two types of specimens became smaller. The maximum values of S22 tensile stress on the TGO surface and at the TGO/BC interface were concentrated in the peak region, and the maximum values of S12 shear stress were located in the peak-waist region midway between the peak and the valley of the wave. The S22 stress on the surface of the TGO of the LSPed specimen increased gradually with the number of thermal cycles, but the S22 tensile stress value was less than 250 MPa and the stress value was generally low. The pattern of changes in S22 and S12 stresses at the TGO/BC interface with the number of cycles was basically the same: after 10 thermal cycles, the S22 and S12 stresses in the LSPed specimens were greater than those in the Non-LSPed specimens; and after 50 thermal cycles, there was little difference in the S22 and S12 stresses at the interface between the two types of specimens. The simulation results obtained from the TGO stress finite element simulation model constructed are consistent with the test results. By regulating the growth rate of TGO, LSP can effectively alleviate the drastic change of stress during the TGO growth process, greatly reduce the maximum S11 and S12 stress on the surface of TGO, and then reduce the occurrence of penetrating cracks perpendicular to the surface and shear failure on the surface of TGO and has little effect on the stress state of the surface of TGO (TGO/BC interface). © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.