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The effects of laser shock processing (LSP) on the microstructures and high-temperature-oxidation resistance of the specimens with the aluminized coatings were investigated. Electron backscattered diffraction, transmission electron microscopy, and scanning electron microscopy were used to characterize the microstructures of the specimens before and after LSP. The results show that the aluminized coating is mainly composed of nanoscale NiAl, Ni 2 Al 3 , and a small concentration of Al 86 Cr 14. The shock waves induced by LSP produced only a few crystal defects in the coating, while a large number of dislocation lines, dislocation tangles and dislocation arrays generated by LSP refine the coarse grains of the substrate. The regulating effects of the LSP on the coating surface help form a continuous and dense oxidation film very quickly, delaying the phase transition (θ-Al 2 O 3 to α-Al 2 O 3). Thus, the high-temperature-oxidation resistance is significantly improved by LSP. • Nanoscale grains of the aluminized coating by pack cementation are shown. • Effects of LSP on microstructures of the coating and substrate are studied. • High temperature oxidation resistance of coatings is improved significantly by LSP. • LSP helps delay the phase transition (θ-Al 2 O 3 to α-Al 2 O 3). [ABSTRACT FROM AUTHOR]

Laser shock processing (LSP) is employed to improve the high temperature oxidation resistance of Ni-based superalloy GH202. Many crystal defects of the surface after treated were found by transmission electron microscope. The residual compressive stress (maximum −305 MPa) and the micro-hardness (maximum 579 HV) of specimens treated were improved significantly. The isothermal oxidation kinetics of GH202 before and after LSP showed that the weight gain of all the treated specimens slowed relatively, and it was more obviously at 900 °C. The oxidation film of the LSP-treated GH202 was mainly composed of Cr 2 O 3 , TiO 2 , NiCr 2 O 4 and a little of Al 2 O 3 . High density dislocations provided many channels of Cr 3+ diffusing to the surface of the LSP-treated GH202, which would facilitate formation of a denser protective oxidation film compared to untreated specimens. The results showed that the high temperature oxidation resistance of the LSP-treated GH202 was improved, especially more significantly at 900 °C. [ABSTRACT FROM AUTHOR]

The effects of laser shock processing on microstructure, the residual stress, and hot corrosion behavior of the Ni-based superalloy GH202 were investigated. The microstructures of GH202 before and after laser shock processing (LSP) were characterized by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). A large number of crystal defects (twins, dislocation arrays, and high dense tangles) were generated on the surface of GH202 treated with LSP. The cross-sectional compressive residual stress and micro-hardness of specimens treated by LSP were improved significantly. The corrosion kinetics of GH202 with or without LSP treatment at 800 °C and 900 °C were investigated. Analysis by X-ray diffraction (XRD) revealed that the corrosion products mainly consist of Cr 2 O 3 , TiO 2 , Al 2 O 3 , NiO, CrS, Ni 3 S 2 , and Na 2 CrO 4 . The surface and cross-section morphologies were observed by scanning electron microscope (SEM) combined with energy dispersive spectroscopy (EDS). The results confirmed that the crystal defects induced by LSP promotes the creation of diffusion paths for elements (Cr, Al, and Ti), allowing the formation of tiny homogeneous oxidation films in a very short time. Additionally, the spallation of oxidation film on the treated specimens was alleviated significantly. Overall, the hot corrosion resistance of Ni-based GH202 induced by LSP was improved in Na 2 SO 4 and NaCl molten salt from 800 °C to 900 °C. [ABSTRACT FROM AUTHOR]

• Microstructural evolution of cross-sections was revealed after LSP. • Low-angle grain boundaries, twins and motion of dislocations were characterized. • Slip and twinning of crystals in cross-sections were observed during LSP. • The multisystem slippage induced by LSP promoted the refinement of grains. Microstructural evolution in the cross-section of Ni-based superalloy GH202 treated by high power laser shock processing (LSP) were investigated. The microstructures on surfaces and cross-sections of alloy specimens were characterized by electron backscatter diffraction and transmission electron microscopy. The results showed that dislocation slip and twinning were generated simultaneously during plastic deformation induced by high power LSP, with many low-angle grain boundaries and twins produced in the surface. The dynamic recrystallization occurred at the spot overlap after LSP due to the crystal migration and subgrain rotation. The dislocation multiplication promoted dislocations to pile up and form dislocation stacking and tangling in the subsurface. The multisystem slippage occurred in the plastic deformation induced by LSP from 40 to 130 μm depth and the motion of dislocation lines in two or more slip systems formed dislocation arrays and subgrains. In areas over 200 μm depth from the surface, dislocation density significantly decreased and a small amount of subgrains and dislocation cells remained. Therefore, LSP had a positive effect on grain refinement, formation of low-angle grain boundaries, and mechanical property improvements. [ABSTRACT FROM AUTHOR]