Yunxia Ye

Cyclic oxidation resistance of In718 superalloy treated by laser peening

The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening(LP). Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ° for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope (SEM), energy-dispersive spectra (EDS), transmission electron microscope (TEM) and X-ray diffraction technique (XRD), respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing (Fe,Cr)2O3, NiCrO3 and Ni(Al,Cr)2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.

High temperature wear performance of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy subjected to laser shock peening

ABSTRACT This paper investigates the influence of laser shock peening (LSP) parameters on surface integrities and high temperature wear performances of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy. Surface integrities include surface roughness, residual stress and micro-hardness are measured. High temperature wear performance of TC11 alloy with and without LSP are investigated. The results indicate that multiple LSP impacts can improve surface micro-hardness and induce compressive residual stress in the surface layer. Moreover, the friction coefficient and wear rate of TC11 alloy significantly decrease after LSP with optimised parameters. The improved wear performance is ascribed to the low surface roughness, higher surface micro-hardness and compressive residual stress induced by multiple LSP impacts in the surface layer.

Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing

Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing (LSP) was investigated. The residual stress of the specimens treated with LSP was assessed by X-ray diffraction method. The microstructure and fracture morphology were characterized by using an optical microscope (OM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The results indicated that the maximum residual compressive stress was at about 1 mm from the shocking spot center, where the residual compressive stress was slightly lower. High density tangling dislocations, dislocation walls, and dislocation cells in the microstructure of the specimens treated with LSP effectively prevented fatigue cracks propagation. The fatigue life was roughly twice as long as that of the specimens without LSP. The fatigue crack initiation (FCI) in specimens treated with LSP was observed in the lateral section and the subsurface simultaneously. The fatigue striation in the fracture treated with LSP was narrower than that in the untreated specimens. Moreover, dimples with tear ridges were found in the fatigued zones of the LSP treated specimens, which would be caused by severe plastic deformation.

Laser shock microforming of aluminum foil with fs laser

Laser shock microforming of Aluminum(Al) foil through fs laser has been researched in this paper. The influences of confining layer, clamping method and impact times on induced dent depths were investigated experimentally. Microstructure of fs laser shock forming Al foil was observed through Transmission electron microscopy (TEM). Under the condition of tightly clamping, the dent depths increase with impact times and finally tend to saturating. Another new confining layer, the main component of which is polypropylene, was applied and the confining effect of it is better because of its higher impedance. TEM results show that dislocation is one of the main deformation mechanisms of fs laser shock forming Al foil. Specially, most of dislocations exist in the form of short and discrete dislocation lines. Parallel straight dislocation slip line also were observed. We analyzed that these unique dislocation arrangements are due to fs laser-induced ultra high strain rate.

Study of the substructure in nanometer copper thin films treated by laser shock processing

We study nanometer copper thin films prepared by magnetron sputtering and treated with laser shock processing (LSP). We observe the formation of firstborn twin crystals and some complete twin crystals in the copper thin films. After LSP, scanning electron microscope (SEM) images show obvious plastic deformation of the copper grain on the film surface, dramatically increased grain size, and the appearance of a large number of twin crystals. Moreover, the width of the crystals is a few dozen nanometers, and the cross angle is more than or close to 90o. Many vacancy defects appear during the sliding of atomic plane, which leads to a faulty structure; however, no obvious dislocation is observed. These substructures play a significant role in improving the mechanical performance of nanometer copper thin films.