Laser Shot Peening of Inconel 600 and Surface Morphology Characterization
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Laser Shot Peening of Inconel 600 and Surface Morphology Characterization 1
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A. A. Bugayev, M. C. Gupta, J. Orr , S. Levesque , and R. Payne Applied Research Center, Old Dominion University, 12050 Jefferson Avenue, Newport News, Virginia 23606, U.S.A. 1 Framatome ANP, Inc, Lynchburg, Virginia 24506, U.S.A. ABSTRACT
The results on laser shot peening and its characterization for Inconel 600 are presented. Using an X-ray diffraction technique we show that the residual compressive stresses can be successfully induced in Inconel 600 with parameters of laser peening, which are close to that of 316L stainless steel. The on-line monitoring system involving the acoustic pulse measurements is described for quality control of laser shot peening process. We found that sample scanning during laser processing results in a system of column-like microstructure, which is tilted in direction of scanning. The features of optical properties of tilted microstructure are described. We revealed that the base material injected into the confining water due to laser ablation is transformed to spherical nanoparticles with diameter of 60 nm. INTRODUCTION Laser shot processing (peening) (LSP) is a surface treatment technology, which consists of irradiating a metallic target with a short and intense laser pulse in order to generate, through high-pressure surface plasma, a plastic deformation and a surface strengthening. Particular benefit is achieved for improving the fatigue behavior [1], and the stress corrosion cracking of various materials like austenitic stainless steel in power plants [2,3]. By now the theoretical aspects of LSP are well elaborated and are widely presented in many publications, which describe physical processes of laser-driven shock wave generation [4,5], models of pressure generation [6-8], and mechanics of a laser shock interaction with matter [9]. Meanwhile the experimental conditions of LSP allow one to create considerable changes of the surface morphology of the treated metal in a form of surface structures. Actually a large variety of the surface relief structures were observed with the laser energy higher than the melting threshold for semiconductors and metals. According to their shape these structures could be roughly divided into three groups. The first group of structures (ripples) is due to the development of the capillary wave instability due to nonuniform interference field. The presence of a strong correlation between the parameters of the structures and the characteristics of the laser irradiation allow one to speak about “laser-induced capillary waves” [10]. The second group (cellular structures) arises is resulted from instability of capillary waves due to thermal-capillary effects in laser-melted film [11]. The structures mentioned above were obtained at single-shot irradiation conditions. The third group is represented by conical and column microstructures, which are developed 4 during multi-shot irradiation (up to 10 laser shots) [12,13]. In this paper the results are presented on the L
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