Microstructure refinement and work hardening in a machined surface layer induced by turning Inconel 718 super alloy
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The microstructural changes in the machined surface layer of Ni-based super alloys essentially determine the final performance of the structural components of aerospace engines in which these alloys are used. In this work, multiscale metallurgical observations using scanning electron microscopy, electron-backscatter diffraction microscopy, and transmission electron microscopy were conducted to quantitatively characterize the microstructure of the machined subsurface. Next, to elucidate the factors that affect the formation of the refinement microstructure, the distributions of the deformation parameters (strain, strain rate, and temperature) in the machined subsurface were analyzed. A dislocation-twin interaction dynamic recrystallization mechanism for grain refinement during machining of Inconel 718 is proposed. Furthermore, microhardness evolution induced by grain refinement in the machined surface is evaluated. The results suggest that the gradient microstructure and the work hardening can be optimized by controlling the cutting parameters during turning of Inconel 718.
Keywordsgrain refinement dislocation-twin interaction work hardening turning Inconel 718
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The authors would like to acknowledge the financial support from the National Natural Science Foundation of China (No. 51425503) and the Major Science and Technology Program of High-end CNC Machine Tools and Basic Manufacturing Equipment of China (No. 2014ZX04012014). This work was also supported by a grant from the Taishan Scholar Foundation of Shandong province (No. TS20130922).
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