Machined Surface Integrity For Nickel-Based Superalloy In High-Speed Milling

Nickel-based superalloy plays an important role in the entire field of superalloys. It has been widely used in the manufacture of hot components in aviation jet engines, industrial gas turbines and so on. Nickel-based superalloy GH4169and PM nickel-based superalloy FGH95are the representatives of the nickel-base superalloy. They have the typical advantages of the nickel-base superalloy and have had a wide range of applications in the aerospace components. With aerospace industry development which requests to improve the component quality and productivity, the surface integrity of high-speed machining of FGH95and GH4169has become a focus of current research.In the cutting process, the cutting temperature, strain and strain rate distribution of machined surface have important influences on the formation of the machined surface integrity (white layer, work hardening and metamorphic layer). Two-dimensional simulation of GH4169and FGH95high-speed milling process is carried out by AdvantEdge to simulate the machining of GH4169and FGH95. The distributions of temperature, strain and strain-rate in the machined surface will be investigated. Peak temperature, peak strain and peak strain rate models of the machined surface are established, which can provide the foundation for the subsequent research of surface integrity.Based on the gray level differences of metamorphic layer, white layer, dark layer and the matrix, a software system-’Image analysis software of metamorphic layer and white layer in machined surface V1.0’ is developed. The callback functions are written by the M language. This software can directly analyse the machined surface cross section images obtained from scanning electron microscopy or digital microscope. The thickness values of metamorphic layer, white layer and dark layer in the machined surface can be obtained.After the experiments of high-speed milling of PM Nickel-based superalloy FGH95and Nickel-based superalloy GH4169,’Image analysis software of metamorphic layer and white layer in machined surface V1.0’ is then used for the analysis of metamorphic layer thickness. The influence of the cutting speed on the hardening rate, the depth of hardened layer and the thickness of metamorphic layer are investigated in order to clarify the formation mechanism of the work-hardening in the machined surface of FGH95and GH4169.Through the experiments of high-speed milling of PM Nickel-based superalloy FGH95and Nickel-based superalloy GH4169, the effect of the cutting speed on white layer thickness is also investigated. Two-dimensional simulation of Nickel-based superalloys high-speed milling process is carried out by AdvantEdge. The distributions of temperature, strain and strain-rate in white layer and non-white layer region are obtained. Based on the experiments and simulation results, the phase transformation and plastic deformation mechanism of the white layer is proposed and a quantitative characterization model of the white layer formation conditions is established in order to provide theoretical guidance for the suppression of white layer of Nckel-base superalloy.This work is sponsored by National Basic Research Program of China (973)(2009CB724401).