Investigation On Formation Mechanism Of Deteriorative Layer On Machined Surface Of GH4169 Superalloy Under High-Pressure Cooling

Aerospace parts material GH4169 is a kind of typical difficult-to-machine material,which has low thermal conductivity and poor cutting performance.It is affected by plastic deformation and uneven distribution of the structure during conventional processing,and the surface is prone to process metamorphic layer.The metamorphic layer is used as an evaluation index of surface quality,and its microstructure form,content and distribution will affect the mechanical properties of the processed surface and the formation of microscopic cracks.With the development of cutting assisted machining technology,the application of high-pressure cooling assisted machining technology can effectively improve the quality of the processed surface.However,the micro-evolution mechanism of the metamorphic layer under high-pressure cooling conditions is still lacking.In this paper,nickel-based high temperature alloy GH4169 is used as the research object,and high-pressure cooling assisted machining technology is combined with theory and simulation to predict and analyze the micromorphology,composition structure,and influencing factors of the surface metamorphic layer.The formation mechanism is studied.Firstly,by analyzing the thermal characteristics of the high temperature cutting process,Deform-3D is used to construct a thermo-mechanical coupled finite element model of GH4169 turning under high pressure cooling,and the temperature and deformation fields of the processed surface during hard cutting are simulated and analyzed.The peak prediction model of the processed surface temperature field is established through regression analysis,which provides a theoretical basis for the subsequent research on the formation mechanism of the processed surface metamorphic layer.Secondly,based on the thermodynamics of alloy phase transition and metal plastic deformation dislocation theory,a model for predicting the energy dissipation and thickness of micro-plastic deformation layers under high-pressure cooling is established;based on the PCBN tool cutting GH4169 test under high-pressure cooling,the application Scanning electron microscope(SEM),X-ray diffraction analysis(XRD),microhardness tests and other micro-observation methods,explore the microstructure and mechanical properties of the processed surface metamorphic layer,and analyze the phase and reprocessing of the processed surface metamorphic layer The degree of crystallization;by changing the cutting conditions,exploring the influence of cutting parameters such as cutting speed and feeding rate and cooling pressure on the metamorphic layer,establishing a prediction model of the metamorphic layer under high-pressure cooling conditions,and then providing techniques for studying the formation and control of the metamorphic layer stand by.Finally,based on the characteristics of high strain rate and short time-effect during cutting,the micro-evolution law of the recrystallization behavior of the modified surface of GH4169 processed surface under high pressure cooling was explored to reveal the formation mechanism of grain refinement in the modified layer and further explore the modification layer of microscopic crack propagation.Research on the micro-evolution law and formation mechanism of the processed surface metamorphic layer under high-pressure cooling provides a certain theoretical reference for optimizing the surface quality of difficult-to-machine materials and improving the service performance and service life of high-temperature alloy parts.