Effect Of Milling Parameters On Surface Integrity And Low Cycle Fatigue Performance Of GH4169 Superalloy

Nickel-based superalloy GH4169 is a kind of difficult-to-machine material widely used in the aerospace field.Because of its service in high-temperature and high-stress working environments,low cycle fatigue failure often occurs.Different processing methods and processing parameters will affect the fatigue life.Therefore,this paper focuses on the effects of different processing parameters on the low-cycle fatigue performance of the machined parts.Based on the surface integrity index under different milling parameters,the effect of different processing parameters on the surface integrity index was explored and the reason for the difference low cycle fatigue life was revealed by the difference surface integrity.And empirical formulas for different machining parameters and surface integrity indexes,as well as math formulas for different machining parameters and low cycle fatigue life are provided.So the low cycle fatigue life would have a basis calculation.First,the samples to be tested are processed under different milling parameters,including milling,wire cutting and grinding processes.The experimental sample grain size was about 100?m.For the research of the machining surface integrity,an experimental test analysis method was adopted.The main surface integrity index studied are surface roughness in external effects and micro-hardness and residual stress in internal effects.Comprehensively analyze the influence of different milling parameters on the surface integrity of GH4169 from the internal and external effects of the cutting surface to optimize the processing parameters.Finally,the low-cycle fatigue life under different milling parameters was tested,and the characteristics of fatigue fractures were analyzed including the fatigue crack origin region,crack propagation region and transient fracture region.The relationship between low-cycle fatigue strength on surface microhardness,surface residual tensile stress,and stress concentration factor was established.The results show that the degree of influence on the low-cycle fatigue life is:cutting depth>cutting speed>feed speed.Through the setting of milling parameters,the length of low-cycle fatigue life can be roughly estimated.The cutting speed and cutting depth can effectively change the low-cycle fatigue life of the machined part.On the premise of guaranteeing the processing efficiency,a smaller cutting speed and a larger cutting depth can be used for processing.The mechanism of low-cycle fatigue fracture of the superalloy obtained from the low-cycle fatigue fracture is that the sample undergoes internal plastic deformation under the load cycle above the yield strength,which causes the initiation and expansion of the fatigue crack source,and finally causes the sample to fracture.The fracture mode is a tough-brittle mixed fracture mode.