Study On The Influence Of Surface Characteristics Of High Speed Cutting Titanium Alloy On Fatigue Performance

The usage rate of titanium alloy as the processing component in aviation and national defense is increasing because its light weight,high reliability and long service life.However,it is difficult for titanium alloy to obtain an ideal cutting surface because of the high hardness and brittleness.Therefore,the study of cutting surface characteristics is of great significance to improve the fatigue resistance of titanium alloy parts.This paper has taken Ti-6Al-4V and TA2 as research objects to explore the influence of surface characteristics of high-speed cutting titanium alloy on fatigue performance.The main research methods and results are as follows:1.The single factor turning test of Ti-6Al-4V was carried out to observe the surface topography after cutting and exploring the formation law of the surface topography of Ti-6Al-4V in high-speed cutting.High-cycle fatigue test was conducted on fatigue samples with different cutting surface topographies,and the sensitivity of high-cycle fatigue life to cut surface topographies was studied by combining the Peterson model.The results showed that the fatigue notch coefficient Kf increased with the deterioration of surface topographies,and the relationship between fatigue notch coefficient K_f and fatigue life was inversely proportional.The high-cycle fatigue fracture form of Ti-6Al-4V has plastic fracture.The worse the machining quality of the surface topography,the larger the dimple size of the fracture,the shallower the depth and the greater the degree of plastic fracture.2.In view of the high temperature oxidation of titanium alloy cutting surface,a comparative study was conducted on TA2 and Ti-6Al-4V,a high-speed cutting test was designed to observe the oxide layer on the cutting surface,and the formation mechanism of the oxide layer on the cutting surface of titanium alloy was analyzed by combining the first principles.The results showed that oxygen atoms oxidized on the surface of the two material systems,and oxygen atoms had stronger permeability and binding ability in Ti-6Al-4V,so the oxidation layer of Ti-6Al-4V was thicker.In the Ti-6Al-4V system,oxygen atoms first react with aluminum atoms to produce a small amount of Al₂O₃,which only exists in the outermost layer,and then reacts with titanium to generate TiO₂.TiO₂ accounts for a large proportion in the oxide layer.3.In view of the research results on the formation mechanism of oxide layer on the cutting surface,high-cycle fatigue tests were conducted on samples Ti-6Al-4V and TA2with and without oxide layer,and the difference in fatigue performance of the two materials under the two conditions was analyzed.The results showed that the sample life with oxide layer of Ti-6Al-4V and TA2 was much lower than that without oxide layer.The fatigue source of Ti-6Al-4V samples with oxide layer was generated at the oxide layer,and the instantaneous fault zone of samples with oxide layer was larger than that of samples without oxide layer.TA2 non-oxidized layer samples have slower crack initiation and propagation than those with oxidized layer.The failure mode in the instantaneous fault zone of the oxidized layer samples is brittle fracture,while the failure mode in the instantaneous fault zone of the non-oxidized layer samples is mixed ductile fracture.