Corrosion Fatigue Properties Of TC4 Titanium Alloy

TC4-DT titanium alloy is a medium strength and highly-damaged tolerance type titanium alloy,which is widely used in the key bearing parts of aircraft.Aircraft in actual work often suffer damage from the corrosive environment,such as brine and heavy metal oil solution.Therefore,studying the corrosion fatigue of TC4-DT in 3.5%NaCl solution and tank water solution can solve practical engineering problems.This paper mainly studies the corrosion fatigue properties of TC4-DT titanium alloy.The order of fatigue life affected by environment is as follows:water tank,3.5%NaCl solution and Room temperature air.The corrosion damage and fatigue damage are in competition.Under high stress level,the fatigue life of the specimen is mainly affected by the alternating load;Under low stress level,the fatigue life of TC4-DT is mainly affected by the corrosion environment;When K_t=1,the tank water has the greatest effect on the fatigue life of the test piece,followed by 3.5%NaCl solution and laboratory air environment,and the smaller the cyclic load applied,the greater the effect;When K_t=3,the fatigue life of 3.5%NaCl solution and water tank environment due to the notch effect is similar to those in the laboratory air environment.Through the low-cycle stress corrosion test,the results show that the titanium alloy has a large notch sensitivity.The corrosion environment has similar influence on the fatigue properties of TC4-DT titanium alloy notched specimens and does not account for the main factors.The TC4-DT notch specimens Crack initiation is mainly caused by local stress concentration.Through the low-strain strain control corrosion fatigue test,it is found that the TC4-DT titanium alloy has obvious characteristics of cyclic softening.The cyclic deformation behavior of the TC4-DT notched specimen mainly depends on the strain amplitude and the change of the corrosion environment has less effect on it.SEM observation of the fatigue fracture shows that under the corrosive environment,the crack of the titanium alloy mainly occurs on the surface of the specimen,and the fatigue fracture has obvious multiple fatigue sources under the corrosion environment.Under high-cycle fatigue,bands are observed in the crack propagation zone,accompanied by secondary crack.Low-cycle fatigue crack propagation zone is shorter,there is no large area of fatigue band.There are a large number of dimples in high and low cycle corrosion fatigue instantaneous area,which is obvious cleavage fracture characteristics.