Study On Microstructure And Properties Of The TC18 Titanium Alloy

With the development of aerospace industry,the demand for new titanium alloys with high strength and high fracture toughness is becoming more and more urgent.As a near-?titanium alloy TC18 alloy,can be used in the manufacture of 350⁴00?lasting work of the wing force parts,fuselage and operating systems and other fasteners,but also for the manufacture of less than 350?working engine of the leaves and fan plates.Therefore,it is very important to explore the relationship between the processing parameters and the microstructure and properties of TC18 alloy.In this paper,the fracture toughness K_IC,the crack growth rate da/dn,the room temperature fatigue performance S-N and the fracture behavior of TC18 alloy with lamellar structure were studied and compared with the properties of BT22 inlet forgings with equiaxed tissue.The main research results are as follows:The fracture toughness test results show that the K_IC value distribution of the longitudinal specimen is uniform and the average value is 77.2MPa·m^0.5.The fracture toughness K_IC value of the transverse specimen is dispersed and the difference between the maximum value and the minimum value Is 27.1 MPa·m^0.5,the average value is69.4MPa·m^0.5 Compared with BT22 imported forgings,the fracture toughness K_IC value of TC18 alloy domestic forgings is higher because the lamellar resistance of TC18alloy forgings is better than that of BT22 inlet forgings with equiaxed tissue.The crack propagation rate test results show that the crack propagation rate of the TC18 alloy domestic forging increases with the increase of the stress ratio R,and the effect of the stress intensity factor?K on the crack propagation rate decreases.Under the same stress ratio,the TC18 alloy is made Forging L-T has a lower crack growth rate da/dn compared to T-L.Compared with BT22 inlet forgings,the crack propagation rate da/dn of TC18 alloy domestic forgings is relatively low when the stress ratio R is the same.The results show that with the increase of the stress ratio R,the fatigue strength of the forged forgings of TC18 alloy increases.The stress distribution ratio of TC18 alloy is mainly due to the microstructure,Which belongs to the dimple fracture.At the stress ratio R=-1,the morphological characteristics of the cleavage fracture are mainly manifested in the fracture surface morphology,which belongs to the brittle fracture.In the same fatigue life,BT22 imported forgings fatigue strength is better than TC18 alloy.However,through comprehensive analysis,it can be seen that the strength and toughness matching of TC18 alloy forgings is better than that of BT22 inlet forgings to meet the comprehensive performance requirements of materials for bearing structure of an aircraft.