Fracture Toughness And Fatigue Crack Growth Rate Of TC4 Titanium Alloy In Simulated Body Fluid

TC4 titanium alloy which is one of the most widely used and promising biomedical titanium alloys has been widely used in the manufacture of head cranium,heart box,artificial joint,vascular scaffold,prosthesis,dental implant and so on,because of its light quality,memory,high specific strength,good biocompatibility and high corrosion resistance to body fluid.The materials with high fracture toughness and low fatigue crack growth rate are essential to meet the requirements of high life.When the TC4 titanium alloy used for a medical artificial bone is implanted,the fracture toughness and fatigue crack growth rate will be affected under corrosive environment.At present,there are many studies on the damage tolerance of the TC4 titanium alloy in the air,however,the influence rule and mechanism of the fracture toughness and fatigue crack growth rate of TC4 titanium alloys with different microstructures under Simulated Body Fluid(SBF)environment have not been clearly described.This article studies this issue,which provides a theoretical basis for expanding the practical application of TC4 titanium alloy in the medical field.In this paper,the equiaxed micro structure,the bimodal microstructure and the lamellar micro structure with different lamellar thicknesses of TC4 titanium alloy are obtained by adjusting the heat treatment system to obtain.The fracture toughness J of the TC4 titanium alloy in the air and SBF were measured through the SHIMADZU EHF-F1 hydraulic servo fatigue testing machine and universal testing machine.The double logarithmic curve and the Paris formula of the TC4 titanium alloy's the fatigue crack growth rate were measured through the MTS810 hydraulic servo fatigue testing machine.The fracture toughness and fracture morphology of the fatigue crack growth rate were observed by JSM-6510A scanning electron microscope and Ultra Plus field emission respectively.The crack growth path of the TC4 titanium alloy was observed by the OLYMPUS-OLS 3000 laser confocal microscope.The results show that:(1)The lamellar thickness of the lamellar microstructure obtained by multiple heat-treatment in the single-phase and two-phase region can be increased by reducing the cooling rate of the single-phase region's heat-treatment,reducing the cooling rate of the two-phase region's heat-treatment or increasing the temperature of the two-phase region's heat-treatment.When the cooling mode is the air cooling and furnace cooling after the heat-treatment of the TC4 titanium alloy's single-phase region,the microstructures are the double lamellar microstructure with short coarse secondary a lamellars in the middle of the long strip primary ? lamellars and the single lamellar microstructure without apparent secondary ? lamellars respectively.(2)In the same medium,the fracture toughness of the TC4 titanium alloy's equiaxed microstructure,bimodal microstructure and lamellar microstructure increase sequentially.When the thickness of the lamellar is between 1.90?m and 2.81?m in the lamellar microstructure,the fracture toughness of the TC4 titanium alloy increases with the increase of lamellar thickness.(3)The fracture toughness of the equiaxed microstructure,the bimodal microstructure and the lamellar microstructure in the air are higher than the fracture toughness in the SBF.Among them,SBF has little effect on the fracture toughness values of equiaxed and bimodal micro structures,and has a greater influence on lamellar microstructure.When the thickness of the lamellar is between 1.90?m and 2.810?m in the lamellar microstructure,the greater the influence of SBF on fracture toughness with the increase of lamellar thickness.(4)The crack growth rate of the TC4 titanium alloy's equiaxed microstructure,bimodal microstructure and lamellar microstructure decrease sequentially in the air.In the SBF,when the ?K is less than 6.2 MPa·m^0.5,the fatigue crack growth rate of the equiaxed microstructure,the bimodal microstructure and lamellar microstructure reduce sequentially;when the ?K is between 6.2 MPa·m^0.5 and 15 MPa·m^0.5 in the partial threshold region and the Paris region,the equiaxed microstructure and the lamellar microstructure's fatigue crack growth rate that are higher than the crack growth rate of the duplex microstructure are approximately equal;when the ?K is more than 15 MPa·m^0.5,the crack growth rate curves of the three kinds of microstructures are coincident basically.(5)The fatigue crack growth rate of the TC4 titanium alloy's the equiaxed microstructure,bimodal microstructure and lamellar microstructure in the SBF(36.5±0.2)? are higher than that in the air;SBF has a great influence on the fatigue crack growth rate of the lamellar microstructure,and has little effect on equiaxed and bimodal microstructures.