The Effects Of Fe On The Mechanical Behaviour Of TA15 Titanium Alloy

TA15 titanium alloy(with a nominal composition of Ti-6Al-2Zr-1Mo-1 V)is a kind of near-a alloy with high aluminum equivalents,and possesses both the advantages of a and(?+?)titanium alloys.Therefore,the alloy has been widely used in the manufacture of engine parts and airframe bearing components,In order to meet the higher requirements of aeronautical structures,fine adjustment of alloy composition has usually been adopted because of its economical and efficient aspects except for optimizing thermal deformation processes.Fe has been widely used as strengthening element in high-strength titanium alloys.In this paper,a comparative study on the mechanical properties of TAl5-Fe(artificially added 0.2wt.%Fe element)and TA15(no artificially added element Fe)titanium alloys was done and could provide evidence for further optimizing the mechanical properties of the alloy.The effects of Fe on the microstructure and tensile properties of the alloy were studied.The results showed that,0.2wt.%Fe had no obvious effect on the morphology of the alloy.Tensile strengthes of TAl5-Fe alloy were 10?15 MPa higher than those of TAl5 alloy due to the solid solution strengthening effect,while elongation and reduction of area of the two alloys exhibiting indentical.More work need to be done to reveal the mechenism of no plastic decline.Besides,0.2wt.%Fe had no obvious effect on the the impact energies and impact toughnesses of the two alloys.The influences of Fe on the endurance and creep properties of TA15 alloy were investigated.The results showed that,the rupture life of TAl5-Fe alloy at 500? was lower than TAl5 alloy due to the faster diffusion rate and the accelerated plastic deformation.The effect of Fe on the creep resistance of the two alloys was temperature-related:within the range of 250?500?,Fe reduced creep resistance,while from room temperature to 250?,Fe had opposite effect on creep resistance.It was found that,Fe significantly improved the diffusion rates of atoms and accelerated the dislocation motion at high-temperatures,thereby inceasing creep deformation.Whereas diffusion was weak below temperatures of 250?.As solution strengthening element,Fe could block the movement of dislocations,thereby decreasing creep deformation rate.Further analysis showed that within the range of 200?400 ?,creep stress exponents of the two alloys exhibited from 4.0 to 6.4,implying that the creep mechanism confirmed to the mechanism of dislocation climbing.However,the calculated creep activation energies of the two alloys were lower than the self-diffusion activation energy of Ti atoms,which indicated that the creep mechanism within the temperature of 200?400 ? range was not indentically compared with the well known mechanism of dislocation climbing.In addition,the effects of Fe on the creep properties of Ti-6Al-4V titanium alloy were also studied,and the conclusions were consistent with those in the two TAl5 titanium alloys.The effects of Fe on the fracture toughness and fatigue crack propagating properties of the two alloys were compared.The results showed that the 0.2wt.%Fe had no obvious influences on fracture toughness at both room and higher temperatures.Furthermore,the fatigue crack growth rates of the two alloys at room temperature and 200? were basically indentical.However under the condition of 500?,the crack growth rate of TA15-Fe alloy was faster than that of TA15 alloy,especially in the case of the 0.5 load ratio.That should be explained by the process of Fe speeding up diffusion rate at high temperature and reducing the resistance of crack propagation.