Study Of Tensile Creep Behavior Of A Powder Metallurgy Ti-45Al-7Nb-0.3W-0.1B Alloy

TiAl intermetallic is promising lightweight and high strength structural materials for elevated-temperature applications in advanced industrial fields such as automobile industry,aerospace industry and weapon manufacturing.In these applications,the creep resistance of alloys is an important criterion to evaluate their application value.In this paper,Ti-45Al-7Nb-0.3W-0.1B alloy was developed by powder metallurgy method.The creep resistence and creep deformation mechanism of the alloy after heat treatment were investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),tensile test and tensile creep test at high temperature.The results are as follows:(1)The microstructure evolution of the alloy during heat treatment was explored.With the increase of heat treatment temperature and time,the size of lamellar colonies increases.With the increase of heat treatment temperature,the content of residual γ grains between lamellar colonies decreases.The ultimate tensile strength of alloy after 30 min annealing at1380℃ reaches 450 MPa and 435 MPa at 750℃ and 800℃.(2)The accuracy of Theta constitutive equation describing and predicting creep behavior is studied.The creep curves under all creep conditions were fitted by the Theta constitutive equation,and the creep curves under all creep conditions were calculated and predicted based on the fitting creep curves of 750℃,260 MPa,270MPa and 300 MPa and those of 800℃,220 MPa,240MPa and 280 MPa.The comparison between the predicted and experimental results of creep curves at 800℃,200 MPa show that the Theta constitutive equation has a good predictive effect on creep behavior.(3)The effects of creep temperature and creep stress on the creep behavior of alloy are clarified.In the experimental range of temperature and stress,temperature affects the deformation ability of lamellar colonies,and stress affects the deformation incompatibility between lamellar colonies.With the increase of creep stress,the creep strain at750℃ is at the same level,about 10%,and the creep strain at 800℃increases gradually,from 12% at 200 MPa to 20% at 280 MPa.