Creep of Ti-5Al-5Mo-5V-1Fe-1Cr alloy with equiaxed and lamellar microstructures

The influence of microstructure on creep behavior of Ti-5Al-5Mo-5V-1Fe-1Cr (TC18) alloy at 350-500 °C and tensile stress of 200-400 MPa was investigated by creep testing and transmission electron microscope (TEM). The creep mechanism was discussed by microstructure evolution. The results showed that, the alloy with lamellar structure showed better creep resistance than that of equiaxed structure. At 350-400 °C, the stress exponent n of samples with both structure was in the range of 1.2-1.9, the creep was controlled by a/3〈112¯0〉 dislocations gliding on {101¯0} prism plane, {0002} basal plane and {101¯1} pyramidal plane. The creep activation energy of samples with both structure increased from 119 to 364 kJ/mol, with the increase of tensile stress from 200 to 400 MPa. At 450 °C, the stress exponent n of samples with both structure was about 3.0. At 500 °C, n is 4.3-4.8 under lower tensile stress, and 8.2-8.5 under higher tensile stress. At 450 °C and 500 °C, there was a dramatical rise of total creep strain, the jogged dislocation glided on {0002} basal plane was dominated, and the creep was controlled by dislocation climb.