Primary and anelastic creep in a high temperature near alpha-Ti alloy: Effects of microstructure and stress

The creep behaviour of a high temperature, near alpha-Ti alloy Ti6242Si has been investigated at 500 degrees C using constant stress tensile creep testing in the stress range from 150 to 350 MPa. Emphasis is put on primary and anelastic creep and their dependencies on processed microstructures, viz. globular and basket weave microstructures, and applied stress. It is shown that the primary creep strain depends strongly on microstructure. Its dependence on stress is linear in the low stress regime, whereas a weak dependence is observed for high applied stresses. Unloading experiments lead to a time dependent strain recovery which is very similar to forward creep. Unloading in the primary creep regime results in the recovery of almost all of the creep strain. However, a substantial strain recovery was also obtained upon unloading from steady state. It is shown that primary and anelastic creep strains are intimately related, and depend very similarly on microstructure and stress. The anelastic strain was found to be higher than the primary creep strain, whereas it constitutes only a fraction of the elastic strain.