Anelastic phenomena at room temperature in Ti6Al4V produced by electron beam powder bed fusion

Anelastic phenomena was studied at room temperature in Ti6Al4V produced by electron beam powder bed fusion (E-PBF). Samples were studied in the as-built and post-treated state and were compared with extruded and annealed material. Cyclic loading under tension-compression performed in the elastic regime (total strain of +/- 0.75%) revealed that the loop area increases with the number of cycles up to 100 cycles in all cases studied. The largest loop area was found for the as-built sample where residual stresses are still present. Smaller loop area form by specimens that underwent heating above 700 C which also exhibit low tension-compression anisotropy. Stress relaxation experiments at constant total strain, epsilon(0), in the elastic regime (+/- 0.35%, +/- 0.60% and +/- 0.75%) and at 1% and 4% showed that the relaxation time calculated using the standard linear solid (SLS) model decreases almost linearly with the increase of the initial stress normalized by the proportional limit. For strain of +/- 0.60% the relaxation time was below 70 min in tension and below 35 min in compression. From all the measurements we generally assume that the anelastic phenomena in Ti6Al4V at room temperature is related to bowing-out of dislocations, with a possible contribution of formation and motion of twin walls.