Impression creep behaviour of different zones of pulsed gas tungsten arc welded Ti-6Al-4V alloy

Abstract

Ti-6Al-4V alloy has several industrial applications, because of their excellent combination of mechanical and physical properties. However, welding of Ti-6Al-4V alloy is very challenging due to its high reactivity with atmospheric gases at elevated temperatures (as low as 480 °C). In this work, defect-free bead on plate welding has been carried out on 3 mm-thick Ti-6Al-4V sheets with the help of an indigenously developed shielding set-up, using the pulsed gas tungsten arc welding (GTAW) process, and the impression creep responses of different zones of the weld have been investigated using the impression creep method. A detailed microstructural examination has been carried out, because the creep behaviour of each zone is dependent on the microstructure of that region. Base metal revealed a typical fine bi-modal microstructure with an average grain size of 4.2 µm, but there was significant grain coarsening in the heat affected zone (HAZ) and weld zone with an average prior β grain size of 37 µm and 105 µm respectively. Weld zone and HAZ also showed Widmanstätten morphology as fine laths of α inside the prior-β grains. Coarse prior-β grains and Widmanstätten morphology in HAZ and weld zone assisted in reducing grain boundary sliding and impeding dislocation glide, respectively, which led to an improvement in the creep resistance of these zones in comparison to base metal. In the testing range, dislocation creep appeared as the governing creep mechanism, where activation energies ranged from 255 to 312 kJ-mol−1 in different zones of the weldment.