A study on strengthening and toughening mechanism of laser beam welded joint prepared between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb

Abstract

In this study, laser beam welding (LBW) between Ti–22Al–27Nb and Ti–6Al–4V was experimented with and without an interlayer of Nb to analyze and compare the effect of Nb on evolution of microstructure in fusion zone (FZ) and its impact on weld joint performance at room as well as high temperature (650 °C). The nucleation and evolution of phases and crystals were examined through X-ray diffraction (XRD), electron probe microanalysis (EPMA), electron back scattered diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and high angle annular dark field (HAADF) imaging, respectively. The weld joint performance was evaluated through tensile and hardness tests. The adulteration of LBW joint between Ti–22Al–27Nb and Ti–6Al–4V through pure Nb contributed an increase of 28.70% in yield strength (YS), 10.22% in ultimate tensile strength (UTS) and 12.81% in percentage elongation. The evident reason for such an improvement in joint performance was attributed to the suppression of α′ martensite and nucleation of single phase B2 with fine grained structure, which provided greater fraction of high angle grain boundaries (HAGBs) in FZ. The LBW joint between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb was ruptured from the base material (BM) Ti–22Al–27Nb during tensile straining at room temperature. All the LBW joints between Ti–22Al–27Nb and Ti–6Al–4V, either prepared with or without an interlayer of Nb, were fractured from the BM Ti–6Al–4V during tensile test at 650 °C.