Phase formation in Ti/Ni dissimilar welds

We explore phase formation in Ti/Ni dissimilar welds using a combination of microscopy and composition analysis (TEM, SEM and EDS).Main microstructural features are NiTi dendrites and $Ti_2Ni$ grains in the inter-dendritic space. The high temperature B2 phase of NiTi is found to transform to trigonal 'R'-phase, $B19^{\prime}$ martensite, and rhombohedral $Ni_4Ti_3$ phase; these different transformation products highlight the composition inhomogeneity in the parent B2 phase and probable non-equilibrium solidification events during rapid cooling of the weld. Solidification sequence of NiTi and $Ti_2Ni$ was found to vary depending on local conditions in the weld. Formation of impurity nitride phases of titanium is observed which signify incomplete shielding during welding