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<SUB>2</SUB>Ni grains in the inter-dendritic space. The high temperature B2 phase of NiTi is found to transform to trigonal 'R'-phase, B19'martensite, and rhombohedral Ni<SUB>4</SUB>Ti<SUB>3</SUB> 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<SUB>2</SUB>Ni 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