Issues Concerning Small Additions of Ni to Ti Friction Stir Welds

Recent experimental measurements, involving small additions of Ni foil to CP-Ti friction stir welds (FSWs), have motivated a re-evaluation of issues concerning material flow and the resulting microstructure in these welds.  One issue concerns the fact that the Ni additions improved weld microstructure.  This implies the need for a better understanding of the basic mechanisms whereby the introduction of small amounts of this fast diffuser into the stirred region results in improved microstructure and associated improvements in weld performance.  Another issue concerns the fact that a relatively high level of detailed information related to material flow patterns occurring in FS welds of Ti can be experimentally measured by x-ray microtomography using the introduced Ni as a flow tracer.  This potential availability of large amounts of flow pattern information for Ti FSWs, informs our need for a predictive methodology that incorporates large amounts of flow pattern information.