Use of Modeling Based, Physical Simulation to Reveal the Relationship Between Process Parameters and Microstructural Evolution in Thermal Stir Processed (TSP) TI6A1-4V

摘要

The initial work statement targeted quantifying the hot working conditions experienced by titanium during friction stir welding/processing (FSW/P). Of particular interest was the identification of the hot working conditions (i.e. strain rate, strain, and temperature) required to refine the grains in the weld zone or nugget. Using a kinematic approach toward modeling of the FSW/P, the instantaneous shear strain rate encountered by the material entering the rotation plug around the weld tool is estimated to be in the range of 103 to 106 s-l at strains levels in excess of 50. A similar level of grain refinement has been reported in metal chips formed during cutting operations where the shear strain rate is estimated to be in the range of 103 to 106 s-l, but at strain levels less than 5. Both these processes are predicted to instantaneously impart strain rates on the order of ballistic impact on the metal. In contrast grain refinement has also been reported in equal channel angular extrusion (ECAE) where the grain size reduction has been correlated with the increasing amount of strain achieved by multi passes at quasi-static strain rates. The motivation for this study is furthering our understanding of the mechanics responsible for grain refinement as influenced by ballistic level sheer strain rate and/or shear strain.