Experimental determination and theoretical analysis of local residual stress at grain scale

Grain/phase boundaries contribute significantly to build up of residual stresses, owing to varied plastic/thermal response of different grain orientations or phases during thermomechanical treatment. Hence, accurate quantification of such local scale stress gradients in commercial components is important in understanding their mechanical performance. The current work introduces a correlative method utilizing Electron Back Scattered Diffraction and Focused Ion Beam-Digital Image slit milling methodology to accurately determine spatially resolved stress profiles in the vicinity of grain boundaries using commercially pure titanium as a model material. Measured local stress gradients were in good agreement with local misorientation values. The role of dislocation-grain boundary interactions on buildup of local stress gradients is elucidated. Stress profiles near grain boundaries initially display non Hall-Petch characteristics, followed by a typical Hall-Petch type variation of “one over square root of distance”. The observed trends allude to local stress relaxation mechanisms very close to the grain boundaries. The findings indicate that grain scale stress gradients can be significant in terms of playing a crucial role in macroscopic fatigue behavior.