Size effect and strain induced double twin by nanoindentation in DSS weld metal of vibration-assisted GTAW

The nanohardness values and modulus of the prior δ phase in both direct current (DC) and vibration-assisted (VIB) weld metal were higher than those of the base metal. The dislocation density in the δ phase matrix was the highest in the VIB weld metal, followed by the DC weld metal and the base metal. Therefore, the higher nanohardness value in the δ phase, especially for the VIB welding, was attributed to the existence of a higher dislocation density. By contrast, the nanohardness values of the γ phase in both weld metals were not affected by the welding process. The predicted nanohardness value of the composite phase with the rule-of-mixture was consistent with the result of nanoindentation measurements. The deformation induced a V-shaped double twin was revealed by the effect of nanoindentation on the austenite grain of the VIB weld metal.