Effect of Solute Carbon on Onset of Local Plastic Deformation in BCC Iron

Abstract

The pop-in phenomenon as a plasticity initiation during nanoindentation was analyzed to investigate the effect of solute carbon on the plastic deformation for Fe-C binary alloys and interstitial free (IF) steel. The maximum shear stress τc calculated from the critical pop-in load increases as solute carbon concentration increases. Based on a model in which the elementary step of pop-in is the nucleation of a dislocation loop, it is considered that solute carbon increases the resistance to the growth of a dislocation loop, thus higher stress is necessary for the nucleation. Frequency distributions of the pop-in load shows two peaks when the sample includes solute carbon. One peak on the lower load corresponds to the nucleation at a region of solute carbon free. The other peak on the higher load is attributed to the nucleation at a region with solute carbon. Displacement burst during pop-in Δh decreases with increase in solute carbon concentration. Considering that the Δh is proportional to the number of dislocations, it is concluded that solute carbon decreases the mean free path of dislocation movement.