Plasticity initiation behavior that appears as a pop-in phenomenon on a loading process during indentation-induced deformation was investigated to reveal the effects of lattice defects such as grain boundary and solute element for various metallic materials including Fe alloys through instrumented nanoindentation techniques. The critical load P c of pop-in on a loading process is lower in the vicinity of the grain boundary than in the grain interior, but the relative hardness of the boundary is equal to or greater than that in grain interior. In-solution Si produces a larger increase in the P c for both the grain boundary and the grain interior in the Fe-Si alloy than in the interstitial-free steel. The maximum shear stress corresponding to the P c underneath the indenter is directly proportional to the shear modulus in single crystals with various crystallographic structures. Microstructural effects on the P c are considered based on some dislocation models.
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