STUDY OF YIELD STRESS AND DUCTILITY OF REINFORCED SURFACE LAYERS OF METAL ALLOYS BY INDENTATION

Abstract

Indentation was employed to study the mechanical properties of the surface layers of metal alloys, hardened by severe plastic deformation methods using AISI O2 and AISI 316L steels and D16 aluminum alloy. Most scientific papers evaluate the mechanical properties of hardened surface layers and thin coatings by determining only their hardness. However, hardness alone cannot characterize the ductility of a material without modern concepts used to determine the physical ductility from hardness. The mechanical behavior of a material can only be characterized by determining both the ductility and the yield stress. These both quantities can be found by micro- or nanoindentation. We developed indentation methods to determine the physical plasticity d_Н and yield stress s_SH of surface layers of metal alloys hardened by various techniques (with analysis of changes in these characteristics along the depth of the hardened layer) to select the optimal hardening method. The hardening characterized by the ratio between the yield stresses of the hardened layer and starting material (s_SHhard/s_SHstart) was much greater for all studied alloy than the hardening characterized by the hardness ratio (HV_hard/HV_start). Thus, the use of the d_H and s_SH values obtained from standard microhardness measurements increases the information content and efficiency of the indentation method in studying the mechanical behavior of metal alloy layers hardened by various methods.