Abstract
A system of nanoindentation combined with atomic force microscopy was applied to a multi-phase material for evaluating its mechanical property. A tempered martensitic steel (SCM440) with a tensile strength of 1600MPa was tested as an example of multi-phase materials, and three types of tungsten single crystals , with respective (100), (110) and (111) surface, were also tested as reference. In the tempered martensitic steel, the load-displacement behavior depends on measured positions at the specimen surface and/or sizes of deformation zone. This behavior represents inhomogeneity of the multi-phase microstructure where each component has a different mechanical property and strength. When the contact depth reaches 60nm depth, the standard deviation of nanohardness becomes a constant value. Therefore, 60nm could be the critical contact depth for disappearance of inhomogeneity effect on the deformation behavior. The constitution of the standard deviation of hardness was discussed in some detail.
