NANO AND MACRO INDENTATION STUDIES OF POLYCRYSTALLINE COPPER USING SPHERICAL INDENTERS

摘要

Indentation studies of polycrystalline heavily work-hardened and annealed oxygen-free copper have been made using spherical indenters of radii 7, 35, 60, 200 and 500 μm. In the case of the 200 and 500 μm radii indenters an Instron mechanical testing machine was used for applying the load, whereas for the smaller indenters a UMIS 2000 machine was used. It is shown that the relationship between the mean indentation pressure, P_m and α/R (i.e. indentation stress-strain), where a and R are the radii of the circle of contact and indenter, respectively, is independent of indenter radius, provided the indentation radius, α, is correctly measured. It is also shown that in the case of the work-hardened copper, the departure from the elastic behaviour occurs at P_m ≈ 1.1 Y, where Y is the uni-axial yield stress of the copper. In the case of the annealed copper, although the P_m vs α/R curve for the smallest indenter has the same form as for the 200 and 500 μm radii indenters, the values of P_m are higher by 50% over the enitre range of α/R. It is discussed that the spherical indentation hardness measurements, using micron-sized spherical indenters, provide a suitable method for estimating the yield stress of thin coatings and surfaces.