Materials characterisation part II: tip geometry of the Vickers indenter for microindentation tests

This is the second of two papers by the authors associated with materials characterisation methods based on hardness testing. It is important to have knowledge of the tip geometry of the indenter employed in the hardness test as this affects the correctness of the value of contact area parameter used to determine the mechanical properties. In this paper, outcomes of a study concerned with the tip geometry of the Vickers microindenter are presented. Results from experiment are compared with results from published works and the most current accepted analytical models. A new non-contact methodology based on a residual imprint imaging process is developed and further compared with other methods using experimental and numerical analyses over a wide range of material properties. For confirmation, an assessment was undertaken using numerical dimensional analysis which permitted a large range of materials to be explored. It is shown that the proposed method is more accurate compared with other methods regardless of the mechanical properties of the material. The outcomes demonstrate that measuring contact area with the new method enhanced the overall relative error in the resulting mechanical properties including hardness and Young’s modulus of elasticity. It is also shown that the value of the contact area using actual indenter geometry obtained from experimental load-displacement analysis or FEM numerical analysis is more accurate than the value obtained from the assumption of perfect indenter geometry and hence can be used for materials with low strain hardening property. © 2017 Springer-Verlag Londo

Hardness of FRHC-Cu determined by statistical analysis

A statistical indentation method has been employed to study the hardness value of fire-refined high conductivity copper, using nanoindentation technique. The Joslin and Oliver approach was used with the aim to separate the hardness (H) influence of copper matrix, from that of inclusions and grain boundaries. This approach relies on a large array of imprints (around 400 indentations), performed at 150 nm of indentation depth. A statistical study using a cumulative distribution function fit and Gaussian simulated distributions, exhibits that H for each phase can be extracted when the indentation depth is much lower than the size of the secondary phases. It is found that the thermal treatment produces a hardness increase, due to the partly re-dissolution of the inclusions (mainly Pb and Sn) in the matrix

Application of the work of indentation approach for the characterization of aluminium 2024-T351 and Al cladding by nanoindentation

Nanoindentation has been used to characterize the mechanical properties of aerospace-grade Al2024-T351 with and without a clad layer of pure aluminium. The clad layer is introduced by means of a roll-bonding process which can cause significant work-hardening of the material in the clad layer. The hardness and Young’s modulus of the pure aluminium and the Al2024 have been determined by a number of methods, including the traditional Oliver and Pharr method, and a number of other methods, including direct measurement of the indentation by atomic force microscopy, and evaluation of the work of indentation. The Oliver and Pharr method was found to underestimate the area of contact as it did not include the area of piled-up material around the indentation periphery. This gave a corresponding overestimation of both hardness and modulus. The area of the indentation measured by atomic force microscopy was similarly found to underestimate the contact area owing to relaxation of material around the indent between indentation and imaging. The work of indentation approach was found to give good agreement between the hardness calculated by nanoindentation and those found in the literature