Mechanical Properties Evaluation of Bulk and Coated Material by Depth Sensing Indentation

Abstract

The mechanical characterization of materials represents an important domain of research into development. Tensile and hardness tests are generally used for such effect. Samples for tensile test require specific geometries and sizes, which often limits its use, in particular when the available amount of material is not enough to carry out the test, as in case of micro-components. The hardness test, by its simplistic and not destructive character, becomes desirable to its utilization in the evaluation of the mechanical properties of materials. The conventional hardness test consists of the application of a load on an indenter. This penetrates the sample along the direction of the normal of its surface. The load applied acts during a preset time, after which is removed, making possible the measurement of the size of the residual indentation, through optic resources. This allows the determination of the hardness, defined as the ratio between the applied load and area of the residual indentation. The optical evaluation of the area of the residual indentation is limited, namely for very low applied loads and, consequently the resulting indentations have reduced dimension. However, during the last two decades, the development of the hardness equipments not only allowed to eliminate this limitation, but also to widen the application field of the hardness test. In fact, the advent of the Depth Sensing Indentation (DSI) equipments, making possible to plot the load – indentation depth curves, extended the application of the hardness test to scales close to the atomic one. Moreover, the DSI equipments allow evaluating, not only the hardness, but also other mechanical properties, such as the Young’s modulus (Doerner & Nix, 1986; Oliver & Pharr, 1992). Other mechanical properties, such as the yield stress and work-hardening coefficient (Dao et al., 2001; Antunes et al., 2007), of bulk and coated materials can be determined from the DSI results, by applying accurate models or inverse analysis procedures. Most of the achievements reached in this domain arise from the employment of numerical tools. For example, the possibility to carry out inverse analysis, i.e. to obtain the tensile curve of bulk and coatings materials, from the experimental load – indentation depth curve obtained by DSI, was possible due to the numerical simulation of the hardness test.