Improvement in depth-sensing indentation to calculate the universal hardness on the entire loading curve

Hardness of materials depend on the applied load and on the shape of the indenter. Various models regarding the indentation size effect have been developed to evaluate this load-dependence which necessitates numerous indentation tests to be valid. The aim of this paper is to reduce substantially the number of tests by calculating the universal hardness on the entire loading curve of a load-depth registration. The use of universal hardness instead of Oliver and Pharr method is required by the comparison with the conventional Vickers hardness. The protocol can be well supported if some improvements in depth-sensing indentation are made like the consideration of the frame compliance of the instrument, the creep displacement calculated as a function of the load and the rounded tip into the indentation depth measurement and consequently into the universal hardness calculation. Additionally, we show that the indentation size effect may be well-represented by the strain gradient plasticity theory whereas significant deviation is observed when only partial depth-corrections are made. (c) 2007 Elsevier Ltd. All rights reserved.