The problems for radiation hardening determination of the steels under ion irradiation using instrumental indentation

The application of instrumental indentation method with the Berkovich pyramid for determination of the microhardness and radiation hardening of steels after ion irradiation is considered. The main difficulties arising in microhardness determination of a thin irradiated layer are identified. First of all, such difficulties arise when microhardness is determined with indentation diagram and the Oliver and Pharr formulae. For this case the dependence of microhardness on the indentation depth is observed even for homogeneous material. Disadvantages of microhardness determination are considered when the combine approach is used that includes processing indentation diagram with the Oliver and Pharr formulae and processing dependence of microhardness on indentation depth by the Nix and Gao diagram. A method for determining microhardness based on direct measurement of the indent projection area is proposed, which allows eliminating the influence of indentation depth on microhardness for a homogeneous material. It is shown that for a homogeneous material, the microhardness under indentation with both the Berkovich and Vickers pyramids does not depend on the indentation depth if the area of the indent projection is determined directly by measurement of its geometric characteristics. The method proposed in the work allows obtaining adequate estimates of radiation hardening of a thin layer of material irradiated by ions. The method has been verified by indentation at constant strain rate for two classes of steel: austenitic and ferritic-martensitic.