The Issues of the Radiation Hardening Determination of Steels After Ion Irradiation Using Instrumented Indentation

The application of the instrumented indentation method with a Berkovich indenter (triangular pyramid) is considered for the determination of microhardness and radiation hardening of ion-irradiated steels. The main difficulties arising in the assessment of the microhardness of a thin irradiated layer are identified. They are connected with the indentation depth effect on microhardness even for homogeneous materials when the indentation diagram is used. A method of microhardness determination is proposed that is based on direct measurement of the indent projection area, taking into account the formed pile-ups. The proposed method allows one practically to exclude the influence of the indentation depth on the microhardness of homogeneous material at least over the depth range from 0.2 to 4 μm and to obtain an adequate assessment of the radiation hardening for a thin irradiated layer with a depth of about 2 μm. Moreover, a formula is proposed for taking into account the influence of pile-ups on the microhardness determined from the indentation diagram using the Oliver–Pharr method. The proposed method and the formula are verified for austenitic and ferritic-martensitic steels.