Understanding the effects of ion irradiation using nanoindentation techniques

Abstract

The effects of ion irradiation in materials for research are usually limited to a shallow surface layer of the order of one micrometre in depth. Determining the mechanical properties of such irradiated materials requires techniques with high spatial resolution. Nanoindentation is a relatively simple method for investigating these shallow layers with the advantage that statistically rich data sets for elastic and plastic property values can be generated. However, interpretation of the results requires and understanding of the material response, including the extent of the plastic zone with respect to the irradiated layer, pile-up or sink-in of material around the indentation site that affect the calculated contact area and hence derived mechanical property values. An Fe + self-irradiated Fe12%Cr alloy was investigated with three different indenter tip geometries, a Cube corner, Berkovich and 10 micron radius indenter. Sharp indenters provide sufficiently small plastic zones to be contained within the irradiated layer but pop-in events and pile-up need to be taken into account for correct interpretation of the mechanical properties of the irradiated material.

Evaluation of Ion-Irradiation Hardening of Tungsten Single Crystals by Nanoindentation Technique Considering Material Pile-Up Effect

“…(3) of the elastic modulus of the indenter E I and the actual elastic modulus of the material E S , using E I = 1141 GPa, υ I = 0.07 11) for a diamond tip and E S = 410 GPa 11) , υ S = 0.28 for W. Therefore it can be said that E S is associated with the true projected area of contact including pile-up A P EMC . Note that the symbols used in this study as shown in the List of Symbols are somewhat different from those in the original works by S. I. Bulychev [28][29][30][31][32] , or as in Heintze et al 21) , Beck et al 22) and Hardie et al 23) Heintze et al s 21) pileup corrected hardness method, which can be called as the elastic modulus correction (EMC) method, was assessed on unirradiated, neutron irradiated and self-ion-irradiated 9 mass% Cr f/m steel T91. An advantage of the EMC 21) method is that one actually does not have to measure the pileup height, but can use the latter expression of H EMC in eq.…”

“…Based on the ndings by Sneddon 27) as well as later on by other researchers, Bulychev, Alekhin, Shorokov and their co-workers [28][29][30][31][32] , Heintze et al 21) , Beck et al 22) and Hardie et al 23) recently proposed different methods for pile-up corrected hardness. In eq.…”

“…Further on, based on their 22) transient grating laser measurement results, they assumed that the elastic modulus of the specimen was changed after ion-irradiation. Hardie et al 23) on the other hand recently used the concept of area expression of eq. (5) to calculate a pile-up corrected hardness for iron ion-irradiated (6.18 dpa at 593 K) Fe-12mass%Cr alloy, H/A actual /A cc , which required thorough measurement of the area by scanning electron microscopy (SEM), which is called as the pile-up correction (PUC) method 23) .…”

“…Since describing the full shape of this area, A P EMC , is dif cult, as can be seen in Hardie et al 23) , we focused on a so called representative depth including pile-up, z calc.…”

“…Also, these EMC methods require no thorough measurement of contact areas of remained indenter imprints, although Hardie et al 23) suggested the possible way to measure the actual area of contact by scanning electron microscopy (SEM).…”