An application of the ultra-microhardness technique to high-energy ion-irradiated copper for evaluating stress-strain properties

We proposed a method for evaluating stress-strain properties of fcc metals solely by ultra-microhardness (UMH) technique in the previous paper. This paper deals with its application to pure copper irradiated with 100 MeV I⁷⁺ ions. UMH measurements at 0.1 g and TEM observations are carried out on specimens prepared in cross section, and the value of the strain-hardening exponent (n) and the 0.2% yield stress (σ_0.2) are evaluated as a function of the penetration depth of ions. The value of σ_0.2 is compared with that obtained by the conventional method without taking work-hardening into consideration. The conventional method overestimates σ_0.2 at the depth where the value of n is evaluated not to be zero, demonstrating the importance of our method for evaluating σ_0.2 of metals whose values for n vary with irradiation. The increment of σ_0.2 obtained by our method is analyzed in terms of the density of defect clusters, and it closely follows the expected relation for irradiation-induced hardening caused by defect clusters.