Microhardness tests for high energy neutron source experiments

Abstract

In a development effort to extract mechanical property information from miniature specimens, standard diamond pyramid microhardness (DPH) tests have been conducted at Hanford Engineering Development Laboratory (HEDL) on specimens irradiated in the rotating target neutron target neutron source (RTNS-II); and techniques to extend the information available from microhardness tests have been developed at the University of California, Santa Barbara (UCSB). In tests at HEDL, radiation hardening has only been observed in pure metals irradiated to neutron fluences less than 4 × 10 21 n/m 2. In copper, specifically, a proprotional increase in the DPH with neutron fluence has been observed, and this microhardness increase has been correlated with an increase in the 0.2 percent offset yield strength. At UCSB it has been found that hardness and microhardness data obtained with spherical indenters can be used to determine the true stress-true plastic strain relationship of the test material; moreover, it has been found that features of the indentation lip geometry can be used to characterize localized flow phenomena like Lüders strain in steel. Consequently, microhardness test techniques appear attractive for small specimen test applications.